Omega Owners Forum
Chat Area => General Discussion Area => Topic started by: Pitchfork on 24 February 2008, 16:14:13
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I never recall having seen a failure of an engine in a Motor cycle or Car, failing because of a push-rod problem or failure!
So - why do we now have over-head camshafts, & perhaps
more critically, camshafts driven by rubber-bands?
Seems to me that if you do have to have OHC, that chain driven are more reliable/ economical to maintain (e.g. Traktors, Nissan Micras) than these wretched belt-driven lumps (unless of course they provide a good excuse for a Beery weekend get-together for readers of the ultra-right Daily Mail!)
Discuss :-?
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Interesting points... but not having oil immersed timing chains has contributed towards car manufacturers being able to increase servicing schedules ::)
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Interesting points... but not having oil immersed timing chains has contributed towards car manufacturers being able to increase servicing schedules ::)
....and inserting expensive, time-consumming & profitable cam-belt changes into the shedules!!
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Yep probably very true.
Chains are known to stretch over time and the guides tend to break up around 100K.
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Chains can go too (or more to the point guides/tensioners). A mate's V8 Diesel self destructed at 88K miles 10 days ago when the chain slipped. :o
Chains are often at the back of the engine, so it's an engine out job to replace them. Not that belts are a great solution. At least it's pretty easy to change on the miggy.
As James said, pushrod engines have chains too. Those guys will convert the chain to gears for near absolute robustness.
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Interesting points... but not having oil immersed timing chains has contributed towards car manufacturers being able to increase servicing schedules ::)
....and inserting expensive, time-consumming & profitable cam-belt changes into the shedules!!
;D ;D
Tbh, I think it's swings and roundabouts.. there are pro's and cons of each. but I think going back to the original Q, the reason for implemenging OHC engines is because they are mroe capable of delivering the power and efficiency that the market requires..
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Yep probably very true.
Chains are known to stretch over time and the guides tend to break up around 100K.
Poll? How many Traktor owners on the forum have had to replace a timing chain?
I'm at 140K currently
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As James said,
James hasn't posted on this thread - he is outside cleaning out the car ::) ::) ;D
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Yep probably very true.
Chains are known to stretch over time and the guides tend to break up around 100K.
Poll? How many Traktor owners on the forum have had to replace a timing chain?
I'm at 140K currently
I was really referring to the Senator / Carlton 24V straight six petrol lump, afraid I know little / nothing about the BMW straight six deisel.
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Interesting points... but not having oil immersed timing chains has contributed towards car manufacturers being able to increase servicing schedules ::)
....and inserting expensive, time-consumming & profitable cam-belt changes into the shedules!!
;D ;D
Tbh, I think it's swings and roundabouts.. there are pro's and cons of each. but I think going back to the original Q, the reason for implemenging OHC engines is because they are mroe capable of delivering the power and efficiency that the market requires..
What does that do for society & our Carbon-Footprints??
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.......As James said, pushrod engines have chains too. .......
Unless it's a Ford Essex/Cologne V6. They use gears, originally one of them was fibre, for quietness, however they had a tendancy to be very quiet when the fibre gear shed its teeth and the engine stopped! ;) :y
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Interesting points... but not having oil immersed timing chains has contributed towards car manufacturers being able to increase servicing schedules ::)
....and inserting expensive, time-consumming & profitable cam-belt changes into the shedules!!
;D ;D
Tbh, I think it's swings and roundabouts.. there are pro's and cons of each. but I think going back to the original Q, the reason for implemenging OHC engines is because they are mroe capable of delivering the power and efficiency that the market requires..
What does that do for society & our Carbon-Footprints??
OHC has much better control over the valves and allows variable cam timing (and even lift) which is important for start-up emissions and balancing power and efficiency.
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As James said,
James hasn't posted on this thread - he is outside cleaning out the car ::) ::) ;D
Who is James & why has he not posted anything??
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As James said,
James hasn't posted on this thread - he is outside cleaning out the car ::) ::) ;D
Who is James & why has he not posted anything??
His arms are too sore. Cambelts and bruises from SWMBO. ::) ;D
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oooooh ! big mistake assuming a chain will never break, i had one go on a 16 valve merc 190, it were'nt cheap ! old skool v enginge's are the safest in this aspect i suppose, no chain or belt but 2 gears running directly off each other, rover v8, ford essex and so on, i remember reading somewhere that it was fiat who invented the timing belt, not sure though anyone know ?
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As James said,
James hasn't posted on this thread - he is outside cleaning out the car ::) ::) ;D
Who is James & why has he not posted anything??
His arms are too sore. Cambelts and bruises from SWMBO. ::) ;D
So are mine - 4 hours of playing Melodeon last night for a Ceilidh!
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oooooh ! big mistake assuming a chain will never break, i had one go on a 16 valve merc 190, it were'nt cheap ! old skool v enginge's are the safest in this aspect i suppose, no chain or belt but 2 gears running directly off each other, rover v8, ford essex and so on, i remember reading somewhere that it was fiat who invented the timing belt, not sure though anyone know ?
Depends on whether it is driven sensibly I suppose! :-?
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In the past I've had a few carlton gsi's and a senator all with timing chains and all I can say is 12 valve works 24 valve doesn't. and just like when the cambelt goes the engine's going to its grave.
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oooooh ! big mistake assuming a chain will never break, i had one go on a 16 valve merc 190, it were'nt cheap ! old skool v enginge's are the safest in this aspect i suppose, no chain or belt but 2 gears running directly off each other, rover v8, ford essex and so on, i remember reading somewhere that it was fiat who invented the timing belt, not sure though anyone know ?
Depends on whether it is driven sensibly I suppose! :-?
;) hehe, it was'nt being ;)
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Before my Mig i had a Rover 800 Diesel & that runs a very reliable VM engine, no belt, no chain, just cogs= nothing to change, snap or pull.
If the Rover was easier to get parts for i wouldn't have changed, but i do love my Miggy just as much even though down on power compared to the Rover.
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oooooh ! big mistake assuming a chain will never break, i had one go on a 16 valve merc 190, it were'nt cheap ! old skool v enginge's are the safest in this aspect i suppose, no chain or belt but 2 gears running directly off each other, rover v8, ford essex and so on, i remember reading somewhere that it was fiat who invented the timing belt, not sure though anyone know ?
Depends on whether it is driven sensibly I suppose! :-?
What, like idling while parked? :-?
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I never recall having seen a failure of an engine in a Motor cycle or Car, failing because of a push-rod problem or failure!
So - why do we now have over-head camshafts, & perhaps
more critically, camshafts driven by rubber-bands?
Seems to me that if you do have to have OHC, that chain driven are more reliable/ economical to maintain (e.g. Traktors, Nissan Micras) than these wretched belt-driven lumps (unless of course they provide a good excuse for a Beery weekend get-together for readers of the ultra-right Daily Mail!)
Discuss :-?
Micra's are well known for breaking the chain, and just generally wearing out the chain and tensioner system soon. Nissan claimed it was because the oil wasn't being changed enough, but....... I guess like all systems, it depends who's designing/making it.
Ken
P.S., its a pain to change the chain or tensioners on the micra.
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Its a mith this chain super reliabilty thing, there not, they streth and wear (as you would expect).
I ahev known quite a few of the 6 cylidner diseasels to suffer chain problems, on these the tensioner normlay wears and the pump umps a tooth.
And the driver behind over head cam, performance.
To get good high rev ability you need to be able to have a controlled valve opening AND closing.....and by having an over head cam you have a light valve train which gives you this.
Compare this to a puch rod where you have possibly a hydraulic follower (although some dont), push rod, rocker, valve....to get good high rev ability you end up fitting big valve springs to shut the valves fast and all because you have a large mass of valve train to move!
Now, thats a very small reason why!
My personal preference is for a belt as they are quiet and because you service them regulalry, they are a known item where as chains are very much unknown....
Gm however, are moving there engines back to chain setups....
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Cambelts, on a plus point, are MUCH easier to replace than a timing chain (which pushrod engines also have!)... and cambelts are also reliable if changed on schedule.
Given all the pro's and cons, I would rather change a rubber belt every 40k miles, than have to struggle to do a timing chain every 100k....
The question was rhetorical (& I was not anticipating serious answers)
But in answer to your point, who ever needs to change a timing chain apart from those who patently ignore servicing schedules to the point of crass negligence, & would not the same people cheerfully miss the recommended cam-belt change intervals too?
Yep probably very true.
Chains are known to stretch over time and the guides tend to break up around 100K.
Poll? How many Traktor owners on the forum have had to replace a timing chain?
I'm at 140K currently
Remember, poor oil servicing accelerates the wear on the chain, so keep to those 3k oil changes!
The likely value of car and the huge amount of labour (head off, sump off (which I think may mean engine out)) means the car gets written off instead....
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Its a mith this chain super reliabilty thing, there not, they streth and wear (as you would expect).
I ahev known quite a few of the 6 cylidner diseasels to suffer chain problems, on these the tensioner normlay wears and the pump umps a tooth.
And the driver behind over head cam, performance.
To get good high rev ability you need to be able to have a controlled valve opening AND closing.....and by having an over head cam you have a light valve train which gives you this.
Compare this to a puch rod where you have possibly a hydraulic follower (although some dont), push rod, rocker, valve....to get good high rev ability you end up fitting big valve springs to shut the valves fast and all because you have a large mass of valve train to move!
Now, thats a very small reason why!
My personal preference is for a belt as they are quiet and because you service them regulalry, they are a known item where as chains are very much unknown....
Gm however, are moving there engines back to chain setups....
You can have cams high in block with short push rods.
I have had a pushrod car engine up over 7200 rpm and it came off cam
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Its a mith this chain super reliabilty thing, there not, they streth and wear (as you would expect).
I ahev known quite a few of the 6 cylidner diseasels to suffer chain problems, on these the tensioner normlay wears and the pump umps a tooth.
And the driver behind over head cam, performance.
To get good high rev ability you need to be able to have a controlled valve opening AND closing.....and by having an over head cam you have a light valve train which gives you this.
Compare this to a puch rod where you have possibly a hydraulic follower (although some dont), push rod, rocker, valve....to get good high rev ability you end up fitting big valve springs to shut the valves fast and all because you have a large mass of valve train to move!
Now, thats a very small reason why!
My personal preference is for a belt as they are quiet and because you service them regulalry, they are a known item where as chains are very much unknown....
Gm however, are moving there engines back to chain setups....
You can have cams high in block with short push rods.
I have had a pushrod car engine up over 7200 rpm and it came off cam
Never said you couldn't, but, you need big springs and that adds strain and high wear rates. On a push rod you idealy wouldn't run high lift cams, you would use the rocker to get your gain.
You also end up running multiple springs in order to overcome resonance issues to!
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It was running a Kent fast road cam, yes there was multiplication from the rockers, but the head did also have a 60 thou skim.
I met one chap who used to run to 8000rpm
And anything above poverty spec had twin valve springs.
My only problem was I reved a pool car with a long stroke 1300 to valve bounce thinking little engine - plenty of revs - not realising it was alot longer than my old 1600.
I just wish I had a die grinder - grinder bits in a drill in my bedsit was quite awkwards
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid... Take a look and the old bristol engine as used in the AC Ace before Carol Shelby molested it.
OHC engines main reason in racing is to reduce the reciprocating masses, there are no push rods or rockers to accelerate/decellerate on each cycle, as for the production engine this can't hurt, but the OHC design also significantly reduces the number of parts that need to be made and thus makes the engine cheaper to build. Hoever and SOHC design either has to have the valves all in a row (like the 8V engine) which is not so good for gas flow, ideally you want inlet and exhaust valves each side of the head, this can be done, but you can either add a set of rockers, as BMW and Triumph did (truimphs version being as woudl be expected a far more elegant solution!) or add a second cam.
Stewart
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As James said,
James hasn't posted on this thread - he is outside cleaning out the car ::) ::) ;D
Who is James & why has he not posted anything??[/quote]
Jamesv6cdx thats who he is and the reason he not posted anything was he was out side cleaning his car pitchfork ;D
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No offence intended, however things probably got a tad confused when accidental use of Maria/JamesV6CDX profiles.........
May possibly avoid confusion if you double check when posting technical type responses?? ;)
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Given that we share the sams PC at home, I must admit, when Maria leaves her account logged in, I will often sign onto the forum and reply to posts, before I realise I am logged in as her ;D
When it became apparent that I had answered something technical using her account, we just made light hearted fun of it - joking that she must have learned so much at the cambelt party that she was able to answer :D -but the responses were really from me :y
I must admit I've not seriously followed this thread, but I'll have a more thorough read tomorrow, and if I need to address anything, I will :y
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Given that we share the sams PC at home, I must admit, when Maria leaves her account logged in, I will often sign onto the forum and reply to posts, before I realise I am logged in as her ;D
When it became apparent that I had answered something technical using her account, we just made light hearted fun of it - joking that she must have learned so much at the cambelt party that she was able to answer :D -but the responses were really from me :y
I must admit I've not seriously followed this thread, but I'll have a more hthorough read tomorrow, and if I need to address anything, I will :y
Thanks.
As you appreciate, not every viewer of the community has spoken to you both in person and, by use of both profiles when posting, it gives confused messages. Those who have met you both in person can seperate the two differing persona in the typed word but others will struggle. Maria has thus become an instant expert!! ;D
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid...
Remember - each to their own - and amicable debate is good :)
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
As per Mark's post, it is down to personal preference. Now I have gained (some) experience, my preference is a belt which is relatively simple to change :y
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid...
Remember - each to their own - and amicable debate is good :)
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
As per Mark's post, it is down to personal preference. Now I have gained (some) experience, my preference is a belt which is relatively simple to change :y
Bring back Mr Fords original sidevalve..... Everything was so much simpler then...... ;D
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid...
Remember - each to their own - and amicable debate is good :)
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
As per Mark's post, it is down to personal preference. Now I have gained (some) experience, my preference is a belt which is relatively simple to change :y
Bring back Mr Fords original sidevalve..... Everything was so much simpler then...... ;D
Having said that, I am following a Mark1 Ford Escort Estate on ebay with genuine interest ::) ;D
My grandad used to tell me of fun removing the collets on side valve engines... he rekoned it was a lot simpler when I showed him an OHC head from my Veccy Z18XE!
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Some Desmodromic I.C valve-train systems do away with belts, chains and valve springs; with those (and many more engineering and operational advantages) why aren`t they more popular? :-?
Bevel-Desmo-Animation: http://www.bevel-enthusiasm.com/image/parts/bevelanime.mpg
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Some Desmodromic I.C valve-train systems do away with belts, chains and valve springs; with those (and many more engineering and operational advantages) why aren`t they more popular? :-? ......
Have you never heard a Ducati? They sound like a bag of spanners. ;D :y :y
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Have you never heard a Ducati? They sound like a bag of spanners. ;D :y :y
;D ;D ;D ;D ;D ;D ;D ;D
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid... Take a look and the old bristol engine as used in the AC Ace before Carol Shelby molested it.
OHC engines main reason in racing is to reduce the reciprocating masses, there are no push rods or rockers to accelerate/decellerate on each cycle, as for the production engine this can't hurt, but the OHC design also significantly reduces the number of parts that need to be made and thus makes the engine cheaper to build. Hoever and SOHC design either has to have the valves all in a row (like the 8V engine) which is not so good for gas flow, ideally you want inlet and exhaust valves each side of the head, this can be done, but you can either add a set of rockers, as BMW and Triumph did (truimphs version being as woudl be expected a far more elegant solution!) or add a second cam.
Stewart
Not totaly correct either, its not a reciprocating mass you are reducing, it the valve train weight.
In addition, with SOHC there are simple ways of offsetting the valves and again the GM 4 pot is a good example with a hydraulic lifter at one end of a rocker, the valve at the other and the cam working on the upper surface....
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The other important factor in reducing the valve train weight and using a 1:1 ratio of cam lift to valve lift is that the cam wears a lot better.
Because everything wears slower, and there are much fewer moving parts an OHC setup is almost maintenance free whereas a pushrod setup will always need adjustment - you have the tappets themselves, their interface with the pushrods, pushrod to rocker, rocker to shaft, rocker to valve stem. Wear in any of these will affect the clearances on a pushrod setup.
There are some advantages. It's much easier being able to keep the engine timed up when you're taking the head on and off, such as when checking clearances, for example. Then again, it's a pain when you need to tweak the cam timing. :-/
I'm not sure anyone has ever made a 100% reliable cam drive. Chain, belt and gears all have their faulure modes. Maybe we should go to using vertical driveshafts and bevel gears like the old aero engines had?
One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir? 8-)
Kevin
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.
Rolling road setup helped immensly
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.
Rolling road setup helped immensly
If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......
To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either.... ;D
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Some Desmodromic I.C valve-train systems do away with belts, chains and valve springs; with those (and many more engineering and operational advantages) why aren`t they more popular? :-?
Bevel-Desmo-Animation: http://www.bevel-enthusiasm.com/image/parts/bevelanime.mpg
Cost & complexity - it took a young engineer called Massimo Bordi to develop a 4v version. He ended up getting a job at Ducati
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.
Rolling road setup helped immensly
If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......
To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either.... ;D
But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.
As to valve guide wear - can't see why they would wear much worse than any rocker type system.
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.
Rolling road setup helped immensly
If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......
To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either.... ;D
But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.
As to valve guide wear - can't see why they would wear much worse than any rocker type system.
Modern OVC setups dont have rockers at all so its a nice direct up down motion on the valve....
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?
I personally feel that OHV is old hat.
That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.
Rolling road setup helped immensly
If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......
To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either.... ;D
But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.
As to valve guide wear - can't see why they would wear much worse than any rocker type system.
Modern OVC setups dont have rockers at all so its a nice direct up down motion on the valve....
OK with twin cams but not so good on stuff like the Austin Rover O & S series.
DOHC actually makes it easier to design a head - just took a long time to become popular in cars, multivalve engines were common on bikes years before cars.
But then I have done the tappets on a 16v head with twin cams and 8 small forked rockers - Suzuki design.
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OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
Rubish I am afraid... Take a look and the old bristol engine as used in the AC Ace before Carol Shelby molested it.
OHC engines main reason in racing is to reduce the reciprocating masses, there are no push rods or rockers to accelerate/decellerate on each cycle, as for the production engine this can't hurt, but the OHC design also significantly reduces the number of parts that need to be made and thus makes the engine cheaper to build. Hoever and SOHC design either has to have the valves all in a row (like the 8V engine) which is not so good for gas flow, ideally you want inlet and exhaust valves each side of the head, this can be done, but you can either add a set of rockers, as BMW and Triumph did (truimphs version being as woudl be expected a far more elegant solution!) or add a second cam.
Stewart
Not totaly correct either, its not a reciprocating mass you are reducing, it the valve train weight.
In addition, with SOHC there are simple ways of offsetting the valves and again the GM 4 pot is a good example with a hydraulic lifter at one end of a rocker, the valve at the other and the cam working on the upper surface....
It is totally correct, the rockers and pushrods are all reciprocating masses. All the other parts are there on both OHV and OHC. By introuducing a rocker you have added a reciprocation mass, and lost some of the advantage of the SOHC design. Although Mercedes did it on the M110 DOHC engine.
Stewart
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Q: Overhead cams , why??
A : they're bloody uncomfortable to sit on.
I miss my Duplex Chained Straight 6 :(
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One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir? 8-)
Kevin
Damn i thought that was my invention ;D - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait ;D ;D ;D :y
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One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir? 8-)
Kevin
Damn i thought that was my invention ;D - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait ;D ;D ;D :y
Problem is the forces required to accelerate the valves are considerable, and not easy to achieve with a solenoid. Some sort of electro-hydraulic setup might work, but it would be very expensive compared to a lump of cast iron with some lobes ground on it, and has the potential to be less reliable.
IIRC it's been played with by someone - one of the F1 teams perhaps (where the problems are compounded by very high revs).
Edited to say: Cam and crank sensor reliability achieved by VX would really ruin your day too as you'd have mangled valves as well. :o
Kevin
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Too technical for me, bring back the side valve. :y :y :y
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One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir? 8-)
Kevin
Damn i thought that was my invention ;D - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait ;D ;D ;D :y
It is being worked on - it may even be used in test cars
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One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir? 8-)
Kevin
Damn i thought that was my invention ;D - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait ;D ;D ;D :y
Problem is the forces required to accelerate the valves are considerable, and not easy to achieve with a solenoid. Some sort of electro-hydraulic setup might work, but it would be very expensive compared to a lump of cast iron with some lobes ground on it, and has the potential to be less reliable.
IIRC it's been played with by someone - one of the F1 teams perhaps (where the problems are compounded by very high revs).
Edited to say: Cam and crank sensor reliability achieved by VX would really ruin your day too as you'd have mangled valves as well. :o
Kevin
I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts
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I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts
I think whatever system of actuation is used will be quite power hungry though. The biggest advantage will be a continuously variable cam profile dependant on speed and load - so you can have the holy grails of good low down torque, bonkers high red line and economy when you're not hoofing it. 8-)
Kevin
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I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts
I think whatever system of actuation is used will be quite power hungry though. The biggest advantage will be a continuously variable cam profile dependant on speed and load - so you can have the holy grails of good low down torque, bonkers high red line and economy when you're not hoofing it. 8-)
Kevin
If electrical powered - run the alternator only when braking, free power.
I reckon there are a few places to get free power from. Oil pump, water pump, valve train. Could help an F1 car quite a bit.
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
weren't early Saab's 2 stroke, sounded like wet farts ::)
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Some Desmodromic I.C valve-train systems do away with belts, chains and valve springs; with those (and many more engineering and operational advantages) why aren`t they more popular? :-? ......
Have you never heard a Ducati? They sound like a bag of spanners. ;D :y :y
thats because they use a dry clutch,but the desmodromic valvetrain gives much more control over valve movement,hence an engine which revs higher and produces more power than you would expect from a v twin 8-)
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
There have been several successful 2 stroke cars ... Saab did them for many years.
http://www.motorbase.com/engine/by-id/948549497
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
There have been several successful 2 stroke cars ... Saab did one for many years.
http://www.motorbase.com/engine/by-id/948549497
irrc didn't it win the RAC rally back when it was a proper rally
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
i think they produce plenty of power but not much torque,ok an a bike but no use pulling the weight of a car.omissions would also be a big problem these days.
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
not a clue but i do know they cost a packet to rebuild
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
not a clue but i do know they cost a packet to rebuild
Its neither as there is not stroke because its a rotary action and its also difficult to determine the cc as its a swept area.......had an RX7 which I nearly set fire to because I parked it on some dry grass and the ceramic exhaust gets rather hot!
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
;D ;D ;D
Well, somebody had to. ::) ::)
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
;D ;D ;D
Well, somebody had to. ::) ::)
:o ....and it would be me woudn`t it? ::)
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
i think they produce plenty of power but not much torque,ok an a bike but no use pulling the weight of a car.omissions would also be a big problem these days.
With modern technology I'm sure that emission issues would be easily solved & if the torque was so bad, how come the Saabs of old were good enough to win rallies???
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What about he Trochoidal-Wankel rotary engine (RX7/8); is that 2 or 4 stroke? (or maybe it`s neither)
A mate of mine has one in a Westfield. On the brief occasions when it works, it's louder idling than mine is at full chat. ;D
Kevin
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
i think they produce plenty of power but not much torque,ok an a bike but no use pulling the weight of a car.omissions would also be a big problem these days.
With modern technology I'm sure that emission issues would be easily solved & if the torque was so bad, how come the Saabs of old were good enough to win rallies???
I would have thought direct petrol injection would help 2 stroke engines get back into favour. After all, the main problem with them is that the fuel saunters into one port and out of the other unburnt and makes a real mess of the emissions. If you inject fuel after the ports have closed it should work much better. :-/
Kevin
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The large 2 stroke diesels I used to work on were direct injection with a pushrod inlet valve and ported exhaust to a tuned exhaust pipe feeding a turbocharger...
Only real problem was the two metre stroke length.... Would need a large bonnet bulge to accomodate it in a car, methinks. ;)
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2 stroke Diesels are interesting - I personally like Napier D18s
18 cylinders 36 pistons 3 cranks found in pairs in Britains most powerful Diesel loco
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The large 2 stroke diesels I used to work on were direct injection with a pushrod inlet valve and ported exhaust to a tuned exhaust pipe feeding a turbocharger...
Only real problem was the two metre stroke length.... Would need a large bonnet bulge to accomodate it in a car, methinks. ;)
I think the shock absorbers would take a bit of a battering too!
Could mount it fore-aft horizontally like an ond tractor and watch it rocking back and forth at the traffic lights!
Kevin
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2 stroke Diesels are interesting - I personally like Napier D18s
18 cylinders 36 pistons 3 cranks found in pairs in Britains most powerful Diesel loco
Heavenly sounds on rails: A Deltic......or 2nd. a Brush-Sulzer 47 'wide-open'....(Sighs!) 8-)
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Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?
i think they produce plenty of power but not much torque,ok an a bike but no use pulling the weight of a car.omissions would also be a big problem these days.
With modern technology I'm sure that emission issues would be easily solved & if the torque was so bad, how come the Saabs of old were good enough to win rallies???
I would have thought direct petrol injection would help 2 stroke engines get back into favour. After all, the main problem with them is that the fuel saunters into one port and out of the other unburnt and makes a real mess of the emissions. If you inject fuel after the ports have closed it should work much better. :-/
Kevin
i think it is possible,but bimota bankrupt themselves trying to perfect a system to pass the emissions regs. :-/
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Off on a slight tangent can anyone tell me how variable valve timing works? :-/
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2 stroke Diesels are interesting - I personally like Napier D18s
18 cylinders 36 pistons 3 cranks found in pairs in Britains most powerful Diesel loco
Heavenly sounds on rails: A Deltic......or 2nd. a Brush-Sulzer 47 'wide-open'....(Sighs!) 8-)
Sulzer - they are OK but not a patch on a EE 16CSVT
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Best sounding Diesel power units - together - also happens that both are express passenger and 100mph capable.
Deltic & 50 (http://uk.youtube.com/watch?v=ve1Jl9gOiLA) double heading
50 doing the work (http://uk.youtube.com/watch?v=AP96__VpwSM&feature=related)
Deltic doing the work (http://uk.youtube.com/watch?v=3gLKUrjblOE&feature=related)
SOme of these clips are not good
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2 stroke Diesels are interesting - I personally like Napier D18s
18 cylinders 36 pistons 3 cranks found in pairs in Britains most powerful Diesel loco
Heavenly sounds on rails: A Deltic......or 2nd. a Brush-Sulzer 47 'wide-open'....(Sighs!) 8-)
Sulzer - they are OK but not a patch on a EE 16CSVT
Were they used in Class 50`s?
I also really like the 'exhaust-whistle' of the EE used in the Class 40`s :y
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Off on a slight tangent can anyone tell me how variable valve timing works? :-/
Just as it says. It's a system that alters the point in the crankshaft rotation where the valves open and close.
The theory is that, if you have a fixed relationship between the crankshaft angle and where the valves open and close (as with most current engines) you can only tune the engine to work best over part of its' RPM range because the optimum valve timing (and lift) to achieve best power / economy varies over the rev range.
This is because it takes time to accelerate the gases that pass through the valves and they continue for a while once they are moving. Meanwhile, at higher RPM the engine cycle takes a shorter time so you generally want a proportionally longer duration of valve opening at higher RPM. In addition, resonance in the exhaust and inlet system can be used with a little overlap (both intake and exhaust valves open at once) to "pull" gases through the engine faster at high RPM.
If you go for a cam that gives you the greatest power at high RPM it will generally have a lot of lift, duration and overlap and will be lousy at low RPM (listen to a top fuel dragster idling sometime). At low RPM the engine is not capable of "breathing" as deeply, so you need less valve lift and duration to keep the speed of the gases high to ensure good "swirl" (mixing of air and fuel as they fill the cylinder), and overlap is generally a bad idea.
So, car manufacturers have always had a massive compromise in designing cams because, although customers want an engine that'll produce a high peak power and have a wide RPM range they also want something that has enough torque at 1500 RPM that they can pull away easily.
VVT is an attempt to get around this by changing the timing, sometimes just of the inlet cam and sometimes exhaust as well, and sometimes duration and lift as well as timing, in response to changing engine RPM. So, your engine has the cam from a Massey Fergusson at low RPM and when you hit the point at which that cam would run out of steam, it shifts a little bit further towards the top fuel dragster to give good high RPM performance.
That's the theory, anyway.
As always, Wikipedia is your friend http://en.wikipedia.org/wiki/Variable_valve_timing
Kevin