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[Webby the Bear]

The valves may be open to some extent at the same time,but they wont be open at TDC.

Not on the power stroke but they will between exhaust and intake. Gas moving down the exhaust scavenges the cylinder much more effectively if the intake valve is already opening, and this also helps to accelerate the intake charge before the piston starts to move down the cylinder.

Thanks Kev so how come they dont hit the piston between the E and I strokes? 

Well, they're not fully open. Exhaust valve is closing and intake valve is opening at this time, and the clearance between valves and piston is carefully worked out.

cheers mate, was just wondering 

[aaronjb]

The valves may be open to some extent at the same time,but they wont be open at TDC.

Not on the power stroke but they will between exhaust and intake. Gas moving down the exhaust scavenges the cylinder much more effectively if the intake valve is already opening, and this also helps to accelerate the intake charge before the piston starts to move down the cylinder.

Thanks Kev so how come they dont hit the piston between the E and I strokes? 

Well, they're not fully open. Exhaust valve is closing and intake valve is opening at this time, and the clearance between valves and piston is carefully worked out.

Or if you're feeling ghetto, checked with some plasticine.. 

[Kevin Wood]

Or if you're feeling ghetto, checked with some plasticine.. 

True.

Or the seat of the pants if you're running hydraulic tappets.

[aaronjb]

Or if you're feeling ghetto, checked with some plasticine.. 

True.

Or the seat of the pants if you're running hydraulic tappets.

Indeed, it gets expensive if you need to buy two sets just to fill some with wax..

[Webby the Bear]

afternoon chaps. Got some great stuff to share with the class. Going for a curry with Martin42 tonight as the northampton branch of OOF ha ha anyone in the area wants to go let me know. Anyway prob wont get an update chance today but will do tomorrow. Moved on to diesel today but before all that i have the interesting pug exhaust to go through. Lol it Wasnt pretty ha ha prob update tomorrow :-)

[Webby the Bear]

Afternoon fellas...

Well bit late with the update for this weeks' blog but as Im now on half term for two weeks  i didnt see the point in rushing 
However, there's a lot to cover. so let's start at the beginning

SPARK PLUG WEAR:
Image of a spark plug with normal wear... brown or grey colouration at firing end:


Image of a spark plug with white ''crusty'' deposits at firing end.... plugs have overheated probably due to use of plug with incorrect heat range:


Image of spark plug with carbon fouling due to over rich fuel mixture... any idea why the mixture could get over-rich???


Image of spark plug with oil fouling.... due to worn bores and/or piston rings or worn valve guides. this also can occur temporarily during the running in period:


Image of spark plug with blistered white deposits (difficult to differentiate between this and the crusty one in my opinion) ...... caused by worn valve guides, excessive use of upper cylinder lubricant, or idling for long periods.


Finally on spark plugs....
a SP that is worn through age/use will have an increasingly larger gap. the effect this will have...
weak spark could equal loss of power. also late spark could occur throwing the timing out. or finally it could cause no spark if it uses the cylinder head as the ''earth'' instead of the electrode due to the gap being too big.

DIESEL ENGINES AND FUEL SYSTEMS.....

This one i was particularly looking forward to as i knew nowt about diesels but they're suprisingly similar...

if we look at the four stroke cycle it's pretty much identical to that of the ''spark ignition'' (petrol) engine except the spark is replaced with fuelinjection....

induction:
only air pulled in... no fiel at this point.

compression:
the air is compressedd but to a much higher rate than a petrol engine... its usual that diesel engines have roughly double the compressin ratio to that of a petrol engine. at 10o before TDC (where the spark would occur in a petrol engine) the fuel is injected. due to the higher compression ratio the air is compressed and heated PAST the flashpoint of the diesel fuel. therefore when the fuel is injected it ignites.....

power:
diesel having self ignition temperature of around 400oC the diesel burns increasing the pressure in the cylinder and forcing the piston downwards.

Exhaust:
burned waste gas forced out of the cylinder as normal. it is also common for a diesel exhaust system to have a filter to reduce the carbon/soot build up.


......SHITE..... got to nip out - will continue update later today... there is lots! 

[Marks DTM Calib]

I doubt you will see such saprk plug issues on all but classic cars these days.

The only real issues you get now are wear (electrode recession) and sometimes fouling, all thanks to monster ignition voltages, knock control and mixture feedback control.

Diesels are simple, very simple.....more interesting once common rail comes into the equation but, sill pretty simple be it small single cylinder units or very large x00 litre jobs.

 

[Nick W]

Or if you're feeling ghetto, checked with some plasticine.. 

True.

Or the seat of the pants if you're running hydraulic tappets.

Indeed, it gets expensive if you need to buy two sets just to fill some with wax..

Why would you buy two sets when you only need to check one cylinder for clearance? Something you could quite easily do with the old followers that you won't be using.

[Webby the Bear]

Evening chaps, as mentioned before still on half term which is why the updates aren't coming through everyday.

I've still got some stuff to update on diesles what I've learned so far but there's not much to be honest.

HOWEVER my homework is cool 

I have to research the use of Turbos and Superchargers 

Now from what I've learned already the turbo is connected between the exhaust manifold and exhaust pipe. The exhaust gas coming out of the manifold goes in to the turbo and turns a turbine. at its maximum heat it gets to 959oC and at its fastest UNBELIEVABLY 240,000RPM!!!! no, i didnt mistype that!!! I mean wtf!!!!!
Anyhow... this turbine is connected to an air compressor by way of a small shaft (lubricated by engine oil).
Air is pulled in by the rotating compressor, errm, then compressed and connected to the inlet manifold where the compressed air is forced in to the cylinders.
More air + more fuel = more power 
to get more power you would have to increase cubic capacity and normally you'd have to chuck in some more cyliners or make them bigger whatever... but this would perhaps not be practical and would also add weight. the turbo is a space and weight saving device giving increased power using the exhaust gases which exist already... kind of killing two birds with one stone 

This is a turbo.... labelled by moi:



Also worth noting that when you compress air it increases temperature (the whole point of the afore-discussed compression ignition (diesel) engines where the air is compressed increasing the temperature to past the diesel fkashpoint...diesel injected... BOOM) so between the turbo and the cylinders (part of the intake i believe) would be an intercooler to cool the air down prior to it being sucked in to the cylinders.

SO this prompts an interesting question........ what's to stop one of us dweebs fitting a turbo? and has anyone done it? and if not possible why not?

Anyway thats the basics. got a lot more to research on these but got excited so i thought id update 

 

[Marks DTM Calib]

There is much more to it than just blowing air in.

As you are now producing more energy, you produce more heat and that heat has to be dealt with by the cooling system. More power also means more strain on the bottom end and drive train and hence this often needs beefing up to.

Further to this, you need to lower the static compression ratio as the dynamic one will be higher in, this means new pistons.

Very expensive to convert an engine to be blown

[Webby the Bear]

thanks mark :-) i didnt think about the effect on other components. What interested me was how the compressed air stays compressed between compressor and cylinders ? I know nothing in depth bout physics but would have thought that once in the inlet it would be allowed to expand again.

[Marks DTM Calib]

It would only expand if allowed to e.g. if the pipe work gets bigger.

Not all vehicles have/had intercoolers, some diesels had no intercooler, other petrol engines use charge cooling (e.g. the Lotus Caarlton) where a fine water mist is sprayed into the inlet to cool the air.

Many supercharged engines dont use intercoolers, some use charge cooling, some nothing.

[Omegatoy]

It would only expand if allowed to e.g. if the pipe work gets bigger.

Not all vehicles have/had intercoolers, some diesels had no intercooler, other petrol engines use charge cooling (e.g. the Lotus Caarlton) where a fine water mist is sprayed into the inlet to cool the air.

Many supercharged engines dont use intercoolers, some use charge cooling, some nothing.

CHARGE COOLER is a self contained unit, which cools the inlet temps by heat transfer to the water held in the charge cooler,
it does not inject water into the inlet,thats water injection!! totally different ballgame Mark

[aaronjb]

Technically doesn't it all really just come under the heading of "charge cooling" whether it's air/air (commonly 'intercooler') air/water (commonly 'chargecooler') or water injection? Seeing as all three achieve the same aim - cooling the intake charge.

As an aside, you don't always need to do lots of expensive stuff to turbocharge an engine - take the little Toyota 1ZZ-FE; relatively high static compression ratio of 10.5:1, fully floating liners, peened rods but no other fancy components, even a plastic intake manifold, and it'll happily take ~10-12psi of boost to increase the crank hp from ~140 to ~300 before the bottom end lets go. In fact, the gearbox usually eats itself before the engine..

Even the 2ZZ-GE with it's even higher static compression ratio of 11.5:1 has been turbo- and supercharged without mods, though (naturally) it won't stand as much boost pressure.

Not everyone makes chocolate engines like Vauxhall *ducks*

[Omegatoy]

Technically doesn't it all really just come under the heading of "charge cooling" whether it's air/air (commonly 'intercooler') air/water (commonly 'chargecooler') or water injection? Seeing as all three achieve the same aim - cooling the intake charge.

As an aside, you don't always need to do lots of expensive stuff to turbocharge an engine - take the little Toyota 1ZZ-FE; relatively high static compression ratio of 10.5:1, fully floating liners, peened rods but no other fancy components, even a plastic intake manifold, and it'll happily take ~10-12psi of boost to increase the crank hp from ~140 to ~300 before the bottom end lets go. In fact, the gearbox usually eats itself before the engine..

Even the 2ZZ-GE with it's even higher static compression ratio of 11.5:1 has been turbo- and supercharged without mods, though (naturally) it won't stand as much boost pressure.

Not everyone makes chocolate engines like Vauxhall *ducks*

lol only the v6 is made of choccy!11
water injection is there to cool the incoming charge agreed, but its used mainly to stop detonation on high turbo boost levels,