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[Webby the Bear]

No school today 

was typing steve 

[Marks DTM Calib]

Resonation is in the line of the valve (it cant occur at a right angle due to the valve guide).

Simple physics, a spring with a mass will have a resonating frequency which may be in the engine operating range ( e.g a specific rpm).

Add a second smaller spring inside the main one and design it so that it resonates at a different frequency and when one of them resonates, the other wont and hence you overcome the issue.

Or make the springs stronger and design them so they only resonate at very high rpms beyond the engine operating range, this is not good for pushrod and rocker engines as it results in larger components being needed (stronger) which increases the valve train weight.....which is not good as it limits the upper rpm range....thats a major advantage of OHC....lighter valve train 

Not totaly conviced on your torque talk...its the crank that converts a linear motion into a rotational one and hence its the crank where the torque is produced.

[Andy B]

.....
 ..... the spring keeps it closed and holds the valve shut until the next time the cam opens it. ....

Unless it's a Ducati & the valves are desmodromic 

[Webby the Bear]

Resonation is in the line of the valve (it cant occur at a right angle due to the valve guide).

Simple physics, a spring with a mass will have a resonating frequency which may be in the engine operating range ( e.g a specific rpm).

Add a second smaller spring inside the main one and design it so that it resonates at a different frequency and when one of them resonates, the other wont and hence you overcome the issue.

Or make the springs stronger and design them so they only resonate at very high rpms beyond the engine operating range, this is not good for pushrod and rocker engines as it results in larger components being needed (stronger) which increases the valve train weight.....which is not good as it limits the upper rpm range....thats a major advantage of OHC....lighter valve train 

Not totaly conviced on your torque talk...its the crank that converts a linear motion into a rotational one and hence its the crank where the torque is produced.

that makes sense re the resonating and the smaller spring inside the bigger one. however one thing i've obviously missed which i should have asked...... what's the actual problem with resonating? noise? worn parts? soz should have asked really.

as for the torque talk. as far as i know, yes, the crank is where the torque is ''given'' to the drive shaft, but its what happens in the combustion chamber and the acts and forces on the pistons that sends that power...... or have i got confused with the question? 

[Manual Elite V6]

Resonation is in the line of the valve (it cant occur at a right angle due to the valve guide).

Simple physics, a spring with a mass will have a resonating frequency which may be in the engine operating range ( e.g a specific rpm).

Add a second smaller spring inside the main one and design it so that it resonates at a different frequency and when one of them resonates, the other wont and hence you overcome the issue.

Or make the springs stronger and design them so they only resonate at very high rpms beyond the engine operating range, this is not good for pushrod and rocker engines as it results in larger components being needed (stronger) which increases the valve train weight.....which is not good as it limits the upper rpm range....thats a major advantage of OHC....lighter valve train 

Not totaly conviced on your torque talk...its the crank that converts a linear motion into a rotational one and hence its the crank where the torque is produced.

that makes sense re the resonating and the smaller spring inside the bigger one. however one thing i've obviously missed which i should have asked...... what's the actual problem with resonating? noise? worn parts? soz should have asked really.

as for the torque talk. as far as i know, yes, the crank is where the torque is ''given'' to the drive shaft, but its what happens in the combustion chamber and the acts and forces on the pistons that sends that power...... or have i got confused with the question? 

If I remember correctly when the springs reach a certain speed and are resonating at quite a high frequency the valve is in a sense just floating as the spring isn't making contact with the valves which eventually leads to the sudden contact when the resonance stops, which causes the valve to crash into the cam.

[Webby the Bear]

Resonation is in the line of the valve (it cant occur at a right angle due to the valve guide).

Simple physics, a spring with a mass will have a resonating frequency which may be in the engine operating range ( e.g a specific rpm).

Add a second smaller spring inside the main one and design it so that it resonates at a different frequency and when one of them resonates, the other wont and hence you overcome the issue.

Or make the springs stronger and design them so they only resonate at very high rpms beyond the engine operating range, this is not good for pushrod and rocker engines as it results in larger components being needed (stronger) which increases the valve train weight.....which is not good as it limits the upper rpm range....thats a major advantage of OHC....lighter valve train 

Not totaly conviced on your torque talk...its the crank that converts a linear motion into a rotational one and hence its the crank where the torque is produced.

that makes sense re the resonating and the smaller spring inside the bigger one. however one thing i've obviously missed which i should have asked...... what's the actual problem with resonating? noise? worn parts? soz should have asked really.

as for the torque talk. as far as i know, yes, the crank is where the torque is ''given'' to the drive shaft, but its what happens in the combustion chamber and the acts and forces on the pistons that sends that power...... or have i got confused with the question? 

If I remember correctly when the springs reach a certain speed and are resonating at quite a high frequency the valve is in a sense just floating as the spring isn't making contact with the valves which eventually leads to the sudden contact when the resonance stops, which causes the valve to crash into the cam.

that makes sense mate... and just thinking aloud, i imagine that if the valve is floating like that then it could in theory be open or closed when its not supposed to be hence affecting the 4 stroke cycle. perhaps 

[Marks DTM Calib]

Exactly, if the valve resonates then it does not close (it will still fully open as its being forced open but it relies on the spring to close it).

Interestingly, cams and psrung valves may weel dissappear soon, I was observing a Sulzer marine engine the other day with directly actuated valves.....i.e. electro-hydraulic.

This gives infinate timing, lift and duration control 

[Webby the Bear]

Haha don't boggle my mind Mark, i can only take so much info 

[Andy B]

..... marine engine the other day with directly actuated valves.....i.e. electro-hydraulic.

This gives infinate timing, lift and duration control 

I'm seen similar ideas before (on paper though & not in the metal) ...... It never seems to make it to the road though 

[albitz]

Pretty sure F1 cars have a similar setup.

Edit.
http://scarbsf1.com/valves.html

[f3nt0n]

I am ABSOLUTELY LOVING this thread. My foster parents owned a garage when I lived with them 30 yrs ago and I spent a lot of time there with my fosterdad. This stuff is exactly what he taught me when I decided to take apart broken old cars and put them back together again (for profit!) including minis, a jensen-healy, a renault 4 (bought for £250 with a blown head gasket (engine out jobbie, royal pain in the arse) -£75 for HG kit - sold it for £900! PROPER PROFIT in that old motor!), an mgb and a Rover p600. Incidentally, I absolutely loved working on the Austin "A" series engine, because it was so lovely and simple!

Thanks Web and looking forward to more...

[Webby the Bear]

glad you're enjoying it mate. Thanks for the feedback. It's great on here too cos there's so many knowledgeable folk on here to help out and chip in. I actually have a load of stuff ive got to self study so am hoping to give another update tomorrow :-) cheers mate :-)

[Webby the Bear]

Week 5 begins.

Evening gents, help/advice needed in red please 

Well today had the potential to be interesting until the entire class (minus myself) decided they were going to dick about like idiots all day and not get on with the work 
I find the guys mostly funny but there's overkill and they went past that today and the teacher saw red. Anyways.....

I did a cambelt on a SOHC Renault engine (Megane or clit, not sure which...). Well I don't think I've ever done something so simple....... Crank notch @ 6 o'clock. Cam sprocket @ 12 o'clock. Tensioner off. Belt off. We did some other stuff to the head that I'd already done and gone through on here (valve springs out, lapping in the valves with the grinding paste, reattach the head etc etc).
Anyway, cam sprocket and crank sprocket both at their respective timing notches/marks. belt on, feed tight up the right hand side (as you look at it) belt over the cam sprocket, tensioner back in, tighten tensioner up. PIECE OF P...!

So that was enjoyable and half way through we were shown compression testing 
Real simple..... if you got a 4 pot you would do 4 ''Dry'' tests and 4 ''Wet'' tests. I'll explain.

1.) Isolate the fuel system... pull fuel injectors out or simply pull the Fuel Pump fuse out 
2.) Isolate the spark... pull the HT leads out, take the spark plugs out and disconnect the distributor/coilpack.
3.) Break out this bad boy...

you fix it to the correct attachment that's the same size as your spark plugs and then screw it in to pot one for the first of the ''Dry'' tests. Turn engine over a few times and the dial above will score your first reading. Repeat for 3 other pots.
4.) Time for ''Wet'' testing. Let's keep it simple. Pot 1 we'll imagine we got a dry reading of 165. We then pour some oil down the spark plug well. this will cover the top of the piston. plug in our compression tester. Turn engine over and record our reading. if its the same or only slightly above our initial ''dry'' test reading then our pot is good for compression. if on our wet test we get a reading thats 40+ above our initial dry test reading (so a reading of 205 upwards) then our pot is losing compression.....
We know this because the oil we poured in has sealed where our compression leak is and hence given us a higher reading. If we had no compression leak in the first place the oil would make no (or very little difference).

Sadly i'd only just got through my dry test on pot 3 when my class decided to turn in to a load of immature retards and we were all told to pack away early in preperation for a 30 minute bollocking!  seriously i really dont see why i should have to pack up what i'm doing cos some little tw*ts can't stop honking the car's horns!!!  i and a few others genuinely want to learn!!!

Rant over. Actually no it's not...

The tutor did also go through a ''Leak Down Test''. Again this was doomed from the off..... there's two leak down test gauges available. Both used by some moronic children who used them without setting them back to zero before reusing. this broke them  this is simply tested by not plugging it in and getting a reading from the fresh air.... ours in the fresh air was saying we had no leak 
So I presume we'll have to wait for a new one to be ordered 

If you're wondering what the difference is between a compression test and a leak down test..... ask someone else cos i wasn't told! lol i can't understand what the difference is because the compression test will measure air pressure in the cylinder and you perform the wet test to see if there's leaks..... the leak down test will also find leaks. at a guess i'd say the leak down test would be more foolproof. Anyone care to clarify?

So if this day wasn't a tad mental anyway, halfway through the tutor's rant he chucks in a load of formulas. now i'm sad that he did this. i'm not the best at maths  and i like to take my time when given an equation.

HOWEVER. i'm going to post this now and show this as ''today's lesson''..... and expect another post in a few minutes about cylinder formulas and you can hopefully tell me if i've managed to grasp it. 

oooooh one last quick thing..... We measured a cylinder head for warping  so easy...... get a flat edge, place it on the head (combustion chamber side).... can you get the smallest feeler gauge in between the head and the flat edge tool.... yes? you hae warpage and it needs to be machined. no? your head is not warped. proceed 

[omega3000]

Nice work , shame about those knuckle heads spoiling it 

[Webby the Bear]

Mechanic School Blog After Hours 

CYLINDER FORMULAS & VOLUMES

SWEPT VOLUME a.k.a ''STROKE'' VOLUME a.k.a DISPLACEMENT a.k.a ENGINE LITRE SIZE
This quite simply is the volume covered by the cylinder from it's upper most point (TDC) to it's lowest most point (BDC):

Swept volume formula is: Pi X radius squared X the stroke.
EXAMPLE: if the diameter (or bore) of your cylinder is 80mm and your stroke is 70mm the calculation would be: 3.14159265359 X 16cm X 7cm = 352cm3.............X4 cylinders = 1407cc (1.4L Engine  )

CLEARANCE VOLUME (The volume of the Combustion Chamber)
This, again quite simply, is the area from TDC upwards which is basically the combustion chamber. Difficult to measure when you think that usually the combustion chamber is hemospherical (if thats even correct  )
See this diagram and the crude white marked out area with the purple star.... its late, ok? 

Clearance volume formula is: Swept Volume / Compression Ratio - 1.
EXAMPLE: From the example before... one cylinder = 352cm3 / 8:1 - 1 = 7. 352/7 = 50.285cm3

COMPRESSION RATIO
This is the combustion chamber volume expressed as a ratio compared to the swept volume.
Compression Ratio Formula is: Swept Volume + Clearance Volume / Clearance Volume
EXAMPLE: Our pot on this shite 1.4L engine is has a swept volume of 352cm3 + 50.255cm3 = 402.26cm3 / 50.285cm3 = 7.999........... Compression Ratio of 8:1 

Right guys, this is seriously enough maths for today. I hope I've got all the above correct but if I haven't please do correct me... I need to learn.

I'm a bit pee'd off I've had to research this myself when I should have had it taught to me in class but due to the stupidity of what turned out to be the majority 

Well that is rant over.

Hope you enjoyed the detail but I doubt it as I know it's a bit... errrrm.... tedious 

over and out until tomorrow my dawgs

Car Bear.