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Originally Posted by ludeguy1
I know what compression is and how it works, but my question is when you test it (which i have done to my 93 h23a1) is the number that you get...like 170...180.... the pressure(psi) at the compression stroke? I'm pretty sure thats what those numbers stand for.
Second question: ive been looking at h22's on ebay and some of them say they have been compression tested and LEAK DOWN tested or something like that. What is LEAK DOWN testing? what do they do in this process and what do the results stand for? Thanks for the input  |
yeah usually it is on compression stroke - because that is when all the intake and exhaust valves (for that cylinder) are closed at the same time (ie: it wouldn't make sense to do it on the exhaust stroke because the exhaust valves would be open!) how do you find compression stroke? usually by removing the spark plug - and putting your thumb over the hole - while someone manually turns the engine - when air is pushed out past your thumb - you should be on the compression stroke - saying that i imagine it's pretty hard to use your thumb on a prelude - haha, but yea anything to block the hole but so that you can tell when the air stops gushing.
you are correct about the numbers they are in psi - for a 4 cyl - you should get 4 of them.
as for a leak down - not completely sure about this one - so someone correct me if i'm wrong - but imagine they add the pressure to the cylinder and do a differential pressure test between the cylinder and say the exhaust manifold - that way they can tell if their is any "leak" by the difference in pressure. - It's great if a cylinder can reach 200psi - but for how long? how much leak? i think that's what they are getting at.
it's recomended that the engine is run before doing a compression/leakdown (heh impossible with floor sitting jdms) but that is just because a coat of oil could probably "increase" the sealing capability- so if anything the numbers should only get better then if it was dry-tested.
i've also heard that during a compression test you should open the throttle right up (just so you are taking that buttefly valve out of the equation if there is something wrong with one of the intake valves.
that's the way i see it.
hope that helps - and someone please correct me if i'm wrong.