compression and leakdown results
03-15-2013, 01:16 PM
#21
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Low compression in one cylinder is very likely a valve-sealing problem. When doing a leak-down test, you should be able to tell where the leak is happening, e.g. if you hear air escaping through the exhaust, it's an exhaust valve leak.
A valve check/adjustment wouldn't hurt and could very well be the cause of the lower compression. Tight valves will show lower compression. Check/adjust and hope that too much damage hasn't been done. Your mechanic's stubborness is unwarranted.
A valve check/adjustment wouldn't hurt and could very well be the cause of the lower compression. Tight valves will show lower compression. Check/adjust and hope that too much damage hasn't been done. Your mechanic's stubborness is unwarranted.
just an update everyone. first thank you for your inputs, I really appreciate it.
'mechanic' as I have been referring to him is not affiliated with the dealership I bought it from. mechanic is pushing for a full valve job as he is convinced its a burnt/bent valve and wants me to convince the dealership to have him do it etc. hes reputable and alot of you recommended him but Im having a really hard time dealing with him. I even asked him if he can help me adjust the valves or at least re-do the leakdown to determine where the seepage is coming from (like Billman suggested) but he, with no bad intentions, says 'dont have the dealership fix it they will do a crappy job' etc. 'insist on taking the car back or having them pay me to do it'. i get what hes saying but i just dont think i can make that idea fly.
took it to another s2000/NSX expert my uncle recommended. he's a cool guy and I highly recommend him. on the phone he said its just probably a tight valve. when i pulled up, even before i got out of the car, he yells to keep the engine running. when i step out hes already behind the car holding a sheet of paper mat to the muffler. the sound and pattern of flapping was arrhythmic! tak-tak-TAK-tak. i dont know if that makes sense to you guys. but the TAK is from the paper jumping higher than the rest then slapping back harder on the muffler. he checks compression on the alleged cylinder and it still reads low. he and his apprentice are convinced its just a tight valve. I think hes right mainly because im not throwing any CELs and I do think a burnt/bent valve would be more obvious. yes that paper-to-muffler test accentuated the symptom: the out of sync compression stroke, but without it that low compression stroke is not really detectable. whereas a burnt/bent valve, i believe, would be noticeable.
also this mechanic seems a lot more reasonable and that makes me trust his judgement more.
now my plan is to get the dealer to adjust the valves for me under warranty... hopefully its not going to be too much tooth pulling
'mechanic' as I have been referring to him is not affiliated with the dealership I bought it from. mechanic is pushing for a full valve job as he is convinced its a burnt/bent valve and wants me to convince the dealership to have him do it etc. hes reputable and alot of you recommended him but Im having a really hard time dealing with him. I even asked him if he can help me adjust the valves or at least re-do the leakdown to determine where the seepage is coming from (like Billman suggested) but he, with no bad intentions, says 'dont have the dealership fix it they will do a crappy job' etc. 'insist on taking the car back or having them pay me to do it'. i get what hes saying but i just dont think i can make that idea fly.
took it to another s2000/NSX expert my uncle recommended. he's a cool guy and I highly recommend him. on the phone he said its just probably a tight valve. when i pulled up, even before i got out of the car, he yells to keep the engine running. when i step out hes already behind the car holding a sheet of paper mat to the muffler. the sound and pattern of flapping was arrhythmic! tak-tak-TAK-tak. i dont know if that makes sense to you guys. but the TAK is from the paper jumping higher than the rest then slapping back harder on the muffler. he checks compression on the alleged cylinder and it still reads low. he and his apprentice are convinced its just a tight valve. I think hes right mainly because im not throwing any CELs and I do think a burnt/bent valve would be more obvious. yes that paper-to-muffler test accentuated the symptom: the out of sync compression stroke, but without it that low compression stroke is not really detectable. whereas a burnt/bent valve, i believe, would be noticeable.
also this mechanic seems a lot more reasonable and that makes me trust his judgement more.
now my plan is to get the dealer to adjust the valves for me under warranty... hopefully its not going to be too much tooth pulling
A bent or burnt valve will show zero or very low compression. A tight valve has MUCH higher chance of being the culprit of slightly lower compression in one cylinder.
A tight valve is an inadequately cooled valve, since the valve seat is what cools it. A tight exhaust valve would be the first to go as it gets much more heat than the intake valve.
The exaggerated exhaust pulse is caused by extra pressure in the exhaust, when compared to the other cylinders. I bet you have a tight exhaust valve (maybe intake too), because an earlier exhaust valve opening will release a higher pressure into the exhaust stream.
03-15-2013, 06:40 PM
#23
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03-18-2013, 07:34 AM
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dammit. so considering I have been running it with this tight valve, my valve has been eroded? should I look into a valve job?
Precisely. It will erode the valve until it no longer seals which equals zero compression in that cylinder.
Originally Posted by kapitanemo' timestamp='1363395236' post='22407081
thanks LeonV. so would this excessive heating of that one valve being tight eventually cause it to 'burn' or become a burnt valve?
03-18-2013, 10:10 AM
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03-18-2013, 10:23 AM
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Its gonna get a valve adjustment. The dealer/mechanic has a queue that I have to wait to die down before I can take it in. In the mean time I am thinking it through and evaluating scenarios. Not expecting to print something out off the internet, put it in my gas tank and have the problem poof away. That would be cool though 
03-18-2013, 01:05 PM
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Checking valves is not difficult; adjusting them does require a little proficiency but you don't need to do that just to ascertain if there is an issue. You pull the valve cover, buy an additional valve cover gasket if you want to play it safe, and get the proper tool for 10-20$. It's a good idea to replace your spark plug seals while you are in there as well IMO. They tend to leak in old hondas in my experience and you have to pull the valve cover to replace them and they cost ~1$.
03-22-2013, 09:25 AM
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update
brought it to dealership they re-performed the compression and leakdown test. results are
150 145 160 170 for the compression test
7% 17% 7% 4% for the leakdown test
vs (other readings at two diff mechanics)
230 190/200 225 230 compression test at mechanic 1
n/a 150 n/a n/a compression test at mechanic 2 (we only tested the suspect cylinder)
8% 40% 12% 5% for the leakdown at mechanic 1
sounds like the dealers numbers are sane. they said they cant do the valve adjustment under warranty because valve lash is a wear and tear thing, I tend to see their point. They also said that the compression is within spec (their spec is 135psi +/- 29psi) which I am skeptical about... 145 is 15% off from 170. Dealership readings as well as mechanic 2 readings were probably lower because not at WOT. Will bring to a mechanic soon to get it valve adjusted and hopefully compression and leakdown results improve.
What do you guys think of the 135psi +/- 29psi rule they have? is my 150 145 160 170 reading something to be worried about?
TIA
Niko
brought it to dealership they re-performed the compression and leakdown test. results are
150 145 160 170 for the compression test
7% 17% 7% 4% for the leakdown test
vs (other readings at two diff mechanics)
230 190/200 225 230 compression test at mechanic 1
n/a 150 n/a n/a compression test at mechanic 2 (we only tested the suspect cylinder)
8% 40% 12% 5% for the leakdown at mechanic 1
sounds like the dealers numbers are sane. they said they cant do the valve adjustment under warranty because valve lash is a wear and tear thing, I tend to see their point. They also said that the compression is within spec (their spec is 135psi +/- 29psi) which I am skeptical about... 145 is 15% off from 170. Dealership readings as well as mechanic 2 readings were probably lower because not at WOT. Will bring to a mechanic soon to get it valve adjusted and hopefully compression and leakdown results improve.
What do you guys think of the 135psi +/- 29psi rule they have? is my 150 145 160 170 reading something to be worried about?
TIA
Niko