kapitanemo

hi dwight, there are about 54K miles on the car!

LeonV

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.

SouthDakotaS2K

You need to pressurize the cylinder while at TDC. Doing that will give you an indication where the "leak" is. A valve holding tool works well for this. A leakdown tester will work as well, but they usually operate at a lower regulated pressure that makes it difficult to pinpoint sometimes.

kapitanemo

thank you for the info! so oil in the chamber can help determine if its a piston ring problem, if determined to be a valve seating problem (whether bent, burnt, valve guide) is this something that you just have to pull out and see? and then if it is faulty can you just drop a new one in? (at the proper height of course). or is it like changing a piston ring where measurements and boring needs to be done?

SouthDakotaS2K

If you pressurize the cylinder while it is at the top on the compression stroke you can then listen for the leak. For example if you pressurize it and you hear hissing from the intake or throttle body there is a good chance you have an intake valve issue. Either bent, burnt or hanging. Same goes for the exhaust. If you hear it from the oil filler cap it can indicate bad rings as well, however there will always be a small amount that passes by the rings.

kapitanemo

got it. are valves straightforward to replace? like do you just swap them out with the new ones or is there additional work that needs to be done for them to work properly? assuming i have a bent/burnt valve

Billman250

Restraint is not easy here............................

Premise of a leakdown test: determine WHERE the leak is going. Not just "you have a leak".

Not knowing that is like telling you that you have CEL codes, but not telling you what the codes are.

Your valve adj could 100% be the problem if the valves have tightened to zero clearance.

starchland

Mechanic doesn't want to mess with it while under warranty? Is this his thinking maybe?

kapitanemo

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

kapitanemo

and I do acknowledge that the TAK or the paper jumping higher is counter-intuitive to a low compression stoke. but probably the stroke outputs are out of sync and causing the amplitude of one stroke's compression wave to increase.