Re: Compression test, hot or cold?
Sea-Horse is correct! A compression test is only a "reference" as to what compression is. It does not mean you don't have bad rings/cylinders, etc... Really, the key is to check all cylinders the same. You would not test one cylinder cold, run the engine and then test a different cylinder "hot", the next, with throttle closed, the next with the throttle open..... just do them all the same and the readings will be consistant. That's the baseline you are looking for! I just did a V-4 OMC motor and had 3 cylinders at 120 psi and one at 110 psi. The consensious, of him and I, was that 10 psi was probably ok, as the customer says he did not know of any "lack of power" the last time he used the motor! (It was in for a bad power pak, which he destroy'd by hooking up the battery backwards, Battery C.D. ignition, 1970, these motors do not like that very much) anyway, after I install'd the new pack, the motor ran like crap,but had ignition, which it didn't have prior, but I did two more compression checks and still had 120 and 110 all around, pull'd off the intake side cover and had stuck rings, scouring and aluminum seperation of that "low" piston, Guess what?? He thinks I SHOULD of known that the motor was toast prior to me installing the $370 pack and $30 coil!! I told him I (in good faith) did a compression check (and check'd the gear oil) to help prevent this exact conversation with him !! He and I both agreed that 10 psi probably wasn't cause for concern !! An educated guess on both our parts!! "But your're the "professional", you should of known!". I told him, I was sick the day in service school that the gypsy came and taught how to predict the future with her chrystal ball.(and her friend, Superman came that same day to show us how to fine-tune our X-ray vision to look internally for problems, too). And that I didn't feel he should "monday morning quarterbacking" this and use it to blame me for his engine problems! "If I'd known that the engine was bad I wouldn't have paid you, (me) to install parts that weren't going to help the engine run any better", "You should take off the parts You install'd, and not charge me a thing!!!" I told him he was mistaken, If I could know beforhand, what the problems with motors were prior to actually "working" on them, I would be down at lottery headquarters and not working on his 32 year old outboard !!! I am reluctantly taking off the pak, will put it in inventory but he is gunna pay some labor, frieght, etc... Anyway, forgive me from straying... A compression check really does not mean you don't have problems, it is just a helpfull tool to use in identifing potential problems. Have a good day!!
