compression test question

AJ/FormS said

So what do you consider acceptable?
I'll tell you my acceptable;on my guage. zero to 4% maximum.
You say; What! Hey I don't make stuff up. This is straight off the pages of Smokey Yunichs Power Secrets. A brilliant mechanic and racer of yesteryear.
At 8% that cylinder is toast. At 6% she is no longer performing anywhere near her potential.And bear in mind that a leakdown test is a snapshot of leakage at TDC only. From a few thou down,the cylinder could be split wide open, or the wrist-pin could have left a deep gash in the wall,and the gauge would still read A-OK. But at least you would know that the valves are closed. Likewise, the guides could be wore right out, or not even in there, but at least you would know that the valves are closed. The LD test is a snapshot. It's up to the tech to figure out the rest of the story.

Click to expand...

the yam definetly passed with low percentage on a fresh rebuildand lapped valves. The slant, probably around 6% or so. I was decently hhappy with it being a 45 year old engine. I did stem seals with my retired chrysler mechanic father. We noted no real play in the stems...but that's not a true tell obviously. But I did figure what you said could be happening. Either bore problem further down or sticky oil control ring. Who knows. Car runs darn good as it is and has plenty go highway legs so I haven't felt the need to pull the head yet. There was no alarming differences between cylinders when I had each one pressurized, so I never tested any other ones with the guage as it stands. One day...the head will come off. And I left it at that for meow.

30% !? **** an old bike engine I had had once cylinder leaking like that and it was a cold exhaust pipe !