Is there anyway to truly tell the source of low compression in a specific cylinder, is it valve or rings, how can you tell?

run a compression test on all cylinders...plugs pulled, throttle wide open etc.

note numbers then


add alittle oil into cylinders, re-run test and note numbers.

if it goes up alot then its rings as the extra oil will seal the rings.

if its the same its valves

Dooohhhh! I knew that, I hate it when your memory lets you down, I guess I killed to many brain cells in my youth! Thanks for the kick to my memory !

There is a little debate on how accurate this is for engines with a horizontal layout. (It doesn't seem to work well for some people?) A leak-down test will tell you about individual valves, and about how the rings seal at TDC.

...It's another option, at least!

--DD

It just a way to get a read on the situation.

Get a leakdown test if you can. By listening for where the air hisses you can get a good idea where the problem is. In my case using a vacuum hose down the oil filler pointed to air leaking past the rings. You can listen down the intake for air leaking past the intake valve and up the exhaust for the exhaust valve. I suppose you might be able to hear a leak at the head too but, I don't know that for sure. It's really kind of a fun test.

Dave