RE: compression woes

[Jim Grammer <jimg@domain.elided>]

I
>My '72 Scout II (V345, auto) has developed a serious lack of
>compression, but only in the two frontmost cylinders (1 and 2).
>Number 1 shows about 90 psi, number 2 is only good for 72.
>
>Squirting about a tablespoon of oil in number 1 raises the
>pressure to about 160, but it takes about 3 times that much
>oil in number 2 to get a mere 130 psi.

 I'd guess #1 has worn rings, but #2 has also either a broken compression 
ring or a valve not quite seating or both.


>The rest of the cylinders are all between 145 and 160. So far
>as I know the engine is stock, with stock compression, 8.28/1.
>
>How credible is the oil test to distinguish leaky rings from
>leaky valves?

Pretty good, and time tested to boot. You could also do a cylinder leakdown 
test. 'Nother possibility is an aggressive combustion chamber cleaning(I 
have 'seen' mineral spirits used to good effect, heard ATF is effective) to 
get rid of the carbon in the equation. Don't do this unless you really want 
to know how worn everything is, and be ready to change the oil soon 'cause 
it'll be full of tiny carbon bits.

>If the test is credible, what are the odds that a clean, well
>maintained 345 will wear out its rings in 157k miles?

Not unheard of, that's for sure.

>If anybody's gone down this road before please share your story!
>I don't want to tear the engine down needlessly, but neither do
>I want to break anything, especially a valve!

I'd be surprised if you broke anything by continuing to drive it, tho' the 
performance will suffer and she may smoke some. Basically, if you're gonna 
work on it soon, I'd dig deeper now. If not, I'd keep oil in it and drive 
until I was ready to pull the motor.

Jim