<VV> Advice on Rings (was Help - Oil Out Dipstick Tube)

[Tony Underwood]

At 10:21 PM 9/8/2010, Jay Pitchford wrote:

>The PCV system was clear. A compression check was done, and it showed
>145-150 lbs on three of the six cylinders. Two of the other three
>showed ~90 lbs,


That's pretty low...


>and one was ~65 lbs.


That's WAY too low.


>One bank ... the one reading two cylinders low ... was smoking a bit,
>but our thought was maybe the rings were still seating. I drove it
>carefully, generally 3500 revs or less, but never over 4000 while
>upshifting. The mild Isky cam had 5k miles on it already, so that
>wasn't a concern.


Are all the low cylinders on the same bank, or is one low cylinder on 
the opposite bank?


>48 hours and 150 miles after picking it up, I started it and blew
>clouds of oil smoke out of the bank, the one that was slightly smoking
>earlier. Temp stayed normal; no oil light; no clatter other than a
>slight valve tick expected before the hot adjust. I'm convinced I just
>blew one of my brand-new rings, and I'm hoping it didn't score the
>brand-new full fin jug.


The low compression is a bit alarming for a fresh engine.   What do 
the cylinders test now, after some miles?


>Question: Is it possible to put a ring in 'backwards'?


Unless they're exotic compression rings, (Dykes rings etc) it's not 
gonna cause that much trouble.  They do have (or most do) a marker 
dot on them to indicate which side is "up", but it's not very likely 
to make THAT much difference if the compression rings are installed 
upside-down.   Depending on type, oil rings CAN be an issue but if 
they're the standard 3-piece oil rings (not the cast one-piece), they 
won't care.   They won't have much effect on compression anyway.


>If so, you
>figure a guy that doesn't know the difference would have a 50/50
>chance at it ... and I was reading low on exactly three cylinders
>after a ground-up rebuild.

Exactly what kind of rings are these?   Are the compression rings 
cast iron or moly-filled?  Cast iron rings can break VERY easily, 
while the moly-filled rings tend to be less brittle and will usually 
bend before they break.

When the pistons went into the cylinders, did they go in from the top 
or the bottom of the cylinders?    What sort of ring compressor was 
used?   This could be important...


...did you check clearances on the cylinders, just to be 
sure?   Three that low doesn't sound right at all.  Even before rings 
seat, you should have had more compression than what your low 
cylinders are showing, right after the first cranking and start-up 
with NO break-in at all, especially that one very low 
cylinder.   That one is only trapping a bit more than 4 
atmospheres... something went wrong there.   I wouldn't expect too 
much lower compression than 65 lbs if there were NO compression rings 
on that particular piston.


...what's the story on the cylinders?   Again, were piston clearances 
checked before assembly?   And were the cylinders prepped as they 
should have been?   You mentioned they were new... is that new as in 
NEW or are they fresh rebores?


>Any thoughts and/or advice would be appreciated.

The smoke speaks volumes.   If the heads are OK (you said M. LeV. did 
them so they should be fine) I'd not think the smoke would be from 
guide clearance... the guides would need to be worn pretty bad to 
make "clouds" of smoke on start-up but it's not likely they would 
cause such a difference in compression without other symptoms as in 
noisy valves if the guides were loose enough to allow the valve to 
wobble and not seat...    If the valves themselves were simply leaky, 
and causing the low compression, it still wouldn't cause smoking 
and/or blowby without the accompanying loose guides.    I'd suspect 
the heads are OK in this instance and I'd go with something wrong 
with cylinder sealing... smoke generally means bad ring seal or loose 
clearances, piston/cylinder or worn/cracked rings... which are in 
this instance new but if something went wrong, all bets are 
off.    The blowby kinda confirms that as well.   Low 
compression?   It speaks for itself... time for another compression 
check.   Something is wrong in those three holes.   I don't think you 
need to look at the heads.



By the way, whenever I have a pan off or an engine apart, when it 
goes back together I stick a #2 phillips screwdriver into the bottom 
of the dipstick tube where it extends down into the crankcase and I 
snap it off.   Then I "ream" out the bottom of the tube with the same 
screwdriver to make sure there's no burs or kinks.    The tube can 
stick down far enough to dip into the oil in the pan and if there's 
blowby the crankcase can pressurize enough to push oil up and out of 
the dipstick, if the engine is given any major throttle openings 
under load... even with a functioning crankcase vent system.

Check that compression again and let the group know what you find.



tony..