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

Fri Sep 10 00:00:15 EDT 2010

Jay, Tony is right. Normally, the type of oil control ring is a spring with
two steel "rings, one on top and one on the bottom, kinda hard to mess that
up. But I do beg to differ on the compression rings. They are not
symettrical, (hence the dot) and have to be installed correct or they will
not provide compression as well nor will they scrape oil down on the down
stroke to let the oil control rings grab it to prevent too much oil smoking.

However, as much as you are having problems, I would suggest methodically
pulling that bank apart to find the culprit. Since the low compression is on
one side, you may have actually got oversized cylinders, a plus ten piston
in a plus 20, type of thing and it would be difficult to measure. And if the
mechanic has not had any problems with his supplier, he may not be as
vigilant in checking all of the measurements before assembly.

As a side note, I fixed a brand new Thunderbird which had a rod knock right
off the delivery truck with 2 miles on it (Yes, I hang my head low, I worked
in a Ford garage for awhile). One journal on the crank had been undersized
by - .010, probably due to a flaw in the rod journal and they didn't want to
throw the crank away, and the engine guys had to install what they were
given. I put a minus 10 bearing in that hole and life was good.

So, just be methodical and check everything, you will find it. No
guarantees, but if those cylinders are using that much oil, you probably
won't have any damage to the cyl walls. Just make sure the cyl bore and
piston sizes are matching!

Mark Durham

On Thu, Sep 9, 2010 at 12:10 AM, Tony Underwood <tony.underwood at cox.net>wrote:

> 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..
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