Compression comes from the top rings on the pistons. The bottom ring is the
oil control ring. You can have good compression and have bad rings. Engines
using oil will sometime have great compression because the oil provide a
better seal for the compression rings.
If you replace the rings, you need to clean the ring grooves on the pistons,
hone the cylinder walls, and stagger the rings. There will be some oil usage
until the rings are seated. Oil consumption from new rings should disappear
after 500-1000 miles.
Smoke from valve stem seals usually occurs when the engine is first started
and disappears after the engine is run for a few minutes. The smoke comes
from oil running down the valve stem after the engine is stopped or after a
downshift where the throttle is closed and the oil is sucked down the valve
stems. If the valve to valve guide clearance is correct and the valve stem
seals are OK it will likely be a ring issue.
The above answer is based on a stock 948 that is using oil. A later model
that is equipped with a PCV valve can suck oil it out of the engine if the
PCV valve is not working correctly resulting in oil smoke.
Also, you need to make sure the oil is good. If you have had a really rich
running engine, you could have gasoline contaminated oil which will leak
past the rings. Pull the dipstick and smell the oil, if you don't smell
gasoline, you will probably have to re-ring the engine.
Jim
-----Original Message-----
From: spridgets-bounces at autox.team.net
[mailto:spridgets-bounces at autox.team.net] On Behalf Of Gregory Groiss
Sent: Friday, July 01, 2011 11:05 AM
To: spridgets at autox.team.net; ROBERT MANIACI
Subject: [Spridgets] 948 With A Bad Smoking Problem
Hello All,
I am posting this for Bob Maniaci. He's tried to post it twice but I
never saw it show up on the list.....
Hey Guys
I'll run the scenario by you guys and maybe someone can help. I bought
my wife a '59
948cc bugeye for her b'day, car came from Fla. via Texas. The bugeye
was blowing alot
of smoke and oil coming out of the exhaust. I got a new 12G295 head and had
new
valves(3 angle grind)springs, bronze guides, and seals installed, Greg
Groiss and myself
removed the old head installed the new one( and found out that the
bugeye has .020 flat
top pistons)after installation 3 we did another compression test and
came out w/ the
following #'s cyl.#1 160, #2 155, #3 150, #4 150 reinstalld the plugs
and fired her up.
Immediately a plume of smoke shot out of the exhaust and got
progressively worse. Is it
possible the smoke is from residual oil in the exhaust. or is it
possible w/even those
compression #'s I have ring problem or something else I'm missing? If
it's the oil in the
exhaust pipe/muffler is there a way to to clear it without running the
car and having it
look like J. Bond switching on the smoke? (LIke seafoam) Any hlp or insight
is
appreciated
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