Scott,
High crankcase pressure, assuming you have some type of functional PCV
system, is the result of poor piston ring sealing. Either there are many
miles on the lower end of this engine or something has deteriorated the
sealing quality of your rings, in one or all of the cylinders, prematurely.
I would suggest starting with a compression check of all the cylinders. Make
sure they are reasonably close to one another and original specification. I
usually use plus or minus 5% as a start to worry threshold. e.g. at 150 psi
you should see no more than a 15 psi cylinder to cylinder deviation. Do the
check with the engine warm. A better check for ring integrity is to use a
leakdown gauge. This measures, I think volumetric based, percentage leakdown
for each cylinder. Keep in mind both of these measurement techniques are
also giving you a glimpse of valve seat/sealing integrity. The last
technique for measuring blowby is by sealing all crankcase vents and using a
flowmeter, ball in a sight glass, to watch how much compression is making it
by the rings. Don't mis-diagnose.
Your blue smoke could be coming from a variety of sources. Straight off I
would say with high crankcase pressure that the smoke is due to oil getting
by the rings, however, this can be a what came fist the chicken or the egg
scenario. You may have poor compression ring(s) but a good oil ring. In this
case oil may be being pushed through the PCV system into the intake manifold
and burned. This can be determined by using some sort of push pull bottle in
the PCV circuit. A push pull bottle is similar to a compressed air dryer.
Essentially there is a bowl which will catch the oil and not permit it from
reaching the intake manifold. Another cheaper but less convincing method is
to vent the crankcase to atmosphere and check for your blue smoke.
Finally make sure your PCV system is working. Many people overlook this as a
waste of time. I have easily seen a few horsepower by reducing crankcase
pressure and therefore windage. Low crankcase pressure will help your oil
pan gasket leak but will not help oil leaks from pressurized galleys etc..
Have fun.
Regards,
Matthew Van Benschoten
mvb@voyager.net
http://my.voyager.net/mvb
-----Original Message-----
From: HD883HUGGR@aol.com <HD883HUGGR@aol.com>
To: spitfires@autox.team.net <spitfires@autox.team.net>
Date: Friday, October 22, 1999 12:29 PM
Subject: Excess Crankcase Pressure (formerly: header & related smell)
>
>Hi List: I think I sent this directly to Joe by mistake. Any assistance
>will be appreciated.--
>
><< Scott, Ask me why that sounded so familiar! I did a write-up on how to
> correct the problem of crankcase pressure and it is on Tom Shirley's
> Spitfire Garage Tips archive. I hope it helps you out! Joe >>
>
>Joe: With all the dupe messages lately, I'm afraid my response to your
above
>message might have gotten lost in the sauce.
> I think you're right on target with your hypothesis regarding
>over-pressurized crankcase, because I have also noticed oil ON TOP of my
>ribbed aluminum valve cover, which apparently is coming from the oil filler
>cap. So how do I find Tom Shirley's Spitfire Garage Tips archive?
> Next question: a buddy who proclaims to be a mechanic says the
>over-pressurized crankcase may be shooting oil into the carb, which may be
>the cause of the rather large amount of blue smoke coming from the exhaust
>tips. Prior to the recent work (where ZS & stock intake manifold were
>replaced with a Weber & a Cannon intake, and the stock exhaust manifold &
>pipe were replaced with a header & monza exhaust -- and ERG valve was
>subsequently removed), I did not notice any blue smoke from Hobbs at all.
> Will driving the car in its current condition do any damage (other than
>pollute the atmosphere)? Will decreasing the crankcase pressure resolve or
>help resolve this blue smoke problem? And maybe even decrease the increase
in
>oil leak from my oil pan gasket?
> Thanks, Joe -- or other mechanically inclined Spitphiles -- for your
>assistance and advice.
> Scott (& Hobbs, fire-breathing 77 Spit)
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