[xk-engine] Blow by?

In reply to a message from KeithB sent Tue 20 Mar 2007:


I would add. It is extremely important that the engine builder get
the cylinder walls right. It takes a proper honing tool to get the
classic cross hatch marks. Some mistakenly use a simpler ‘‘glaze
buster’’. Sometimes the latter works and sometimes it doesn’t.

A compression test is a very good idea, open throttles, wet and
dry. That will tell you a lot.

Next and better is a leak down test. You insert the hose, pump up
the pressure. and close the valve. Watch the guage for the rate of
leakage. Usually found in performance store catalogs. Harbor
Freight probably has one or Summitt.

There are compounds to introduce into the oil to break the wall
glaze and allow the rings to seat and stop leaking. Some say they
work. They are an alternative to a tear down. I have my doubts.

Of course, unless you have oil puddles on the garage floor, it is
going into the combustion chamber in some fashion.

As Peter suggests, it may be a matter of over fill.

A classic break in was run the engine up on the RPM’s for a blast
then back off. Repeat several times. The back off is to allow oil
to be sucked in and lubricate & cool things down a little.

The original message included these comments:

It has been mentioned I think that getting the compression
rings to seal can be a problem. For running in, my engine
builder suggested short bursts of wide open throttle up to
4000 rpm with the engine well up to temperature - usually at
least 10 miles, to increase the pressure against the
compression rings and help the seat.
You have convinced me not to get my oil tested though…
Ignorance is bliss!

Carl Hutchins
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In reply to a message from cadjag sent Tue 20 Mar 2007:

Hi-- Thank you Keith for jarring loose the memories of those good
ol days before the oil analysis. Pure bliss!!!
Peter–When I first discover JL a hot topic disscussed overfill.
Since, I’ve been running on an 8 qt fill. The dipstick level falls
about 1/8’’ below the crossmarks warmed up. I know I’m low when it
approaches the tip. Only the head was worked on so far, nothing
done by me below that. Also, though I get a little smoke that does
not clearly indicate a bluish color on accel, since I rebuilt the
decel valves (ZS carbs) and learned how to adjust them, there is no
visible smoke on over run.
Keith–The wet test gives me 170-175 psi on all. This is just over
a 10% loss and said to still be in acceptable limits, though this
fact was the trigger when the blowby factor was introduced to my
brain. It seems a 10% loss is quite substancial to me.
Carl–The block has yet to have work done, unless it was the PO,
but with the history I have, this seems unlikely. I plan on a
leakdown test as soon as the weather breaks. I’ve just heard about
its value as an indicator. Thanks

My learning curve of interal combustion engines is getting steeper
than my dizzy’s advance curve.

Thanks — John–
John Deren
New Jersey '69 2+2, United States
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