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1. 09:01 PM - Detonation (Roger Kemp M.D.)
2. 11:52 PM - Re: Detonation (Frank Stelwagon)
Message 1
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All,
I have an enigma with my 50. Changed the #1 and #3 cylinders after finding I
had a compressions in the 30's on those two cylinders. All others were 76 to
78's. Tried staking them to no avail. Found that I had a bad valve guide on
#1 and a leaking valve on #3. Replaced them with two rebuild cylinders with
new pistons that included oversize rings. After reinstallation of the
cylinders have developed a detonation that was severe enough to stake the
elements on the fore and aft NGK spark plugs down onto the electrode
effectively grounding them out. Figured it was caused by an induction leak
after getting advice from the local gerus. Replaced the intake seals on the
intake tubes. Found I had the #1 seal leaking. Anyway runup was uneventful.
On lift off had a single misfire but climb out was uneventful. Inflight mag
check at 70% and 700 mmHg was 3% on both mags. Pushing the power up to 100%
for 3 to 5 seconds rewarded me with a misfire followed by an irregular
running engine. Pulling the RPM back to 70% smoother it out. Landing was
uneventful as was the runup for Sumping the engine. After shutting down did
a laser temp check that showed the #1 as the hottest cylinder at 145 deg C.
all of the others were in the 120's except for #6. It was 75 deg C. Pulled
the plugs on 6 and found the element closed down onto the electrode similar
to the previous runup where the elements were closed on the #1, #1 and #4
cylinders. The elements on those plugs looked like they had been hammered
down. OAT at 3500 ft was 85 deg.F. CHT on #4 was 180 and Oil temp was 58
deg C. right at the bottom of the yellow arc when the detonation began.
Surface temp was 95 deg F.
So, do I still have an induction leak leaning it out or what? The first
time, the #1, #3 and #4 front and rear plug were effectively grounded out
after the detonations occurred during runup at 70%. Put another set of new
plugs in gapped at 25/1000ths which is where the plugs are set from the
factory. When the initial round of detonation occurred, I had new plugs in
also but they were gapped at 20/1000ths. Remember #1 and #3 were the
cylinders replace in which their intake tubes had their gaskets / Seals
replaced.
What am I missing? I'm about ready to pull the new cylinders off and start
over!
Doc
Message 2
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I have seen ground electrodes blown off the spark plugs from detonation
but never hammered down. I have seen plugs hammered down from parts
(screws etc.) in the cylinders. In a normally aspirated engine the
parts can move from cylinder to cylinder, but I don't see how that would
happen in a supercharged engine. Could be detonation but it would be a
severe case.
CJ6-A N23021
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