Plug replacements for O-360-A3A

Hey all... awhile back I posted querying on spark plug replacements, but I
have no actually looked at the plugs I currently have. I thought they were Champions,
but they're actually Auburn ER400 SR-88. From the chart he
http://tinyurl.com/arqcv (warning: PDF at lycoming)
those plugs should not be used in an O-360-A series engine. Presumably, that's
because it's high-compression, and the SR-88 is a hot plug. Strangely, apparently the
REM40E is the equivalent Champion plug, which *is* approved in the A-series.

I've pretty much decided to go with the Autolite plugs, but now the question
is which one. I run autogas (93 AKI) in it usually and have seen no ill effects from
the hot plugs and marginal octane rating save one: When returning from a flight on
autogas, if I try to shut down the engine with the mags, it will diesel. I was
worried until I checked a friend's Cherokee-150 with low-compression.... definately
NOT marginal for octane rating It dieseled under the same conditions.

So, I haven't had any fouling problems or any indication of detonation in
flight. I've looked at the pistons through the plug holes, and just a nice thing
carbony layer. Should I go with a colder plug, or put in the Autolite equiv of what's
in there (UREM40E)?

-Cory

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************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

No engine can diesel without a fuel source... If it is dieseling, it is
getting fuel... If it is getting fuel then the mixture rod is not
cutting the fuel flow off completely... If the mixture is not cutting
off properly then your carb needs a rebuild... Res ipsa loquitor...
As far as the heat range, go with the recommended plug in whatever
brand you like... If the current plugs are hotter than recommended
either he was having lead fouling problems, or oil fouling problems...
Or he got a heck of a deal on the plugs...

denny - who's engines do not diesel on mogas...

After going with regular spark plugs for 1500 hours, I switched to fine
wire plugs. They are better. I get lead deposits around the base of the
plug, but they start anyway. I can go 500 hours without a cleaning,
though I wouldn't recommend it. Also, from what I have heard, they last
virtually forever. Just be careful with the sandblaster, they are
delicate and an agressive sand blast could destroy them. They are
expensive, but worth it. No more spark plug cleaning except at annual
now.

OK... my original post wasn't clear on the dieseling. It doesn't *normally*
diesel... only when I shut it off with the mags. Of course, I rarely do it, but I
discovered it one time when I tried. I was initially disturbed by it, but if you
think it though, it's a pretty tough situation to keep the fuel from igniting. Very
hot cylinders, very low RPM means very high MP even at idle setting. At the dieseling
RPM (100 or so), the MP will go up to 25", even with the throttle at idle. That
means essentially "full throttle," but a 5-10x longer *time* than idle RPM to
encourage the fuel charge to ignite. Actually, compared to takeoff RPM, more like a
25x factor longer time.

Anyway, I've decided to go with the midrange plugs (UREM38E). If they foul,
I'll clean them more often and/or change them back to hotter.

-Cory

Denny wrote:
: No engine can diesel without a fuel source... If it is dieseling, it is
: getting fuel... If it is getting fuel then the mixture rod is not
: cutting the fuel flow off completely... If the mixture is not cutting
: off properly then your carb needs a rebuild... Res ipsa loquitor...
: As far as the heat range, go with the recommended plug in whatever
: brand you like... If the current plugs are hotter than recommended
: either he was having lead fouling problems, or oil fouling problems...
: Or he got a heck of a deal on the plugs...

: denny - who's engines do not diesel on mogas...


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************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************