[f-AA] Short spark plug

[Ken Lessard]

Hello Bill in NH,
  In regards to your compression loss I would like to offer a past experience I had and maybe it can benefit you . There a several possibilities for the loss of compression, the worst being a cracked exhaust valve or burnt valve seat so I will share mine with you and this group. This is a cut and paste from a topic I responded to on the Aeronca L3 site recently. I only post it here for your consideration and not, by far, a recommendation. It's just something that worked for me a long time ago... I also came up with a way to ream the exhaust valve guide on my friends C-172 with an 0300, that had a history of sticking exhaust valves, without pulling the jug...That's another story in itself...   Ken in MA

 "Hi John,
I was just wondering if you determined where your compression loss
was coming from during the leak down test. Years ago I had the same
problem with my C-75 engine in my Ercoupe. My #1 cylinder was 55/80
and my IA friend suggested that I make a determination where the
loss was before ripping into the engine. With the cylinder
pressurized with air I took off the oil cap and listened, no sound
so the piston and rings are good. Next I put my ear to the carb.
intake, no sound so the intake valve was good. Lastly I put my ear
to the exhaust and heard lots of air rushing. Hmmm, seems to be a
bad exhaust valve. Way back then, the only fuel option was 100ll. 80
octane was gone and mogas was not legal yet so we had major problems
with lead deposits in the cooler running cylinders. Now, hang on
because I'm gonna tell ya what I did to fix it (under direction from
the IA). I pulled the air filter and cowl and ran the engine up to
temp. We brought the engine up to 1800 RPM and sprayed atomized
water into the carb. inlet using a pump type garden sprayer. Very
little at first and increased the volume of water until the engine
started to loose RPM. I was stunned to see all the black crap that
belched out of the exhaust. I did this two times and the second time
the exhaust was clear. The next compression test #1 was up to 77/80
and all the cylinders came up to 76/80 to 78/80. I'm not
recommending this procedure but it sure worked for me. The
compression stayed up through the next 4 annuals until I sold the
plane.. Just a thought... Ken"
 
  ----- Original Message ----- 
  From: Bill<mailto:wbeauv at metrocast.net> 
  To: aeronca at westmont.edu<mailto:aeronca at westmont.edu> 
  Sent: Wednesday, November 01, 2006 5:54 PM
  Subject: [f-AA] Short spark plug


  Hi.We are doing our annual on Moya (1946 7AC) and the IA I'm working with said I should put the Short plug in the front cylinder.Can someone tell me the numbers for it and a good supplier for an A65.I've got one cylinder reading low (45/80) and we can hear the air coming out the exhaust.The others all read 71/80 and have about 500 hours on them.He seems to think the valve is sticking becouse I run mostly pump gas and don't use(sorry to start any wars ) MMO.We're going to run the motor to warm it up and check again.Has anyone else ran into this problem before. Thanks. Bill in N.H. 2505E
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