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Glow Engine Smoking After Running

Old 05-20-2020, 12:24 AM
  #1  
Andrewmc
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Default Glow Engine Smoking After Running

I have recently rebuilt a saito FA 56 after a long hiatus - essentially replaced the bearings, stripped and cleaned everything and reset clearances etc.
I mounted it in a test bed for the first run and ran it rich for a tank just to get everything nicely lubbed. Second tank I adjusted the HS needle to a running setting (around 9000rpm). Transition from idle to WOT was good and I cycled this a few times and then switched off.
After the engine had stopped there was "smoke" coming off the exhaust manifold. The cylinder was not too hot as I could touch it. I have noticed this before and had thought that the setting might be too lean, but I do not think that the engine is currently set too lean.
What else would cause the smoking? Note that this is not smoke coming out of the exhaust but more rising from the outside of the manifold and exhaust silencer.
Old 05-20-2020, 06:44 AM
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tedsander
 
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Probably a small bit of oil burning off the outside of the silencer. There might be a small leak in the manifold/silencer connections. Or it may just be fine droplets coming from either the exhaust itself, or even the carb, being deposited and then starting to "cook". (the air currents around the engine can get really complex!) Does your silencer have a pressure fitting? That too could be the source of the oil - either leaking, or if open, just allowing unburnt exhaust to exit that way, and get on the outside of the silencer. Depending on how you fill your tank, if you do have a pressure line coming off the silencer, and remove it to fill the tank, it could just be a drop or two that got on the outside while filling.
BTW - one of the big purposes of oil in the engine is to assist in carrying heat away, so it doesn't burn much in the combustion chamber. Hence why one has to clean their craft after running.
Of course, you may be running the engine too lean...but if it passes the touch test, that is less likely.
Likely not a big issue - keep an eye on it, and while you may get a little bit of brown coating over time, it shouldn't be much.
Old 05-20-2020, 06:50 AM
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Andrewmc
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Originally Posted by tedsander View Post
Probably a small bit of oil burning off the outside of the silencer. There might be a small leak in the manifold/silencer connections. Or it may just be fine droplets coming from either the exhaust itself, or even the carb, being deposited and then starting to "cook". (the air currents around the engine can get really complex!) Does your silencer have a pressure fitting? That too could be the source of the oil - either leaking, or if open, just allowing unburnt exhaust to exit that way, and get on the outside of the silencer. Depending on how you fill your tank, if you do have a pressure line coming off the silencer, and remove it to fill the tank, it could just be a drop or two that got on the outside while filling.
BTW - one of the big purposes of oil in the engine is to assist in carrying heat away, so it doesn't burn much in the combustion chamber. Hence why one has to clean their craft after running.
Of course, you may be running the engine too lean...but if it passes the touch test, that is less likely.
Likely not a big issue - keep an eye on it, and while you may get a little bit of brown coating over time, it shouldn't be much.
Thanks tedsander, I will monitor it after flying, but all makes sense.
Going into winter here in the southern hemisphere could also just be good old moisture in the air.


Old 05-20-2020, 09:29 AM
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the Wasp
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I have not heard of this before. you should ask on the Saito page, those guys are Saito Freaks.

Welcome to Club SAITO !

Jim
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