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Exhaust gasket. OS 55AX

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Old 10-13-2019, 11:14 AM
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marthr
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Default Exhaust gasket. OS 55AX

I am getting back into glow aircraft after last dabbling 30 years ago. I have bought a new OS 55AX and am about to start running it in on the bench.

I was a little surprised to find there is no mention in the instructions of fitting any kind of gasket in between the head and the exhaust. There is a warning that *if* a silicone sealant is used care must be taken not to allow the possibility of any entering the engine.

Do I need to add sealant or a gasket, or, can I just run it with metal against metal?

Thanks
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Old 10-13-2019, 02:11 PM
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Run it metal to metal or use a thin film of RTV (sensor safe!!) between the engine and muffler. I use RTV all the time. Never a worry if a little oozes in. Just make sure the rtv cures before running the engine. Otherwise it might blow out and leak.
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Old 10-13-2019, 02:14 PM
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Thank you 1QwkSport2.5r.
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Old 10-13-2019, 09:53 PM
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Oh, and DONT use paper Gaskets!! you most certainly will have either a loose muffler, or NO muffler upon landing.
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Old 10-14-2019, 04:50 AM
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The reason they talk about sealant is that if any gets sucked back in to the cylinder during the intake stroke it will snuff out the plug.

You don't need a gasket or sealant if the faces are flat.
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Old 10-14-2019, 09:57 PM
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Originally Posted by BarracudaHockey View Post
The reason they talk about sealant is that if any gets sucked back in to the cylinder during the intake stroke it will snuff out the plug.

You don't need a gasket or sealant if the faces are flat.
That’s an old wives tale AFAIC. I cannot say I’ve ever had RTV snuff a plug out - I even tried to force it to happen. The engine just blew the bits of silicone out the exhaust. (I stuck a dozen chunks of dried RTV down the carb with the engine running both at full honk and at part throttle).

I’ll tell you, even the highest quality engines leak between the exhaust port and muffler. I would always recommend a thin layer of RTV on the muffler. It’s not rocket science and it does make a significant difference most often. YMMV, but probably not by much.
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Old 10-15-2019, 11:44 AM
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I use a thin film of epoxy.
No leaks. and easy to get apart if necessary.
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Old 10-15-2019, 09:15 PM
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Originally Posted by Stoneweapon View Post
I use a thin film of epoxy.
No leaks. and easy to get apart if necessary.
I’d not want to use epoxy. RTV is way easier and cleaner, and bare metal to metal easier yet. But I guess if it makes you happy.
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Old 10-16-2019, 04:36 AM
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Heli guys have been using epoxy on mufflers for years when the surfaces aren't perfectly mated.
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Old 10-17-2019, 07:11 AM
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I take a fine single cut file and take a few swipes with my thumb pushing in the centre so there is no rocking, and it just takes the top of the machining marks off. I don't use a gasket. I had to LOL at Qcksport pouring silicone down the venturi. I don't mind a 'little' mess but have not noticed any. I have a few swap meet engines with some silicone stains that don't like to completely come off. Sparingly I guess.
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Old 10-19-2019, 07:43 AM
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Originally Posted by aspeed View Post
I take a fine single cut file and take a few swipes with my thumb pushing in the centre so there is no rocking, and it just takes the top of the machining marks off. I don't use a gasket. I had to LOL at Qcksport pouring silicone down the venturi. I don't mind a 'little' mess but have not noticed any. I have a few swap meet engines with some silicone stains that don't like to completely come off. Sparingly I guess.
I tested the myth of silicone killing a plug by taking dried rubbery chunks and dropped them down the carb. Some bits took longer to blow out. I wouldn’t expect any device to function well if it ingests wet silicone.
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