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Nov 14, 2016, 09:05 PM
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OS 25 rebuild


I am resurrecting an old OS 25 R/C (predecessor of the FP series from the early 70s) for a small project. The backplate paper gasket came off in pieces and the carburetor o-ring is hard and brittle. I know that I can make a backplate gasket from card stock, but where can I find a suitable o-ring (9mm id, 11 mm od, 1,8 mm cross section)? What material should it be to withstand glo fuel? Any suggestions will be welcomed. The OS listing of discontinued engines doesn't even list this one - it is old!

Jeff
President, SPA
N9214G
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Nov 14, 2016, 09:25 PM
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Originally Posted by jfo182
I am resurrecting an old OS 25 R/C (predecessor of the FP series from the early 70s) for a small project. The backplate paper gasket came off in pieces and the carburetor o-ring is hard and brittle. I know that I can make a backplate gasket from card stock, but where can I find a suitable o-ring (9mm id, 11 mm od, 1,8 mm cross section)? What material should it be to withstand glo fuel? Any suggestions will be welcomed. The OS listing of discontinued engines doesn't even list this one - it is old!

Jeff
President, SPA
N9214G
We have an old time Ace Hardware store in our area that has just about every O ring you could imagine.

Mike
Nov 14, 2016, 09:38 PM
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Auto part stores are another good source.
Nov 14, 2016, 09:43 PM
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Is there a particular composition that is needed in order to withstand the methanol and nitro in glo fuel? I know I can no longer use auto fuel in my Cessna as the ethanol attacks the rubber seals in the fuel system. Does anyone know what the o-rings in our R/C engines are made of?

Jeff
President, SPA
N9214G
Nov 14, 2016, 10:07 PM
Registered User
Jeff,
Standard o-ring material, neoprene, buna-n, etc., will be fine. Methanol and ethanol are different beasts! The stuff that most hardware stores has is neoprene.

I had one of those .25s in my first 'pattern' plane, a Andrews Mini-Master!

Regards,
Cliff
Nov 14, 2016, 10:12 PM
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Thanks Cliff! Back in the 70s I had a Trainermaster with an OS 40. Loved that plane. The 25 is destined for a Honker Bipe. A bit of nostalgia there.

Jeff
Nov 15, 2016, 06:48 PM
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Went to Ace today. Looks like a US Standard #11 o-ring is the one that will work. Thanks for the replies.

Jeff
Nov 15, 2016, 07:14 PM
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Quote:
Originally Posted by jfo182
Went to Ace today. Looks like a US Standard #11 o-ring is the one that will work. Thanks for the replies.

Jeff
Ace is the place!

Mike


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