Carburetor intake insulator and o-ring damage

moondoggers · Post by **moondoggers** » Wed Apr 09, 2014 10:29 pm

I stand corrected so maybe to save my self, it could the method of tightening that causes the failure.

Snakeoil · Post by **Snakeoil** » Thu Apr 10, 2014 7:32 am

Doubtful. At first I thought it might be the use of fractional sized O-rings versus metric. But as you should have noticed in my previous posting a 3/32" cross section o-ring is smaller than the 2.5mm ring that would normally go into this application. So the compression and hence stress on the spacer is reduced.

I'm pretty sure is what we see here is simple aging of the insulator material, which I believe is Bakelite or a derivative. Couple that with heat and that is all I think you need for a failure.

If I can lay my hands on a piece of 3/8" Delrin or similar modern plastic, I'll make a couple new insulators and go back to the o-ring design because I think is provides a much more reliable seal. Textolite or Garolite are other materials I might try. I say might because if this gasket arrangement works as it should, I may not need to do this.

regards,
Rob

malcolmgb · Post by **malcolmgb** » Thu Apr 10, 2014 11:53 am

I have some resin laminated material but it is 1/4" thick approx 2" wide, I am in the US in 3 weeks and would be happy to send you some to try, send me a pm with your details.

Snakeoil · Post by **Snakeoil** » Thu Apr 10, 2014 4:20 pm

Thankjs for the offer, Malcolm. But I'll be able to find the stuff. I can order it from at least two industrial supply houses not to mention probably being able to mooch some from my buddy who still is still working for the company.

That was a very generous of you to offer.

regards,
Rob

Snakeoil · Post by **Snakeoil** » Fri Apr 11, 2014 6:09 pm

My used spacers from ebay arrived today. They still had the O-rings in them and they were so dry that they are more like plastic than Viton or nitrile. They look smaller than 2.5mm to me. But they are flattened out and my guess is these were the ones that left the factory in the bike.

I'll measure them tomorrow and see if I cannot boil them or do something to get them to take back their original shape so I can measure them more accurately.

Insulators are perfect so I now have 3 spares if I ever go back to the original design.

regards,
Rob

garncarz · Post by **garncarz** » Tue May 13, 2014 8:21 am

FWIW, I have used 1/2" baltic birch plywood with a rustoleum high heat engine paint coating to make carb spacers. Easy to machine, cheap, excellent insulator, works like a charm.

Snakeoil · Post by **Snakeoil** » Tue May 13, 2014 7:03 pm

Funny you should mention that I considered making some from rock maple. Good input. Maybe next time.

Regards,
Rob

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Carburetor intake insulator and o-ring damage