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Engine basics => Engine set up tips => Topic started by: Paul Allen on April 16, 2022, 03:13:00 PM
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Has anyone had the venturi O ring expand enough so it no longer seals. I had this happen on a PA 51.
Thanks.
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Has anyone had the venturi O ring expand enough so it no longer seals. I had this happen on a PA 51.
Thanks.
Yes. Some of the o-rings had a larger cross-section, so when you went to compress them, they "squirted" out the side, and wouldn't seal. Some of the venturis have an undercut to give it a bit more room. I don't have any PAs any more, but I just got the recommended o-ring for the dimensions from McMaster. I want to say the cross section was 1/16th, but this was about 20 years ago, so don't be too surprised if its wrong.
Brett
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Thanks Brett.
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Go Down to your local auto parts store and see what they have. That is where I got some for a couple of engines I have. D>K
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Thanks John, I think what Brett said about under cut the shoulder is a good idea, at present it has a very small shoulder.
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Get a variety of different fits and sizes to have on hand to use on your different engines. The different varieties of rubber have different durometers and some compress easier than others. If any doubt about fit or in an emergency case just wipe a small bit of silicone around the ring to take up any gaps. I have made paper gaskets before to slip onto the venturi first before the o-ring to help take up some slop if I think it needs it. Viton and the red silicone high temp rings are the best I think if you have a source locally for them that you can go to in order to test fit them.
Type at you later,
Dan McEntee
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Thanks John, I think what Brett said about under cut the shoulder is a good idea, at present it has a very small shoulder.
That's an alternate way to deal with an o-ring that is too small. The original black ones that were supplied with the engine worked fine as they are. The later silicone (red) ones sometimes have the problem you describe, with some venturis. Simpler solution, not requiring a lathe, is to get the size with the right cross-section. Unfortunately I do not have the dimensions - I want to say 1/16 but I would get one size larger, too, and see. Fortunately they are cheap.
Brett