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Makotosun

Leak down test

  • tlh0824
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Leak down test was created by tlh0824

What's a good or passable leak test. After 3 minutes I dropped from 6lbs to 5lbs. I have a small leak where the manifold touches the reed. I put a thin layer of ultra copper, but it didn't help. Is that as good as it gets? Any other ideas?
Thank you,
Tom
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28 Nov 2020 10:56 #1

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Replied by turbodan on topic Leak down test

1 psi in three minutes is not bad but if you know there is leakage in that area it would be worth taking steps to resolve it.

I would cut a .030" or .040" paper gasket for the joint and apply something like Hondabond HT to both sides. The old rubber manifolds often need help sealing up. The molded on sealing lips have long since gone flat.
28 Nov 2020 19:26 #2

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Replied by MarkT on topic Leak down test

Zero leakage is attainable.

Ultra Copper is not a good choice, does not hold up to fuel. Semi-hardening Yamabond works well on manifolds... same stuff used to seal case halves.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
28 Nov 2020 19:34 #3

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Replied by tlh0824 on topic Leak down test

I put a little ultra copper at the cylinder base gasket, as that was leaking a little bit too. It took care of leak, is that ok to leave?
29 Nov 2020 11:40 #4

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Replied by MarkT on topic Leak down test

It shouldn't hurt anything... but might start leaking again.

I'm also getting the impression you might be adding some sealer over the leak area? What needs to be done is disassembly and thin coat of yamabond or hondabond or permatex motoseal or threebond (all pretty much the same stuff) semi-hardening on new (or at least undamaged) gaskets.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
29 Nov 2020 11:54 #5

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Replied by tlh0824 on topic Leak down test

No, I put a thin coat on the gasket, both sides, I have yamabond, it just didn't occur to me to use that.

I just cleaned up the manifold and applied yamabond, fingers crossed- I will give it 24 hours before I re-test.
29 Nov 2020 14:02 #6

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