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rfx125

Why me?

9 posts in this topic

Who can tell me why my new complete GYTR ported head assembly has leaky valves (I & E leak down is excessive)?

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Has the head been run? What method are you using to test how well the valves are sealing?

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I'd be pissed too. A $1500 head should not have leaking valves. Are you testing them on the bike with a leakdown tester, or off the bike with solvent?

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Leakdown @ TDC with the cams in, leakdown @ TDC with the cams out, leakdown @ BDC with the cams out; all well over 15% leakdown. Valve clearance wasn't what I was expecting from GYT, either, intake clearances are out of spec, exhaust are in the middle.

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Leakdown @ TDC with the cams in, leakdown @ TDC with the cams out, leakdown @ BDC with the cams out; all well over 15% leakdown. Valve clearance wasn't what I was expecting from GYT, either, intake clearances are out of spec, exhaust are in the middle.
KJ asked "has it been run?", and you gave no answer. It's a pertinent question. Smart builders will never lap titanium valves, and in the case of the GYT-R head, which, like it or not, is a production assembly rather than custom work, it's likely that the head started and finished with new valves and a head off the shelf, making the matter of sealing just about exactly like a brand new bike.

Run the engine for an hour and test it again. There should be a significant difference.

Valve clearance cannot be accurately set on the bench each and every time it's done. With a seasoned casting, it's a bit more likely, but the clearance can only be accurately done with the head torqued in place. It doesn't really surprise me that they'd be off a little.

Leak down testers are not made to a particular standard like a pressure gauge would be. 3 different testers will usually yield 3 different results, and it's only useful if used repeatedly on the same engine, or on several engines of the same type, so that some meaningful comparison can be done.

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Yup, like Gray said, I've seen many freshly assembled heads leak before they are run. Once they are run for a few minutes they tend to seal up. If it is still leaking after you have run the engine for a little bit then there is something wrong.

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I like to use a black marker to check the valve seat contact area in relashion to the valve face. This way doesnt affect the machined surface or valve. Color the seat/valve face and lap by hand by slowly turning with medium pressure.

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Yup, like Gray said, I've seen many freshly assembled heads leak before they are run. Once they are run for a few minutes they tend to seal up. If it is still leaking after you have run the engine for a little bit then there is something wrong.

Very true... they will pound thier own seat and seal lol.

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