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Valve sealing? Valve sealing?
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 25 Oct 2009
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Valve sealing?
I've got the cylinder head off on the bench (see previous thead). I've checked the valve seating by pouring petrol in through the ports to see if it leaks through. It does, but only a small amount. If you pour the petrol in, after about 5 seconds there is a slight wettening of the edge of the valve as seen from the combustion chamber side.

I'm sure it ought to be 100% fuel-tight, but this seems reasonable, or does it? I don't want to regrind the valves unless I have to, but now would be a good time if it was necessary.

Any thoughts or comments welcome.
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Old 25 Oct 2009
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I've heard that 10 secs is a benchmark - but its a bit of an approximation - need to do a "leakdown" test - but thats before the head comes off

As you've got the head off - best just to give the valves a mild "lapping-in".
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Old 25 Oct 2009
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Thanks for the instant reply! Hmmm - thought it might mean more work. I'll give the valves a quick lapping, then. As the postal strike means I'm not going to get the new headers any time soon, I might a well make full use of having the head off.

Cheers.

Now, where did I put that grinding paste ...
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Old 25 Oct 2009
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Do yourself a fovour ad do the valves now that the engine is opened.

Its really easy and you can make them sealing perfectly with a few minues effort.

Mount the end of the valve in a drillmachine, and put some mild grinting/valv-paste on the valve. Then spin the valve around in its bowl with the drilmachine (cant remember the english name, but the electrik drill, thingy =))

A couple of seconds and youre done, and a lot happier
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Old 26 Oct 2009
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Thanks Jens. I've ground in plenty of valves over the years! I tend to do it by hand. I find using a drill too harsh unless the valves/seats are very bad.
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Old 26 Oct 2009
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BDZ, I agree - by hand is best - probably a few minutes each valve should be plenty!
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Old 27 Oct 2009
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With the electric drill you get a much more even pattern, by hand you risk making it a bit oval.

But do what you find best, and good luck
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Old 27 Oct 2009
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Check that lapping in valves is okay for this model, on some modern bikes (not sure if the XT qualifies...), it's not recommended i.e. DRZ400.
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