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dewercs

Thanks to Grayracer513!!!!!!!!!!

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I just want to say thanks to grayracer513, he saved me alot of money!!

I'm currently a career Medic/Firefighter and a former Aircraft mechanic (mostly small piston aircraft) i have worked on 2 and 4 stroke engines for the last fifteen years. I currently race a 2004 yz250f and a 2007 yz450f, I am getting ready to put a high comp. piston in the 250f, I have not taken down a modern 4 stroke mx bike yet, I did do the cam mod on a yfz450 quad with no problem, which was really easy. Anyway the most of the time when you take a cylinder off a aircraft engine you lapp the vavles, which are not titanium, so thank god i read his and others advice about not lapping tit. valves!!!! Also is there anything else not to do, or to look for when i replace the piston and rings, I will be replacing the timing chain and useing assembly lube. Thanks in advance!!!

Charlie

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Just curious to know what lapping valves are.. My best advice to you is to get a manual and read it before starting. It will tell you what you need to do or lack of.

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Just curious to know what lapping valves are..
Lapping valves (or any other two parts that fit together) is a means of doing a light refinish on the parts involved, and of matching them together.

It is done by applying an abrasive paste to the joint between the parts and working them back and forth over each other. In the case of valves, the past eis applied to the valve face, and the valve is spun back and forth in its seat. This grinds one face against the other so that competing high spots wear down evenly with the opposite face, and they match up.

The problem with doing this to titanium valves is that Ti valves are coated with various ultra-hard compounds, often titanium nitride or a variant. This is necessary because titanium is not hard enough to be used as a valve face, and there is no suitable way to harden it for this application. The nitride coatings are extremely thin (less than .0004"), and the loss of any of the coating by lapping the valves would shorten the life of the valve.

If the valve seats are properly refinished when the valves are replaced, Lapping is unnecessary, in any case.

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Thats pretty interesting. I can see how it might help to seal things up. I always just filled the head with water to see if any of the valves were leaking after a rebuild. I imagine that paste could also widen clearances that you dont want to. Would you attach a dril to the end of the valve to sand them? Or just turn them by hand? That seems lengthy, haha.

Thanks for the info Gray :applause:

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It's done by hand with suction cup on a round wood handle spun between the palms. But again, never on a Ti valve.

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