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Valves, Shims, Seats

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I recently had a lot go wrong on my bike... Steering bearings, TPS, Cam chain stretched. I know that at least two of these things are just wear and tear work. TPS was a bother though... not hard to do just frustrating to have it happen. BTW.. when changing the cam chain I did the piston. So did all this work and still nothing... now in my defence I checked the valves at one point but it was when the cam chain was stretched... rechecked using the bikemaster feeler gauges (tapered style which really helps on the center intake).. All the intakes were tight... really tight...

I've reshimmed and it now starts with two kicks... so that's awesome but I really can't wrap my head around the reason that the valves get tight.

I mean the valves are titanium right?? how do they wear. I read in a post that you should only reshim 2x then get some work done. I know the seats were mentioned.. I'm wondering if anyone has pics of what needs to be done??? I'm gonna start saving for new valves/seats etc.. but I think I should be good until at least next season...

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The valves stretch over time, the seats wear down, and the valve face wears down over time too. As this happens the valve stem tip get closer to the cams causing a tight condition, which means you have to go to a smaller shim to get the gap correct again. Let em wear and stretch too much will cause a valve to break and this will take out other parts with it.

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Not sure about stretch but wear down the valves definitely do. The valves hit the seats thousands of times as the engine runs. All that banging against each other cause wear on the valves and the seats so the valves will "seat" further into the seats/head, at the other end of the valves are their stems that push against the shims, the buckets, and finally the cams. As you can see, when the valves and seats wear down, the stems will protrude a little further out the other side where the cams are, this causes the clearances to be smaller hence you'll need smaller pads/shims to adjust the clearances.

The titanium valves have a coating on them that once worn out they will wear faster, that's why after a couple of adjustments and the coating is gone, they will wear much faster. This is why you need to rebuild after the coating wears off - typically after 2 adjustments.

On rebuild, re-cutting the seats by a reputable company allows the new valves to seal and seat better.

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OK.. that makes sense so far. Thanks to you both!! av.. you say re-cutting the seats... another question comes from this. according to the exploded yamaha fiche the seats are on the valve shaft (intakes Ref #4 and the exhaust are Ref#5 on THIS site)

I thought seats were on the head and the valves "sat" in them???

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The seats are pressed into the head. I don't see them in any parts explosions, so I assume yamaha does not sell seats separately. The seat is what the valve face rests against, it deforms with the valve, so when you get new valves, the seats need to be re-machined to fit the new valves.

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I thought seats were on the head and the valves "sat" in them???

you are correct. I don't know what the site you looked at is talking about.

The biggest factor in valves changing is dirt or grit on the seat causing premature wear. combining grit and max rpm's and you've got a formula for quick wear.

A good clean air filter and good filter oil are a necessity.

FYI, on my last 3 250f's, I've had to shim 1 time and that was at the 60 hr mark. I ride in the upper rpm's on an mx track mostly. The shimming happened not many rides after I misinstalled my air filter allowing unfiltered air into motor.

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I recently had a lot go wrong on my bike... Steering bearings, TPS, Cam chain stretched. I know that at least two of these things are just wear and tear work. TPS was a bother though... not hard to do just frustrating to have it happen. BTW.. when changing the cam chain I did the piston. So did all this work and still nothing... now in my defence I checked the valves at one point but it was when the cam chain was stretched... rechecked using the bikemaster feeler gauges (tapered style which really helps on the center intake).. All the intakes were tight... really tight...

I've reshimmed and it now starts with two kicks... so that's awesome but I really can't wrap my head around the reason that the valves get tight.

I mean the valves are titanium right?? how do they wear. I read in a post that you should only reshim 2x then get some work done. I know the seats were mentioned.. I'm wondering if anyone has pics of what needs to be done??? I'm gonna start saving for new valves/seats etc.. but I think I should be good until at least next season...

Talk to Jesse (Williamsmotowerx) here on TT. He is a TT sponsor and has a lot of knowledge with this subject. Also if you need the head rebuilt he's not that far from you being just in Wisconsin. He does excellent work and for what you get from him the price is pretty sweet too. Depending on where you live in Ontario. I grew up just outside of Sault Ste Marie MI on the Canadian border. :)

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Guys thanks a lot for all the input. I don't think I need to get the work done yet but I'm the kinda guy that needs to know why.. not just let someone else do the work for me. that being said I've heard many a good thing about Williamsmotowerx and I realize that somethings need to be left to the professionals! I'll be msg'n him b4 the end of the season for sure!

btw charlie.. I'm over in the niagara falls side of Ontario...

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