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XR400, one valve out of whack after rebuild

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hey, i searched TT long enough, many people have similar problem but it isn't hitting the spot.

I just put new cam chain and rings in my xr. Everything is back together. tried kick starting it and got nothing. So me and my friend adjusted the valves, and we noticed that 3 of them were good. But one valve (decompressing valve/front right valve) was sticking. when we aligned the piston TDC, it would stick and couldnt move it what so ever. and then we would do another rotation and put it to TDC and then it was too loose. We think this has something to do with the self decompression thing on the camshaft. Do you have to position the decompression switch on the camshaft a certain way?

Need help please

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hey, i searched TT long enough, many people have similar problem but it isn't hitting the spot.

I just put new cam chain and rings in my xr. Everything is back together. tried kick starting it and got nothing. So me and my friend adjusted the valves, and we noticed that 3 of them were good. But one valve (decompressing valve/front right valve) was sticking. when we aligned the piston TDC, it would stick and couldnt move it what so ever. and then we would do another rotation and put it to TDC and then it was too loose. We think this has something to do with the self decompression thing on the camshaft. Do you have to position the decompression switch on the camshaft a certain way?

Need help please

You need to rotate the crankshaft counterclockwise only to disengage the auto-decompressor.

Do you have a service manual? If you don't have a shop manual, download it in .pdf format here.

http://www.sendspace.com/file/ivcn6l

Perc

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+1 You must only rotate the crank CCW when setting to TDC and it must be at TDC on the "compression" stroke. You can distinguish the compression stroke from the exhaust stroke by feeling for wiggle in the sub rocker arms at TDC. If you can feel some wiggle, you're on the compression stroke.

You need to make sure when you adjusted the other 3 valves you were on the compression stoke, if not, then they are set wrong and you need to redo them.

You need to rotate the crankshaft counterclockwise only to disengage the auto-decompressor.

Do you have a service manual? If you don't have a shop manual, download it in .pdf format here.

http://www.sendspace.com/file/ivcn6l

Perc

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is it seriously that simple??

My friend adjusts valves all the time. why is this so much different for him? or is it this way only after a rebuild?

and on the exhaust stroke is when the one valve sticks.. and the other valve is fine with a tiny bit a play in it.

-so adjust the one (sticking valve) when on the compression stroke(when its "too loose") and then everything should be fine and my bike should be able to start?!?

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oh and btw.. after assembling my engine i found a tiny spring... it supposed to be under the "plunger"... what is going to do not being in the engine?

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oh and btw.. after assembling my engine i found a tiny spring... it supposed to be under the "plunger"... what is going to do not being in the engine?

Oh well... let me think. :banana::thinking::lol:

I'm pretty sure you need that spring for the auto-decompressor to work. Sounds like your decompressor may be malfunctioning until all the parts are back.

Did you have the service manual?

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I had similar problem after rebuild. Decompression valve used to stick every 2nd cycle, because plunger was sticking. I’m sure that if you take your head cover, remove camshaft and carefully clean hole where plunger and spring sits it should be ok. When everything is like it should be , plunger should freely move down then you press it with finger and go up/return then u release it. If it won't then clean it again until it does. And don't forget to re-check valves after doing this. Good luck

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The spring and plunger must be installed for the cam mounted auto decompressor (which operates the RH exhaust valve) to operate properly. The auto decomp must be disengaged when setting the valves. Rotate the engine slowly CCW until you hear a "click" from the top of the engine, this is the auto decomp releasing. At the same time you are rotating the engine, watch the intake valves, when they close, the piston is coming up on the compression stroke. Line up the "T" timing mark on the flywheel with the notch in the cover and adjust the valves. If the RH exhaust valve is being held slightly open by the auto decomp, rotate the engine CCW again for two revolutions and check. Sometimes it will take 2-3 tries before the auto decomp is released.

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I agree with these guys. You're going to have to take the head cover off again and install that spring. And then check/set/reset ALL valve clearances, not just the right exhaust.

And it's a good thing you mentioned this boo boo. We could have been chasing this problem for a long time.

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haha, yes indeed! thank you guys for your help! you guys make my life easier :banana:

the problem is fixed. my bike is running at its best!

I'm happy. the bike is loud. and my neighbors are aggravated, life is back to normal :lol:

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haha, yes indeed! thank you guys for your help! you guys make my life easier :banana:

the problem is fixed. my bike is running at its best!

I'm happy. the bike is loud. and my neighbors are aggravated, life is back to normal :banana:

Wow! I'm impressed! :lol: You just jumped back in there and fixed it. Good for you! :banana:

Most folks seem to talk about these problems a little more. I guess, just hoping they go away on their own. Glad to hear the neighbors noticed. :banana:

Perc

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