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Top end rebuild problems

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I have an xr 70 that was tired.... would idle but no power. Tore it down and the rings wore so worn. I bought a top end rebuild kit off eBay for $90 that came with new head, cylinder, pistons etc. I watched a bunch of videos and consider myself pretty handy in the shop. 

I installed the new parts, timed it with the 0 on the notch at TDC when the valves were closed.... tapped the valve clearance at .002 and everything appeared to be perfect. I didn't follow the book and I tightened the head bolts probably too tight (I now know they should only be 8 ft lbs.) 

I kicked it over a few times, sounded good and then then on the 2rd or 3rd time it felt weird... then tried to push start it and still wouldn't start. Took stator cover off and piston sounded like it was scratching a little on the down stroke when I turn the flywheel by hand....

Took the timing cover off and now it's like 75-90° off and the 0 is no longer on the notch at TDC. So I took it apart and looks like the intake valve now doesn't close all the way and I can get my .002 feeler gauge in between the valve and seat...

Does anyone know what could have happened? I assume the timing chain slipped, and the piston hit the valve since maybe the head bolts were too tight?

Thanks for any advice. I ordered a new valve, the piston and rings and cylinder still look good.... 

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The head bolt torque didn't cause it.

When you double checked it are you sure you were on the correct TDC? The crank does make 2 rotations for ever one rotation of the cam. Just getting that out of the way.

Is the sprocket still tight on the cam? Did you put the cam chain tensioner plunger and spring back in correctly?

TBolt sells good aftermarket big bore kits and heads for a reasonable price. I have had experience with them and they hold up. A 88cc cylinder and piston kit is around 120. A "racehead" is around 250. With the head you get a fully built head, cam, piston and gasket kit.

With a $90 eBay kit, you may have done everything 100% correct, but the parts were junk from the start.

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With a $90 eBay kit, you may have done everything 100% correct, but the parts were junk from the start.

That was my thought too

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Yeah, I think you are right. After further inspection it looks like the valve  didn't touch as there are no marks on it or the piston. If I tap on the valve it goes all the way in... if I push on the spring to open the valve, it opens and then doesnt close all the way and can get a .002 feeler gauge between the valve and the seat. Either the valve is bent or something wrong in the valve guide. I drilled out the broken exhaust studs on the old head, tapped them and going to put that one back on with the new cylinder and piston.... wish me luck. Thanks

Edited by Bgeorgal

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