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2003 XR50R won't start

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2003 XR50R with big bore kit, strong spark, good compression, new carb, new cdi, key switch and stop button bypassed (open circuit) and bike won't start.  360 ohms on stator and 120 ohms on pulse generator.  I'll be checking the timing and valve clearance tomorrow.  Apparently it was running fine, bogged out, died, and never started again.  I've heard the woodruff key can shear off and through off the timing.  Any other ideas?

Edited by mossman77

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Also, stock valve lash is 0.002" IN/EX.  Should it be a bit more considering the big bore kit?

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Found the issue...the exhaust valve locknut is missing.  Apparently it backed itself off.  The exhaust rocker just flaps around for the majority of the stroke.  So I'll be putting on a new nut and hopefully that will resolve things. 

On a different note, I believe the timing may be 180 degrees off.  Except it was running fine for a year.  Is it even possible for an engine to run with the timing 180 degrees out?  Valves are closed with flywheel at T marking and circle on cam gear 180 opposite the notch on the case.

Edited by mossman77

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Forget the question about 180 degrees out.  I realize that isn't technically possible since the plug fires on twice per cycle.  However, the cam gear was put in 180 degrees off from what it is supposed to be.  Anyway...I pulled the head and don't see the nut anywhere.  It must have fallen through the oil passage, which is conveniently located just below the exhaust rocker :foul:.  I drained the oil and it didn't come out.  I suppose I should pull the covers and continue searching for it?  I don't really feel comfortable leaving it rattling around inside the case, for obvious reasons.  That oil passage is on the left side of the case.  Any clue where it likely ended up?  Maybe sitting on the oil strainer screen?

Edited by mossman77

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This is the passage where I believe the nut fell through (red arrow) and where it may have ended up (blue arrow).  Perhaps I could overfill the crankcase then stand the bike up and get the nut to fall into the rear of the case so it would come out of the drain plug hole.:rolleyes:

 

 

 

 

CrankcaseHalf_XR50R.jpg

CrankcaseLeft_XR50R.jpg

Edited by mossman77

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I would drain the engine oil and then tilt the bike on a 45° angle to the left, remove the right side engine cover, and use a telescoping magnet to search for the tappet nut. There are a few open holes along the bottom of the center case where you can stick the magnet through to the other side, you'll just have to work at it. In the event you still can't find it, you should pull the engine and split the cases, that metal nut will play havoc with those metal trans gears real quick, for starters.

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It looks like the drain plug is directly below and to the right of that passage, so it seems like it should've come out when I tilted it.  I'll try what you said and worst case split the cases. 

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I'd just leave it. Should be fine. The nut is to big to get between the gears.

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I find that hard to believe, unless the gears are the size of those inside a wristwatch.   It could get stuck many other places and have catastrophic consequences.   For instance, between a gear and the case, or between. The clutch and the case, etc.

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is it possible that to oil got drained at one time and the nut is long gone? what about a magnetic drain plug bolt? it would sure be nice to find that nut stuck to the end of the drain bolt

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Didn't even think of that.  I'll ask the owner when he last changed the oil.  I was thinking a magnetic drain bolt would be a good idea.

Edited by mossman77

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