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BENT VALVES ON 2003 XR 80

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MY DAUGHTER RIDES A 2003 XR 80,WE HAVE OUR OWN TRACK AT OUR HOUSE. SHE HAS ABOUT 10 RIDE SESSIONS UNDER BELT. WE ARE ON OUR 2ND ISSUE WITH BENT VALVES, THIS HAPPENS WHEN BIKE IS HOT AND TURNED OFF, WHEN STARTING YOU HEAR THE CLACKITY SOUND AND OF COURSE IT WONT START BACK UP. MY DEALER SAYS OVER REVING,I AM WITH HER WHEN THIS HAPPENS. I HAVE NEVER HEARD TO ENGINE REVING TO THE POINT WERE I WOULD SAY UP SHIFT. I DONT UNDER STAND WHAT COULD BE HAPPENING IF OVER REVING WAS THE CAUSE WHY DOES IT ONLY SHOW ITS SELF WHEN STRTING THE ENGINE ?? WAITING FOR SOME INPUT FROM YOU GUYS :cry:

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Could be over revved when airborne....hard to say without being there! Could also be improper cam chain length/adjustment, cam-crank timing, gasket thicknesses, etc.

A leaking valve, whether bent or a bad seat, will always show when starting. When running with that problem, there is still enough compression left, even with the leak, for the motor to operate. At start-up, because the engine is turning over much slower, the compression has more time to leak out, so it doesnt run.

Generally speaking, those valves should only bend if there is a component failure, faulty workmanship, or over-revving.

Hard to say what the cause is from here.

Get a manual and do your own work, and triple check everything. XRs are easy to work on.

Robert:cheers:

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Thats a bunch of bull,Unless your daughter is over reving from start to finish of riding session there is a problem.I just bought a used but almost new 03 xr80 and i rev the crap out of it with no problems.It is my sons bike but sometimes daddy takes it out for a spin.These bikes are supposed to be almost bullet proof.Go back to dealer there is something being overlooked.Good luck.

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Your dealer is making excuses. Not helping you with solutions.. and if this is the second time,, and that same dealer did the work,, I'd be seeing the owner,, and in a very stern voice, be "suggesting" my money back,,a new bike, or suggest he get a good lawyer.

My Boy has a 2004 CRF80,, it really can not be revved hard enough to bend the valves,, let alone twice.

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If you daughter can rev it and bend two valves, you need to sign her for some races. It takes a pretty long straight pinned with no sign of letting up to bend a valve. I've logged thousands of hours on these little piles of fun and I've only bent maybe 4 valves. And two of those were oversize valves with cams. The only problem is, if it was put together wrong like perhaps the cam chain being one tooth off, it would run like crap. Off the top of my head I can't think of any other way you could put it together wrong and not know it and bend a valve. The only thing I can think of is to take it apart and check the valve clearances and double check the cam chain being a tooth off. Or maybe the gear on the bottom is off. So when you put it back together everything lines up, but in reality it's off. To check this, pull the flywheel off and the teeth on the lower cam gear should line up with the keyway slot perfectly. If it doesn't, there's the problem. If it does. Then, I don't know. :cry:

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I have a cam in my motor with HD valve springs and an Inner rotor ignition and I rev it untill the valves start to float with out any problems. Well Ok i did bend one valve but these are very extreme conditions.

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That is so wild. I found this through google.

Last week my endurance racing partner who isn't mechanicly

inclined brought over a '99 XR80 from a freind of his.

The story he got is the bike had sat for a year and now won't start. He wheels it into the garage and I can smell that putrid smell of rotten fuel.

Drain and clean the tank, petcock and carb.

Try to start it. It sounds funny kicking it, like a

exhaust leak and it's pretty easy to kick.

Pull plug, no compression.

Pull head, both valves bent. This bike is

like brand new. Bet it doesn't have 10 hour on it.

Put a new pair of valves in. Started right up and

runs fine.

Damn weirdest thing I have ever seen.

?

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My guess is:

Since it was sitting for a year or so, the valves were frozen to the guides, so when he went to start it, it bent them.

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I get it.

When they kicked it over the first time in a year the valves wouldn't return fast enough and the piston touched them.

That makes complete sense.

This motor is BRAND NEW. I mean no carbon

on the head/exhaust.

You can just see on the piston where they touched put it didn't even gouge the piston.

Cool. I have new valves in it and it runs like a champ now.

Thanks!

Emmett.

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My boy has an 03 xr 80 i baught new when he was 8 and learning how to use a clutch. he used to ride first gear till the cows came home and the bike has not had any problems. oh 1 problem the chain came off jammed up in the shift lever and cracked the case. but engine does and always has run great. my crf 450 however has valve problems and is at the shop getting SS valves right now.

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I just bought my daughter an 84 xr 80, it sounds like the same symptoms, too easy to kick , wont start,it sat for 3 years, I cleaned the carb, fluhed the tank, and changed the oil put ,a little marvel mystery lube in the plug hole.when kicked over the plug gets soaked even though it has healthy spark.Is it hard to check the valves? all my expeience have been with 2 strokes.

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I just got my daughter a 84xr 80, its been sitting 3 years, I cleaned the carb, flushed the tank an put marvel mystery oil in the the plug hole. It lacks compression and wont start, the plug gets soaked evn though good spark. is it hard to check the valves? My experience has been all 2 strokes.

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Get a Clymer manual, it should pay for itself the first time you use it!

On a motor that old, the problem is probably simple wear. Bore it 1 size up if the cylinder isnt trashed, more if needed. Lap the valves in for a good seal, check the camchain, cam gears, cam journals and camchain tensioner, should run for another 20 years!

Robert :cry:

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For what it's worth he brought the other XR over last week and it suffered

the exact same problem but only the intake valve.

Motor had less then 5 hours on it, sat for over a year, fuel petcock left on,

no fuel stabilizer in it. everything gunked up. pulled head and replaced

just intake valve, reassymbled, started right up and

runs fine.

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