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Old 03-28-2012, 01:35 PM   #1
worldrider555 OP
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Location: Quakertown, PA
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Xr650R motor troubles- Smoking bad

Hello, I have searched a good bit an haven't been able to really hit on what my problem is.

I have a 2000 xr650r that was supposed to have had a recent ring/hone and valve seal job.

It ran great for awhile but it recently has began smoking a good bit.

I have checked valve lash and that seems to be good, but I ran a compression test and that seems to be way low. Could only get the compression up to around 90 at the most.

So i built a leak down tester and put 100psi to the cylinder while holding it at TDC. I could hear the air coming out of the airbox (the crankase vent had been disconnected.

This signals some kind of problem with the intake valves correct?

Can any more tests be run of should I just open up the top end?

Thanks for all the help.
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Old 03-28-2012, 01:56 PM   #2
Joined: Feb 2010
Location: Sydney
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Sems as though you are describing two separate problems. One is compression and the other is smoke.

If the top end was recently done, your leak down should be stronger. Make sure you are at the correct stroke with TDC. You can do this by feeling for lash on both tappets. This will indicate valves are seated.

One trick then is during leak down tap a valve to dislodge any possible obstruction. I have known this to work and pick up the value immediately.

As for smoke, I recently found my valve guide to be drilled off-centre by 0.5mm. I purchased the bike after a two attempts by the shop to fix a smoking issue and $3500 spent by the previous owner but the smoke was still there.

What the offset guide does is stretch the seal and allow oil to seep down the valve stem. High compression motors hate this.

For the record, the shop in question is known here in Australia as the XR650r GURU and was renowned for building the Safari winners. They know jack about heads though as they even seated the valve in an offset position.

Even on purchasing new valve guides some were rejected as they too were offset.

Good luck.
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Old 03-28-2012, 02:09 PM   #3
worldrider555 OP
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I made sure I was holding it a TDC, I had the marks aligned and checked for play.

As far as compression I'm not positive that the gauge was working right, maybe that could be because of the auto decomp in the cam?
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Old 03-28-2012, 03:39 PM   #4
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If you think the auto decomp is screwing with the leak down test back the adjuster nuts off on the exhaust valves.Finding a reliable machine shop the has good quality control can be tough.Its amazing how well the japanese can assemble an engine-and 1 redneck can screw it up.I did a new top end on my xrr and replaced the valves only and machined the seats-the valve guides were good .At least you can pull the top end without pulling the whole engine.when i did my top end I had the cylinder rechromed and ran a new honda piston and rings.
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Old 03-28-2012, 04:07 PM   #5
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Ill try that tip with the valves.

Im thinking about sending it out to XR's only. Seems if anyone could do it right they could, unless anyone knows a better shop.
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Old 03-28-2012, 04:13 PM   #6
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I assume the cam marks were aligned where they should be, when you lined up the flywheel marks. You said you checked valve clearance.

It is hard to get accurate readings, but if you have air leaking through the carb into the air box, that indicates to me burnt or bent intake valve.

Since your valve adjustment is in spec, my money is on burnt.
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Old 03-28-2012, 04:18 PM   #7
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Location: Fleischmanns NY
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Blais Racing Services

Theres no one better for your XR needs. He is a legendary Baja desert racer, Dakar Podium finisher. Chris Blais.
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