650r valve recession ??

3 replies to this topic
  • woodsryder

Posted October 31, 2005 - 04:15 PM


After suffering through the infamous 2002 CRF valve problems, I over reacted and bought a 650r. I heard stories of 10-15,000 mile engine life on these things when my CRF needed to be freshened up after 2-3 thousand miles.

Maybe I'm cursed but I only got about 1800 miles on the 650 before one exhaust valve started tightening up fast. I normaly check valves every 300-400 miles, but started doing longer adventure rides (800-1000 off road miles) I'm an ex honda dealer mechanic with a long history of building engines and racing. I am a fanatic about maintenance, I always have a clean filter, and never hit the rev limiter. In short,.. I just don't deserve this! :banghead:

Enough whining, here's what's happening. Valves were rock solid and hardly ever changed for the first 1800 miles and 4 valve checks. I went on a week long 1000 mile ride, and both intakes loosened .001, the left exhaust tightened .001 and the right exhaust tightened up .007!! (from .009 to .002) Well maybe it was a fluke, and at least it wasn't zero. Yes the crank was positioned right, and I checked them cold.

I set everything back to specs with the exhausts at the wide end .009. After an 850 mile rocky mountain adventure I checked them again. Same story only worse. This time three valves hardly moved but the right exhaust was WAY tight. I'm talking two full turns of the adjuster just to get any clearance. :banghead: Surprisingly, it still ran and started OK??

The problem valve is on the right, so it can't be related to the decompressor. I occasionaly use a lead replacement additive to help cushion the valves. The right threaded adjuster is visibly farther out than the left one,.. like maybe .060-.080, which tells me there may have been a problem from the beginning since I only backed it out 2-3 turns in an attempt to restore clearance?

I only have 3600 miles now. Anyone else have valve recession problems or heard of any service bulletins?? I still have the Neway valve cutter set from the 450 fiasco, any chance the seat angles are the same?

  • captb

Posted October 31, 2005 - 04:58 PM


Mine hasn't needed more than .001 adj. in 5K miles, uncorked, pipe, jetted runs cool and it's geared tall, is there any play in the rocker arm? It sounds like a problem from day one, maybe the seat wasn't completely seated in the head and was machined now it's seating deeper when it gets hot.

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  • Old_Man_Time

Posted October 31, 2005 - 06:47 PM


This may be hard to swallow but most likely your decompresser engaged before you made the adjustment. This is very hard for tuners to get used to on these XR650R's.

When you are lining up Top dead center on the compression stroke if you let the motor rotate backwards even a hair it will engage the decompresser. The valves will be way out of adjustment as you have indicated.

I have got into the habit of pulling my flywheel cover and being extremely careful not to let the engine back up when I'm lining up the mark. If the engine moves backwards even a little you need to go 3 full turns before lining up the marks again. Make sure you are rotating the motor in the right direction before you attempt to line up the marks or you will always have the auto decompresser engaged.

I'm really surprised you did not have a lot of valve clatter.

  • woodsryder

Posted October 31, 2005 - 08:26 PM


Thanks Old Man Time, I figured it out soon after posting, and you were pretty much on the money. This time it did clatter loudly and made me do some research.

I'm feeling a lot happier if not a little embarassed. I jumped to a bad conclusion because of valve experiences with the CRF and I assumed only the left exh was actuated by the decompressor because the lever is over there. It turns out the 650 has a lot more sophisticate decompressor than the CRF and others I worked on as a mechanic till the early 80's

There are actually three ways to reduce compression. The handlebar lever presses down on the left exhaust as I assumed. The right valve can be depressed two ways, there is a decompressor cam that eases the force required when kicking, and there is a reverse decompressor cam that works only when the engine rotates backwards (backfires). So there's a manual lever on the left valve to help you get past TDC, and two diffrent cams that can actuate the right valve when kickstarting, and when the engine backfires. Wow,.. it takes a lot to tame this beast.

Here's a link to read more about it. This describes an 86 XR600R but should be the same as the 650? http://www.xr650r.us/tech/decomp.pdf

The last time I got a small amount of reduced valve clearance, it was just probably seating in. This time it was a massive amount due to one of those cams being partly activated and I assumed the worst. The tip off was that it DID clatter loudly this time indicating I inadvertantly put too much clearance back in. The flywheel must have rotated back? I tried to simulate it and can see that the reverse decompressor cam engages immediately at the slightest backward motion.

The moral of this story,..watch that flywheel, and think before you post!

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