Decompressor Failed! What Next?



1 reply to this topic
  • Big_D

Posted February 14, 2004 - 04:56 PM

#1

Over the last couple months my '01 XR650R has become harder and harder to start. The last ride I finnally had to use the Yamaha pagan starting ritual from the YZ400/426. Well it is on the cold side and I have some free time so I decided to tear the bike down for heavy maintenance and see if I can figure out what is up with the decompressor system.

I have not pulled the cam out, but I have opened up the top end. It seems that the spring under the decomressor cam has failed, I can move the decompressor cam up and down and it stays where I leave it. Checking the Service Honda parts fiche, and with my local dealer the spring is not listed anywhere. But on page 8-9 of my trusty service manual they talk about it. AARRGGHH!! :)

So as I see it I have two options at the moment. Leave it alone and live with it, or pull the cam out and either remove the spring or try and frind a replacement from someone other than Honda. Any thoughts?

Is there a chance the spring could come out and trash my top end?

Thanks for the help all!

P.S. If I had the cash I would look into either a Stage 1 Barnums or HotCam. :D

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  • qadsan

Posted February 17, 2004 - 11:38 AM

#2

First make sure your valves are properly adjusted as they do fall out of spec after a while and can make starting your bike more difficult.

In regards to the auto decompressor from what I can remember, the reverse cam part of the decompressor will have some free play in it. The decomp clutch and the adjoining reverse cam were pretty tight, but the piece next to it (between it and the cam lobe) was loose with a good 1/16 inch of up and down play from what I recall. If your's is like that, then I wouldn't worry.

You can also remove the auto decomp system on the cam. Also, aftermarket cams do not support the auto decomp, so you won't have it anyway. If you're thinking about a cam swap, keep an eye out because you can find the stage one HotCam for under $100 at some places. Make note that the HotCam folks designed their stage one cam for a completely stock bike and their ratings are based on a completely stock bike, not an uncorked XR650R. To remove the auto decomp system, you'll need to remove the cam, then use a puller to remove the cam sprocket flange. Don't pull from the flange ears or they'll break off. Once the cam sprocket flange is off, the rest of the demp crud comes right off. You simply remove everything between the cam sprocket flange and the first cam lobe to get rid of it. The only thing left to do is to remove a little spring loaded pin in the cam that the auto decompression. Once you remove it, there will be a hole there and you'll have to fill it to keep the oiling system in check. Some people epoxy the hole shut with good results, but I prefer a quick tap with the mig welder to seal it.

The downside to removing your auto decompression is that you won't be able to safely kick your bike over at any point, but will instead have to always find TDC, pull in the decomp lever, kick slightly past TDC, release the decomp lever and then kick as normal which is how 'most' people start their bikes anyways. With the auto decomp system, you can simply kick the bike over at any point and if the bike kicked back when trying to start it, the auto decomp would lift the right exhaust valve when the engine turned backwards to relieve the compression so it won't kick you back very hard when compared to what it could have done. The benefits to removing the auto decomp system from what I can see is that you don't have to worry about it failing (engine cutting out & difficult starting), less rotating mass on the cam, etc.





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