by KevBrewDog » Mon Apr 28, 2014 6:09 pm
Saw this thread. I bought a Hotcams Stage 1 cam for my 2006 CRF250X and was meticulous on following the proper install and break in. After the break in, I started the bike up (after cool down) and noticed a "clack, clack, clack" noise at idle. When I raised the RPMs on the throttle, the noise disappeared.
I began to troubleshoot and was able to determine the clack noise only occurred when the RPMs dropped below 1900 RPMS (I have a Hardline Hour/Tach on my bike). The clack noise is pronounced below 1900 RPMs, and if dipping down to the low 1800 RPMs, becomes so pronounced that the bike wants to stall. As soon as i raise the RPMs, the clack noise goes away.
I then checked my valve lash and was within spec for the exhaust (.012" and intake R=.00475" L=.006)
I called Hotcams and explained to them my problem and they said they did not have any other cases in their history of a similar type.
When I started doing more troubleshooting, I first replaced the cam auto-decompressor spring with a brand new Honda part. I made sure to wind the spring only 3/4 of a turn, just to get it around to stay on the flat portion of the end of the cam. This did not rectify the issue.
I then did some more "process of elimination" troubleshooting and removed the cam auto-decompressor (since I saw some email threads on this that it may be an issue with the little nub/lobe hitting the rocker arm lobe).
Next, I removed the auto-decompressor itself from the Hotcams stage1 cam. Surely enough, after removing the auto-decompressor mechanism from the cam, I was able to start the bike, and the noise went away. No clacking noise at any RPM level. I even adjusted the idle down to 1700 RPMs, and no noise.
I never had this clacking noise with my stock CRF cam (with the auto-decompressor attached).
Two questions:
1) I was wondering if I can run the bike with the Hotcams stage 1 cam without the cam auto-decompressor. The bike starts without it. Not sure if there are certain scenarios where the auto-decompressor comes into play in a key way (altitude, temperature, humidity, valve lash?)
2) Would the modification of grinding the nub/lobe(found in this article) resolve this issue?
Thanks for the support.