Got a knock

After reassmbing my engine, I now have a Knock. Engine runs fine, other than the knock. Have had a very competent factory mechanic take it apart and he says it's coming from the top end. Thinking it might be auto compression release not working right or need to replace cam timing belt (has 300+ hours on it). Anyone run into this problem and solved it? Thanks!

I am assuming you have a CRF250X? If you do, you have a timing chain, not a timing belt. And yes, 300 hrs is about as far as you need to go with the stock timing chain...recommended to be replaced every 2nd piston (100-150 hrs per piston- 200-300 hrs total). Its good to always replace the decompression spring...they could fail too and are an inexpensive $3 part. Not sure what your knock problem is. Its really tough to tell anything without more information of what you have serviced and when you have serviced your bike.


Thanks man. Just ordered replacement cam chain, hew cam chain guides, compression spring. Will report back once I get this stuff installed.

I'm guessing the slide in the carb is banging around. My son's has done it all along...mine never used mine does it too. Listen in the airbox...I'm guessing thats it.


i thought my top end was coming apart the last time i rode,i then remembered i adjusted the chain,watched the chain slap on a long smooth straight and realized that the knocking sound was indeed my chain slapping on the top guard on my swing arm lol

Where did you order your parts?

I ordered parts from Midwest Action Cycle. Best prices I've found local or net, and service and delivery is top notch.

FOUND THE PROBLEM! Where the front cam chain plastic guide rests, at the bottom of the case, was broken off. The only way to see it is to remove the flywheel. The result is that the guide is free to vibrate and rub against the guide. It was a self-inflicted wound, as somehow the cam chain wrapped around it when I was reassembling my top end. When I kick started the bike, it snapped it off. Thanks for all the help, everyone! Hope this never happens to you!

Always make sure to rotate the engine by hand (via the kickstarter) with the head cover off before kick starting. You will be able to feel the bind by hand and will be able to fix it before you are ready to kick it.

If its the same tab you are talking about, you aren't the first one that has had that break on them. There is another post somewhere about someone JB welding it back in place.

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