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Loud metal thrashing sound?please help me diagnose!

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Ok guys I have here a 04 crf450r, I just rebuilt the top end. I bought it needing a new top end I was told,so I dont know any past history of bike.Nor have I ever owned a crf450, so I dont know their characterisitics....Here is the issue the bike runs fantastic...only issue is it makes a loud metal thrashing sound at low rpms only, and only is lower gears....also does it if I lug it really bad, and I notice it whenever I happen to stall bike at low speeds..ive been searching all over forums on web,,they all say this loud noise is coming from my chain slapping swingarm or case,front sprocket, chain slider..I have looked and adjusted chain twice now, with no improvement or change. It really sound way to loud to be coming from chain..its so loud it scares me to even ride the bike..I can say at idle and at any speed with clutch not engage(pulled in), the noise does not exist..And if im hard on the gas it does not exist..clutch works great doesnt slip or anything crazy like that...My guess is, the motor internally is fine...it would have to be something in tranny or clutch..I did read about spacer behind front sprocket for oring chain...I have not checked to see yet...but pleae I cannot be the only person with this issue....so chime in guys..so i can get out on the trails...aloha

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With the noise only coming while you are in motion, it sounds like "drive train" to me. I hate to say this but it sounds like chain to me. Its gotta be hitting something. If the noise is as loud as a chain hitting the swingarm or "louder"..... IMHO your bike would've self destructed already. Go through your "drive train" and check sprokets, aligment of chain and for any marks on the swingarm or cases. Try going to the "tight" side of the chain adjustment and see if it eliminates the noise. If so, theres your issue. If not, I too will learn something when someone else answers. Good luck

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You are going to have to ride another bike, or have another crf rider ride yours to see if it's a real problem.

These motors are noisy........

Chain slap has nothing to do with tightening the chain.

It is about chain alignment, and affixing the swingarm rubstrip to the swingarm so it doesn't vibrate or slap.

If you are using the stock chain block marks to adjust your chain, stop. You need new precision blocks, and to check them against the actual distance to the swingarm on each side.

 

Oh, and don't tighten the chain past the recommended slack or you will destroy the CS seal.

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When I bought my used crf450r I took it to my brother in law (bike mechanic)about what sounds like the same noise your experiencing he checked everything and said the noise is common on theses bikes

He pretty much said if I hear it I'm not riding it the way it's meant to be riden, that was 2 years ago

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Thanks for input guys,,the more i think about it has to be something not aligned I noticied the chain had 520 v on it..have yet to take it all apart and check for spacer..it does have aftermarket chain adjusting blocks..not sure of brand...but previous owner told me he had went through like 3 stock chain guides already and their are chain marks all over the tire hugger in front of rear tire..so something is not aligned..I noticied when adjusting chain it has alot of side movement but chain looks fine,and its not over tightened...I will keep everyone posted on outcome

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When I bought my used crf450r I took it to my brother in law (bike mechanic)about what sounds like the same noise your experiencing he checked everything and said the noise is common on theses bikes

He pretty much said if I hear it I'm not riding it the way it's meant to be riden, that was 2 years ago

+1......i notice my 07 does make a rattle putting around the yard or trails but on the track i dont hear a thing.

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If it is a slapping/skipping sound and it happens when you are lugging the engine really hard than it could be the timing chain that you are hearing. 

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Have you changed out the front sprocket to a larger one? If so that will change the height of the chain and its relation to the slider on top of the swing arm! Sounds small but it happened to me when I went from a 13 tooth to a 14. What fixed it for me is to keep fresh chain guides and rollers, proper adjustment of the chain, both alignment and tension.

If you plastic guard in front of the rear tire is getting chewed up, our chain is way to loose, plus that's a lot of lateral flex. Stock chain or replacement?

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Not sure if its a stock chain or not, I just bought the bike used and rebuilt motor, (also installed brand new timing chain)..so thats not the issue.Im going to put it on blocks tomorrow and find my issue...maybe chain is bent or warped and new one is in order...chain blocks guides are bad, or rear wheels is not in proper alignment, hopefully i find the culprit to my problem

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