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Starting Problem? Like a Hammer knocking

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Hi, my '95 XR650L make a strange noise when starting up. Sometimes it takes a few tries to start especialy when cold, and then it makes a noise like someone hit the engine with a hammer... The engine is running well, im just worried about that loud "hammer" :smirk: sound during start up. What is causing this? or is it normal ( i doubt)

Thanks for any help.

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That sounds like either a piston slap or a rod knock. The rod knock might go away after oil pressure is built up. It it's more of a loud clicking noise from the top end, it'll be the decompression device, but you described it as a hammer sound. Hammer sounds aren't good.l

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Thanks, Can you tell me more about rod knocking?

Need more info to determine a possible cure for your problem.

How many miles are on the motor?

Does it only do it at start up and then go away?

Does it do it under load?

CW.

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Im guessing around 50000miles, but maybe around 20000 miles since the last overhaul.

Does it only during start up, especialy when the engine doesnt start immediately. It doestn happen on a regular interval, it knock randomly. I dont hear it when the engine is running, and the engine is running quite well. Could it be some decompression lever issuer?

Doesnt do it under load, only during start up...

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In my experience, if the decompression mechanism on the cam fails, it'll knock when it idles, stall and be hard to start. Not what you describe.

I'd check your valve clearances but I doubt that really has anything to do with it.

I'd say that the most likely thing is the piston skirt is getting worn and you get a piston slap at start up sometimes. It's probably quite due for a top end job.

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Thanks a lot for your help, the bike will be admitted in the hospital next week... ill let you know what it is... But at least i have a plus minus idea on whats going on...

Cheers

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