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Discussion Starter #1
I've got my motor in my room for the winter since it has a rattling issue going on. Has 16k miles on engine, 1k on new piston. Air intake with exhaust, ran lean for 15k miles.
Engine has been ran hard most of its life while taking caution to let it warm up. Valves are also adjusted.

The top side of the piston sleeve where the cam chain runs through, has marks. I'm not sure if this is normal or not? If it isn't, should I replace the tensioner, or more than that?

My original goal was to replace some internal bearings, and to see if I can find anything that may have broken off inside the engine.
I suspect it may be a bearing issue since this person had an issue aswell. https://www.reddit.com/r/motorcycles/comments/7mz6kg/my_2015_grom_at_just_over_7300_miles_of_all/


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read or look up my old posting,

Get yourself the Koso cam chain tensioner arm and GromFatherZ cam chain tensioner adjustment unit and be done, best money spent to solve your cam chain problem.

Also do yourself a favor and lap your intake and exhaust valve and do a port matching of the intake pipe tube I/D and also your exhaust I/D pipe.

good luck
 

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what does the cam chain tensioner top button and wheel look like? The stock rubber button and wheel are known to wear. I run a finbro CT70 wheel and nylon button with zero issues. Best of all auto cam chain tension like stock.


I wouldnt be spliting cases before looking and inspecting tensioner and idler wheels / button. I highly doubt anything inside the case (crank bearings etc) are bad.
 

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Discussion Starter #6
Couldn't get a great picture of the rubbers, however the tensioner rubber has some wear on it.
Also I have an old grom head (had to replace because I broke exhaust threads), and there is significantly much less cam chain wear compared to this new head which only has less than half of the mileage on it.

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Discussion Starter #7
I got the upgraded cam chain tensioner parts installed and threw the motor back in the frame. I've still got the same rattling issues
 

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I got the upgraded cam chain tensioner parts installed and threw the motor back in the frame. I've still got the same rattling issues

yep it will happen every time until you put a adjustable cam unit like the one GromFatherZ makes or JapanWebike has something similar.
 

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Preferably, you pull the stator cover off and the stator, then you have full view of the cam chain and the guide wheels. This is probably the safest method to adjust the CCT and see how much deflection you have. I dont remember what I set it to, but I left maybe 1/4" or slightly less of deflection in the chain. I have heard that if you hear "whining" at higher RPMs it's too tight. I figure, as long as you leave some deflection and parents actually applying any undue pressure on the cam chain, you will be OK.
 
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