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drill marks on crank counterweights #781547 08/15/19 3:36 pm
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tommy Offline OP
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I purchased a 1968 t120 and in the process of rebuilding the engine ive come across many issues. To my finding the bike was upgraded to 750cc and the timing side bearing was destroyed. I decided to bring her back to 650cc, but i have some concerns. The crank seems to have been balanced to some unknown factor. The counter weights have drill markings, 4 on the sludge trap side and 2 on the opposite (not including the factory drill mark opposite of the sludge trap). Ive been told that it should be ok to run as long as the balance factor is within reason. I just dont understand the drill marks on the counterweights. Do they effect balance across the plane of the crank? If one counterbalance it slightly lighter then the other, would it cause issues with the bearings? Any input and explanation would be awesome.

I have one more question regarding the drive side bearing race. I heated the case and the race kinda just fell in without much force. Im concerned that when the engine runs and gets hot, the race may want to spin. It it normal for the race to just fall into the journal with out much force? Could i use loctite 640 as a precaution?

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Re: drill marks on crank counterweights [Re: tommy] #781554 08/15/19 4:24 pm
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Balancing is as much, if not more, about side-to-side balancing as it is up/down. I've had a bike that would "walk" as it was so out of balance side-to-side. Some times, the holes can't be placed on the flywheel to remove enough metal (I think the factory limits holes to 3/16" depth) so drilling the weights takes care of this. I doubt this would be the cause of failure on your timing-side bearing.

Regarding the race in the case, heating is the best way to remove it from the case and I've usually had it fall right out as well. There isn't very much radial force against the race during normal operation that should be of concern (unless the race is loose without applying heat.

Re: drill marks on crank counterweights [Re: tommy] #781555 08/15/19 4:43 pm
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triton thrasher Online Content
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It will move a bit when it’s hot and that won’t matter.

Loctite won’t stop that happening.


Amateur Loctite enthusiast.

Moderated by  Alan_nc 

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