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I think all the cranks on these twins are balanced to 85%. Not sure on yours but my 68 T120R called for that %. There was a thread awhile back discussing the pros and cons between Dynamic and Static balancing that goes into detail about what to weigh and how to come up with the figures. Do a search in this forum. Some good information. I had mine dynamically balanced to 75% and it is really smoother. I let a friend that has several Triumphs ride it this morning and he said it is the smoothest Triumph he has ever ridden. I don't know if or how much smoother it might have been if I'd taken it to 85%.
 

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Just reread some of the threads about crank balancing. The way I read it is: to arrive at the balance weight required, the rods are weighed at each end. The piston, rings, wrist pin, & circlips are weighed and that weight is added to the weight of the small end of the rod. They take 85% of this total and add it to the weight of the large end of the rod (weighed with all bearings, bolts and nuts in place). This total is the bob weight needed. This is done for the left and right sides individually and each piston, rod etc. is identified as the set it was weighed with so that they can be assembled with that group of parts and on the correct journal. For best results, the crank should have the rotor, sludge tube, and cam drive pinion with associated nuts, keys, and washers in place when balancing is done.
 

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Thanks for setting things right pookybear. I didn't know for sure so said "I think they're 85%". I must've been reading 750 specs when I told the machinist what figure to use when I had my 650 done. Are "ALL" the 750's done to 74% or just the short rod (are all the 750's short rod?)? If so do you know what years that would include?
 
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