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.... bored, ground, polished and all very clean. Cam lobes and followers need the attention of a Specialist grinder though. Camshaft bush's untouched as no disernable wear. After reading much about dynamic balancing have decided to go ahead. Is the correct balance factor 75%?

Thanks in advance.
 

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74 % is normal for a T140,according to the specs.It seems to suit the OIF.
If you actually measure some that run OK,they can be closer to 65%.

Dry frame 650 engines were factory balanced to 85%.They run OK between 65% and 85% balance factor.

The best advice I can give is tell them not to change the balance factor;just measure it.Then dynamically balance the crank to that balance factor.

I'd always spend money on crack-testing a crank,before I spend any more money on it.I'd spend money on TUFTRIDING a crank so it won't crack,before I spend it on balancing.I always make pistons equal weight,and rods equal weight (small-end and big-end),so the balancing is 2/3 done anyway.

Do some research on cam/tappet break-in.
 
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