750 and 850 cranks different?

bsaboss · Feb 9, 2014

I'm wondering if 750 cranks are different than pre-Mk3 850 cranks? I've got three or four perfect 750 cranks and if it's possible to do so I'd like to use of of them in an 850 engine I'm building, rather than finding/buying an 850 crank.

myjota · Feb 9, 2014

They fit no problem. Done it both ways 750 crank in an 850 and 850 crank in 750. Some 750 cranks are a bit lighter and liven things up a bit in an 850 probably balance related. You probably won't notice any difference.

RennieK · Feb 9, 2014

As I just posted in another thread the 850 crank is close to 5lbs heavier as I recall. 850 pistons are something like 80 grams different than 750 so you should have it rebalanced.

bsaboss · Feb 10, 2014

Many thanks for your advice. Good to know.

rvich · Feb 10, 2014

Just out of curiosity what do your cranks weigh? Got a scale handy? I notice the workshop manual lists one crankshaft with a balance factor of 52%.

Russ

myjota · Feb 10, 2014

You probably should get it rebalanced but in the real world it won't really be very noticeable on a street bike. I found 850 crank in a 750 took away that really crisp revving and sort of stifled the engine but 750 crank in 850 brought it to life! No noticeable increase in vibes though. Back in the 70s we didn't worry what the crank came out of as long as it fitted and was cheap enough and got the bike back on the road!

bsaboss · Feb 10, 2014

I'll get a set of scales and weigh them on the weekend. The idea of a livened up 850 via a 750 crank transplant is appealing.

750 and 850 cranks different?

bsaboss

myjota

RennieK

bsaboss

rvich

myjota

bsaboss

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