Turning a -04 644 into a 628

worstinfinland · Jan 24, 2015

Hey guys,

I've had a question bugging me for a while.

Is the 628 crank, conrod and piston a bolt-on part for the -04 644?
Thinking of doing this once I get rid of the 644 crank. It should last 100 hours more, will see if that's enough for the short but cold finnish summer. :giggle:

Then do a rebuild on fall when it's neither smoto nor spikey tire season.

johnyberg · Jan 24, 2015

Hi, you will need a 628 crank without any modification at all and you are ready to go. The piston is the same except the brand, the '04 piston is wossner and the 05-08 is elko, both have a 2mm dish. I had done the same a few years ago. It's worth to upgrade the balancer too from the earlier models.

worstinfinland · Jan 24, 2015

What about conrod? Isn't crank pin larger diameter in the 628?
Also what do you think about removing the counter balancer on the 628.

johnyberg · Jan 24, 2015

Yes, you need the conrod too. I have remove the balancer but on my 644 crank, i can't say for the 628. There is no problem removing the balancer, but you have to rebalance the crank.

worstinfinland · Jan 24, 2015

Well some people (bushie, lineaweaver etc.) say that it's useless on 628 and could be removed without rebalancing the crank and be better off without the cb, but if removed on 644, the crank needs a rebalance.

bushmechanic · Jan 24, 2015

if you remove the CB from a 628 with a elko piston (278gm) the balance factor is a bit low

so you could leave it in or re balance to about 0.62

Dave Clark racing in the UK has bearings for the CBs

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Turning a -04 644 into a 628

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