Help on Bobweight card

[Drewster]

Does this bobweight card look right? the balancing shop said the bobweight looked too high. they thought that it could be that i can not use 2 rods per throw on a Buick crank.
Im using Molnar Rods, Diamond pistons .020 over for a 4340 steel crank
any help or input is much appreciated, the crank is in the shop now and i would like the issue cleared up asap.
see pic


Andrew

 

[Drewster]

Anyone remenber what their bobwweight was? 1 piston per thow comes out to be 860g and 2 pistons per throw comes out to be 1717g . not sure which to use. heres the 1 piston per throw balance card. which is correct?

Andrew

 

[earlbrown]

Looks wrong to me. By having a bobweight that's for a pair of big ends, you'd have to choose one journal or the other. There's no way to bisect the difference between throws (as far as I know)

Caveat: A crank balancer is one machine I've never ran. I just know the math and the procedure.

 

[ek02]

The second card looks more like the last three engines I had balanced with similar crank and rods. The bob weights were 843 to 851 depending on the brand of parts. I think the bob weight gets split between the two rod journals from what I understand. By that I mean bob weight divided by 2, then that weight bolted to each journal on that throw for the total bob weight.