Alright, here's my situation: I can get a nice forged crank for a low price, but the counterwieghts are cut for a 5.7" rod, whereas I was hoping to run a 6.0" rod(I-beam) with a forged piston (dished). Is there going to be an issue with balancing? I would think a 5.7 rod/piston combo would be slightly heavier than a 6.0 rod/piston combo? I think that eagle cranks run the same counterweight for a 5.7 and 6.0 rod (probably not a good excuse, but an example). Would a good machine shop be able to balance it for a 6" rod? Its a real good deal, and if it took some extra machining it would still be worth it.
Thanks.

 

all else being equall a 6" rod would be heavier because of the additional length, the rod isn't the problems near as much as the piston needing to clear the counter weights. a good machine shop would be able to balance it for you.

 

Ede,
Thanks for the response. I think there would be more clearance for the 6" rod because it is longer and there is less piston height? I could be wrong though, and I'm really not going to find out untill I mock it up. Anyway, just because I'm over concerned I went through two setups:
the weights for each are as follows:

5.7 rod = 555g and 457g for piston = 1012g

6.0 rod = 578g and 403g for piston = 981g

same I beams just different lengths and same pistons too except for comp. height. I couldn't find the small end wdight for each rod, but I think the balancing should be pretty close. Hopefully this isn't as big of an issue as I'm making it out to be.

Thanks again,

 

thing to keep in mind is how much the piston moves, or how much stroke you have. that's fixed what does change is the wrist pin location and how far in or out of the hole the piston is at TDC whick would be a factor in piston clearance around the counter weights.