FRporscheman

Well I can't answer that since I've never had an engine "balanced" or talked with any machinists or builders about that.

But from what I've gathered, they carefully measure and remove material from the parts. I imagine they have nice equipment and machines for mounting and measuring. I don't know if spinning is involved. In the end, the distribution of mass is less lopsided so it will vibrate less. The idea is to bring the center of mass (aka center of gravity) as close to the spin axis as possible.

Why wouldn't you consider such an engine balanced? The BS kills the harmonics, and the reworked parts should have a near-perfect center of mass.

fastmover

when they balance the rotating assembly, they attach the flywheel and crankpulley/dampner, then they weight the piston, wrist pin, connecting rods and bearings. then they take that weight from the appropiate piston and rod assembly and configure a bobweight and attach it to the crank in the proper cylinder position on the crank, they do the same for all 4 pistons and rods, then they spin the crank with the bobweights attached, which will identify area's of unbalance, in which they remove metal in the crankshaft or add in the proper spots. they do this untill they reach the target unbalance or zero balance, which ever the spec or customer calls for. It is alot like balancing a tire, but for the rotating assembly. You can also have the assy weighed and all pistons and connecting rods matched in weight by removing metal from the heavier units to matched the lightest unit of the bunch. If you ever have an engine apart it is worthwhile to have this done it is not very expensive, it should also be a must if you use lightweight components.

Semper fi.

Vilhuer

I would bet 944 crank is internally balanced meaning flywheel and pulley are not included in crank balancing and they are zero balanced on their own.

Video shows how its done but in this case crank is externally balanced and thus flywheel is included.

http://www.youtube.com/watch?v=cxWp2J1WG0A

RajDatta

Bill, 5.5 lbs weight loss from pistons and rods seems very high. Do you have a source for this information? It should be easy to find out if its actually true. I just have a hard time believing that 4 pistons and 4 rods can save you 5.5lbs.
Just curious.
Raj

Vilhuer

Weight saving didn't come from pistons as 944 S2 and 968 pistons weigh practically same 490-500g IIRR. 968 rods are lighter but 5.5lbs / 4 = same as entire rod weight. There is no way that can be correct.

RajDatta

Thank you!
That is why I questioned that. It seems almost impossible.
Raj

FRporscheman

Raj, he meant the S2 damper pulley weighs 5.5 lbs.

RajDatta

I understand Arash, but he is also saying that enough weight was lost on the pistons and rods to warrant losing the 5.5lb vibration damper. I would assume the weight loss to be atleast equivalant to the 5.5 lbs for them to dump the damper.
Am I assuming incorrectly?
Regards.
Raj

FRporscheman

Raj,
This is how I understand it. I don't think 5.5lbs necessarily needs to be removed to enable deleting a 5.5lb damper. It only takes a few ounces to set a rotating assembly off balance, and if you want to exactly counter this unbalance, you could remove a few ounces in the exact right place... or if you want to just muffle the vibrations you can make the whole thing heavier, thereby diluting those few ounces of unbalance. The larger total mass makes those few ounces less significant.

This is just how I understand it, might very well be wrong or incomplete... I've never seen the S2 damper pulley, but I assume it's just a symmetric weight?

333pg333

That's pretty much the answer I have been looking for. Not that I see that as being quite as perfect as the factory, but it sure sounds better than just chucking all these random items together and hoping for the best.