Bob weight tolerance

Is there a bob weight tolerance for an external crank?

Bobweight is determined by a measuring the weight of the parts and using a formula. What you have to watch is the weight difference cylinder to cylinder. Seen some factory stuff off 10 - 20 grams and be just fine. Most shops try to match everything within 2 grams.

Steve

I've read several posts and articles of balancing an engine's rotating assembly and it's related parts. I have never understood why a so-called "balance job" is allowed to be OK! Is it balanced or not? Here at the shop we balance all components of the rotating assembly except the crankshaft, harmonic balancer and flywheel. Those items are "outsourced" with very specific instructions. We (my shop) are by no means perfect, but I think a "balance job' should be balanced not "good enough"!

Just more of my B.S.,
Dave.

LivermoreDave wrote:I've read several posts and articles of balancing an engine's rotating assembly and it's related parts. I have never understood why a so-called "balance job" is allowed to be OK! Is it balanced or not? Here at the shop we balance all components of the rotating assembly except the crankshaft, harmonic balancer and flywheel. Those items are "outsourced" with very specific instructions. We (my shop) are by no means perfect, but I think a "balance job' should be balanced not "good enough"!

Just more of my B.S.,
Dave.

Depending upon the specific job, balancing can be correct with anywhere between 47% to 54% reciprocating weight when figuring the final bob weight.
What is most important is that the front and back be identicle.
The factory crankshaft is balanced to a vast allowable tolerance; about an once and a half, (around 40 grams).