Bob weight tolerance

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Bob weight tolerance

Post  tconnection on February 26th 2012, 1:56 am

Is there a bob weight tolerance for an external crank?

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Re: Bob weight tolerance

Post  466cj on February 26th 2012, 3:51 am

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

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Re: Bob weight tolerance

Post  LivermoreDave on February 26th 2012, 8:59 am

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.

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Re: Bob weight tolerance

Post  Larry Williams on February 26th 2012, 10:01 am

cheers
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.
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Re: Bob weight tolerance

Post  rmcomprandy on February 26th 2012, 10:27 am

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).

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