Quote:
Originally Posted by AlfonsoR
Yes, the design of the flat six crank maybe balanced, but you are speaking only in design terms that for example a flat six crank is better balanced than an V engine crank.
However, dynamically balancing a rotating part has to do with an actual measurement of how much in-balance there is in that component. If you measured this from one flat six crank to another coming off the assembly line after balancing you would get different measurements.
Some possible variables in why one crank would measure different in-balance compared to another could be:
1. variables in forging process
2. stacking of machining tolerances that locate and machine the journals
3. operator (human) variables such as how close one meets balance parameters vs another operator, etc
4. balance machine variables such condition of machine, machine sensitivity, etc
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I appreciate your viewpoint, but the crank is not installed without balancing at the factory. It is balanced at the assembly point just to take into account the factors you mentioned above. Then it is picked up by human hands (for all 993's) and put into the main bearings, the case is sealed, and it spends the rest of its days there, until someone removes it. If no carnage has taken place, it will retain the factory balance indefinitely. Now, for higher rev than stock application, one would want to bring the balance tolerance close to zero perhaps, but for a daily driver, an undamaged stock crank is fine.
The point about indexing is an interesting one. I think this is usually skipped because nobody wants to destroy the ferritic nitrocarborizing (Tennifer treatment) just to tweek the journals by a tenth of a degree.