Quote:
Originally Posted by Ruth
My thoughts as well. What if you ever need to change the pressure plate or flywheel. Are you going to disassemble the engine to re-balance the crank/flywheel/pressure plate togeter? Much easier to just balance the new parts.
|
Balancing as an assembly avoids the potential pitfall that tolerances may add to each other rather than cancelling each other out.
The way my tech does it, you start with individually balanced components (like Terry Burtz sells for the Burtz engine - balanced crankshaft and balanced flywheel - or balance the components separately). You then balance the crank plus flywheel to double check that you are still OK, , and come back to spec (if necessary) by flipping the flywheel or (if necessary) drilling the flywheel. You then add the pressure plate, and come back to spec by rotating the pressure plate on the flywheel, and if necessary add weld to the pressure plate. Naturally you mark all components for reassembly. That way you end up with the final product as close as possible. If you change the pressure plate without rebalancing in the future you are no worse off than if you had not gone through the assembly process originally, since the flywheel and crank assembly was balanced previously.
In reality, given the low rpms we operate our Model A engines (for the most part, I'm not talking hill climbers here), balancing each component separately and then assembling them without further ado has served many quite well, and is a way way improvement over stock.
It's sort of the same concept as we use in balancing reciprocating elements. We usually start by getting the rod small ends as close as possible, then mix and match pistons, pins and small end rod weights to get as close as possible, then tweak (usually the pistons) at the end to get balanced assemblies.
Truth be told, I have only done this on motorcycle engines. Have not done this on a Model A engine yet, but will do so when I finally get around to building my Burtz. I figure that I have so much invested in the engine that it's worth taking the extra step.