Balancing crank assembly
Moderator: martauto
More questions! I have aquired some parts for my (eventual) 2.5 build. I have some m52 2.8 con rods with pistons and a lightweight flywheel coming courtesy of Magpie. The crankshaft will also be lightened if possible. It's a shame I can't use the pistons that came with the rods, they're in pretty good nick. I will be having the crankshaft, rods, pistons and flywheel balanced. Should the crankshaft damper/harmonic balancer be done as well? If the crankshaft etc. has had weight reduction, will the standard damper/balancer be suitable? I don't want to run without one. Any advise on balancing is appreciated.
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maggspower
- Turbo Farmer Tractor Driver
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Lightening is a great idea, it makes the most of what you've got. BMW really made a good job of balancing these, and after lightening you need to do the same. Its best not to go crazy when lightening so it can be brought back to balance. Just run the stock harmonic balancer, I have seen lightened and alloy ones not do the job they where intended to.
Once the crank has been lightened, it needs the flywheel clutch cover, and balancer bolted to it and then "dynamically" balanced, this means as it is spinning, much like wheels, but the horizontal span is much wider, also they balance by drilling or grinding the crank webs, have a look at yours it will have a varity of different depth holes drilled in it.
The pistons and rods can be balanced "statically", this means weight matched, and in the case of the con rods end to end as well. There is not loads to come off an m52 rod, but there is a bit.
The whole process makes the engine feel smooth when reved, and potentially increases the safe rev limit, although for this other things have to be considered. Like I said BMW made a really good job of balancing, which is one of the reasons the 6 is so smooth. So dont go mad, there is a good few kg that can go if you include the flywheel and you will certainly notice it
Once the crank has been lightened, it needs the flywheel clutch cover, and balancer bolted to it and then "dynamically" balanced, this means as it is spinning, much like wheels, but the horizontal span is much wider, also they balance by drilling or grinding the crank webs, have a look at yours it will have a varity of different depth holes drilled in it.
The pistons and rods can be balanced "statically", this means weight matched, and in the case of the con rods end to end as well. There is not loads to come off an m52 rod, but there is a bit.
The whole process makes the engine feel smooth when reved, and potentially increases the safe rev limit, although for this other things have to be considered. Like I said BMW made a really good job of balancing, which is one of the reasons the 6 is so smooth. So dont go mad, there is a good few kg that can go if you include the flywheel and you will certainly notice it