Quote:
Originally Posted by DorkMissile
Update - received the call from Tesar Engineering today - balance is now at .27gr, which I would think suffices.
We were "calculating" about 24-26gr of unbalance on paper. When he got it on the balancer, it came in at 18gr out of balance (with the crank being heavy). The scary thing is, looking back on this, is that the concept of "drop ins" really doesn't work. Well I guess it works given a large enough tolerance.
Talking about the concept of drop ins with my machine shop (he is a "old timer"), he says the only way it would work would be by accepting up to +/- 15 or 20 grams of balance in each direction. Like he said - we were "back figuring" what the factory bobweight should be based on what the factory rods / pistons / pins weighed, and it turned out that the crank was still 10gr or so lighter on the rotating weight than what it "should" have been based on the reciprocating parts
A couple of 3/4" holes about .5" deep is all it took. $260 for them to balance the assembly, the flywheel and polish the crank. Money well spent IMO.
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DorkMissle - This is another piece of extremely valuable data.
It clearly proves, that as suspected, the term "Drop-In" does not really reflect reality - especially when rods are involved as well.
I wonder if opting for Forged "Pistons Only" option and actually being able to source a set in which all the pistons' components, Incl. Pins, Rings, Clips (+ Piston itself of course), actually weigh exactly like the OEM piston assembly. Then we might get away with really dropping them in without having to balance the complete RA.
What is your take / your engine builders take on this? Would be interesting to know.