The way of overcoming fly wheels sheering off - apart from the obvious (i.e., having them balanced, using hi-tensile bolts at the right torque etc) I've heard of dowel pinning the fly wheel.
Yes to my suprise as well I would have thought that cranks would be balanced on their own but there is this matter of "bobweighting". I have this book on engine blueprinting which shows "bobweights" added to the crank to simulate the weight of reciprocating mass of piston with rings, rods, bolts, pins. I'll dig out the book and post some extracts/send you some scans. Maybe its all bullshit? I recall that with lighter pistons it is the case that the counterweights are made lighter making for a lighter reciprocating and rotating mass. The lighter rotating mass makes for faster response (as does lightening flywheel - 'external balance').
All reciprocating components need to be matched. As rods have both rotation and reciprocation each end of the rod is weighed sort of seperately on a special balance.
I'm speculating now...For ever action there is a reaction... but the counter-weights on the crank are at different lengths along the crank and different points gets loaded on the power stroke - so does the crank twist - just a bit???
I'm no mechanic or engineer but can imagine a few grams reciprocating some 70/80mm (stroke?) could add up to quite a weight.
Mon, 20 May 2002 15:02
