Originally Posted by red82c10
So I picked up a 307 crank to make a 327. Turns out the balancer key slot is a little damaged and could be questionable. Sorry I don't have a pic yet but in any event... what can be done to possibly fix it at a machine shop? Or is it better policy to just get another crank considering its importance.
FYI- mild street motor, 9:1, very mild cam, 193 heads, Qjet carb
Used to be the machine shop recut the shaft for the next size up key. There used to be stepped keys that would fit the new keyway and engage the old damper or gear with the original size keyway if that part was undamaged. If the attaching part's keyway was damaged it was either replaced or sent to a shop with a broach to recut it to a larger size.
But we live in a throw away society now, finding a place that does this will be difficult.
This type damage to the key or keyway is indication the part is not being held securly to the shaft. Given a 307 shaft I have to ask if the damper is head with a bolt. If this is one of those jobs that was a pressfit there really isn't a good solution without using a retainer bolt along with a light press fit.
This is such an old problem that comes around every generation or so. Harley and Porsche got themselves up this tree (again) with cam drive issues a few years ago where they tried to retain the cam drive gear with a key and nut but no press fit. It just never works, it isn't long before inertial lag and vibration between parts has the poor old key twisting back and forth slowly making its slot wider. You see this as pooched up material along the upper edge of the slot and if you could get into the bottom to measure it you'll probably find that's pounding wider as well.