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Old 01-24-2012, 02:14 PM
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crankshaft key way damaged

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

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Old 01-24-2012, 03:58 PM
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As you know without a pic it's hard to comment on your specific crank. If the edges of the keyway are just buggered up a bit you can dress it up with a fine file. Then with a new key installed slip the damper/balancer on and draw it up tight with the proper tool (not a hammer and 2x4) if it doesn't move or wobble you should be good to go. Need the pics though to make sure.
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Old 01-24-2012, 04:21 PM
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Old 01-24-2012, 05:20 PM
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THe key is just there to locate the balancer. Having the correct press fit on the crank snout is what holds it on and makes the balancer function properly.
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Old 01-24-2012, 05:22 PM
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Quote:
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
It needs to have a 0.0005"-0.0015" press fit, IIRC. You could have the keyways opened up to 1/4", there are dual keyway dampers usually used on supercharged apps that will work if another keyway is cut into the crank snout. It might be cheaper to get another crank, though.
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Old 01-27-2012, 12:02 AM
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damaged key way

Ok, I got pic of the key slot. Not horrible but definitely noticeable and there is a slight bump/ridge on either side of the enlarged front portion of the slot.
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Old 01-27-2012, 08:34 AM
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That isn't that bad. I'd reuse it after cleaning the slot up real good, new key and just be damn sure the new damper is the correct press fit.
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Old 01-27-2012, 07:33 PM
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Quote:
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.

Bogie
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Old 01-27-2012, 07:41 PM
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Quote:
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
get it welded and then have them cut a new keyway its done all the time
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