Crank shaft pulley wobbles

R

Rusty Karz

Member
I noticed a wobble in the crank shaft pulley that drives the belt for accessories. Is this normal or is it indicating imminent catastrophe?
 
Rusty Karz said:
I noticed a wobble in the crank shaft pulley that drives the belt for accessories. Is this normal or is it indicating imminent catastrophe?
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Can you begin by telling if it is a one-piece, -or a two-piece pulley? Many of the two-piece were manufactured where they were too short to allow the crank ratchet nut to adequately tighten it. Also, has this just started to occur or has this been ongoing for awhile??
 
ot normal at all. Is the crank nut loose? Put the crank in place with the engine off and transmission in gear, parking brake set. Turn the crank to spin the engine. Did the handle rotate? If so pull the crank hard until no rotation. then recheck. If it was just a loose nut you should be good to go. If it still wobbles you need to find why and repair until it doesn't wobble. Just mho
 
Appears to be a two piece. Doesn't seem to be loose in any way. I have a feeling it has been this way for a long time. I was timing the engine and noticed it today. I looked at some you tube videos of running Model A engines and some of them had the same wobble. The ones that had just been rebuilt did not. What size socket would I need to try tightening it?
 
Daveymac29 If I understand you correctly the crank will tighten the pulley? It seems tight as I was attempting to turn the engine and finally realized I still had it in gear. There was no noticeable slack when I was trying to crank it over. I took it out of gear and proceeded with the timing operation.
 
Harmonic imbalance is the cause of crankshaft pulley failure. Harmonic imbalance is also cause of main bearing failure due to torsional vibration, the crankshaft vibrates like a tuning fork. Harmonic balancers are available and do make a difference.
 
rusty karz said:
appears to be a two piece. Doesn't seem to be loose in any way. I have a feeling it has been this way for a long time. I was timing the engine and noticed it today. I looked at some you tube videos of running model a engines and some of them had the same wobble. The ones that had just been rebuilt did not. What size socket would i need to try tightening it?
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1 3/8
 
There is a special washer the venders sell that allows the crank nut to actually mate against the pulley. Assuming that when you tighten it, it doesn’t draw up tight. I personally wouldn’t use the two peice, as they have a lot of problems.
 
I can't see a wobble being caused by it being loose. They fit rather snug on the shaft. My first though is that someone smacked it against the cross member while pulling the engine and bent it. Don't know how much it would bend before breaking, if at all, being cast but sounds bent to me.
 
Licensed to kill said:
I can't see a wobble being caused by it being loose. They fit rather snug on the shaft. My first though is that someone smacked it against the cross member while pulling the engine and bent it. Don't know how much it would bend before breaking, if at all, being cast but sounds bent to me.
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That sounds about right to me. I have looked it over pretty good and it is not loose at all. It just has a little run out when turning. Probably been that way as long as I have owned it. I will probably see about getting a new one. Thanks for the reply.
 
Keep in mind why the front pulley failed in the first place,and why vendors sell two piece ones..they will work loose from vibration,in fact crack and fly apart..
 
The reason crank pulleys come loose according to McGee and McGee (model A engine rebuild, and Les Andrews mechanics book, is, as I stated above. The nut doesn’t tighten down correctly on the pulley. Both books make a point of verifying the nut actually rests on the pulley when tightened. Also I think it was commented on regarding torque in the recent connecting rod and main bearing thread, that torqued fasteners don’t come loose. The pulley is an 80# torque value. If the fit is correct, and it’s torqued, it won’t come loose.
 
Paul Bjarnason said:
Pray tell what vendor offers a harmonic balancer for a Model A motor. Thanks.
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Murray Horn in New Zealand. Excellent piece. horn@xtra.co.nz

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You have a defective front pulley and it needs to be replaced.

The dampener from Murray Horn can be ordered without the spiral grooves if you have a modern seal in front.
 
Tightening or loosening the nut on the front of the crankshaft should be done with the car in high gear. If you have an overdrive, put that in high too. You will need to apply 200 foot pounds. You can also tighten the front nut using the hand crank by hitting it hard with your foot or other object, but do that with the car in neutral. The impact will be absorbed by the flywheel.
 
Rusty - I had the same problem you describe - wobble on the two-piece pulley that was previously installed on my pickup. Upon removal I discovered that the bores on both the outer (front) and inner (engine) pieces were 0.009" larger than the shaft. Pronounced wiggle, very sloppy. In addition, the notch where the two pieces connected had a lot of play in it as well. I replaced it with a well-made, one-piece that fit very well (close slip fit, went on smoothly with no wiggle, bore on the new pulley was 0.002" over, which is much more what I would expect) The wobble went away. I did find that the new pulley hit the front engine mount and I had to relieve the mount just a bit to clear.

I suspect the previous owner installed the two-piece pulley around 1980, don't know the source but there may have been some bad parts circulating around about then.

JayJay
 
IMO, the pully was probably bent when the motor was installed. How many miles ago was that?
It's easy for others to spend your money but if you've done a lot of miles on it, I wouldn't get too excited.
 
I agree with Syncro, if it's been running that way quite a while and it's not loose or leaking, leave it alone. It's only job is to drive a big soft V belt and the belt doesn't care. If the engine has a stock Model A crank, balance is not an issue as nothing is balanced anyway.

If the engine was out for some reason, I'd probably fix the runout, but otherwise it seems like a lot of work for no real improvement.
 
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