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Old 07-31-2020, 02:11 PM   #1
Rusty Karz
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Default Crank shaft pulley wobbles

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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Old 07-31-2020, 04:00 PM   #2
BRENT in 10-uh-C
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Default Re: Crank shaft pulley wobbles

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Originally Posted by Rusty Karz View Post
I noticed a wobble in the crank shaft pulley that drives the belt for accessories. Is this normal or is it indicating imminent catastrophe?
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??
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Old 07-31-2020, 04:05 PM   #3
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Default Re: Crank shaft pulley wobbles

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
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Old 07-31-2020, 05:40 PM   #4
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Default Re: Crank shaft pulley wobbles

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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Old 07-31-2020, 05:48 PM   #5
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Default Re: Crank shaft pulley wobbles

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.
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Old 07-31-2020, 06:55 PM   #6
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Default Re: Crank shaft pulley wobbles

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.
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Old 07-31-2020, 08:10 PM   #7
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Default Re: Crank shaft pulley wobbles

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Originally Posted by rusty karz View Post
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?
1 3/8
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Old 08-01-2020, 12:57 AM   #8
Chuck Sea/Tac
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Default Re: Crank shaft pulley wobbles

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.
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Old 08-01-2020, 09:54 AM   #9
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Default Re: Crank shaft pulley wobbles

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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Old 08-01-2020, 10:29 AM   #10
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Default Re: Crank shaft pulley wobbles

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What size socket would i need to try tightening it?
Stock size is 1-3/8", the one on my '31 is 1-1/4", I have also heard that some are 1-5/16".
YMMV
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Old 08-01-2020, 12:23 PM   #11
Rusty Karz
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Default Re: Crank shaft pulley wobbles

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Originally Posted by Licensed to kill View Post
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.
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.
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Old 08-01-2020, 07:18 PM   #12
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Default Re: Crank shaft pulley wobbles

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..
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Old 08-02-2020, 08:56 PM   #13
Chuck Sea/Tac
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Default Re: Crank shaft pulley wobbles

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.
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