'37 JD A crank

Navajo350

Member
I hope this is normal, but assume it is not...

A tooth missing on the crank
25260.jpg
 
Some were machined that way to "time" the original clutch driver to the crank. The driver had a bump cast in the one spline so it would only fit the crank one way.
 
(quoted from post at 14:39:01 07/31/15) Some were machined that way to "time" the original clutch driver to the crank. The driver had a bump cast in the one spline so it would only fit the crank one way.

Good to know, good to hear. Thanks.
 
If your photo is exact, the BUMP on the CRANK can be seen in your photo, but splines also give evidence of wear as they fit more exact than yours shows , closer inspection is WARRANTED.
 
That is the "balance" groove made that way so it can only go on correctly. What I am seeing tho is that the driver is on almost flush with end of crank and I believe there should be 1/8-1/4" before flush for clamping force of the bolt/washer. I gues if there is even 1/8" it should still clamp it tight on the taper. If it goes flush you may have an issue.
 
(quoted from post at 18:32:43 07/31/15) That is the "balance" groove made that way so it can only go on correctly. What I am seeing tho is that the driver is on almost flush with end of crank and I believe there should be 1/8-1/4" before flush for clamping force of the bolt/washer. I gues if there is even 1/8" it should still clamp it tight on the taper. If it goes flush you may have an issue.

What are my options then?

What happens if I leave it as is?
 
Leave it alone and eventually you'll need a crank and driver. Crank needs to be cut off or washer stack brazed to driver to return the clearance needed for the driver to be forced up onto the taper so it can NOT move as it did when it fretted the area under the bolt's washer. You'll have to keep a watch on it and re-torque the bolt when needed quite a lot until it settles into place and quits moving. Because it's less costly I would do the washer stack on the driver but the inner diameter of them has to be larger than the crank end by a good deal.

Might be better off trying on a few drivers first - this one is wore down pretty good. It's the crank that gets really pricey.

I think I can see the stem of the rivet serving the purpose of the 'bump' where bump is the rivet head?
 
(quoted from post at 20:07:02 07/31/15) Leave it alone and eventually you'll need a crank and driver. Crank needs to be cut off or washer stack brazed to driver to return the clearance needed for the driver to be forced up onto the taper so it can NOT move as it did when it fretted the area under the bolt's washer. You'll have to keep a watch on it and re-torque the bolt when needed quite a lot until it settles into place and quits moving. Because it's less costly I would do the washer stack on the driver but the inner diameter of them has to be larger than the crank end by a good deal.

Might be better off trying on a few drivers first - this one is wore down pretty good. It's the crank that gets really pricey.

I think I can see the stem of the rivet serving the purpose of the 'bump' where bump is the rivet head?

Does anyone have a photo of what one should look like?
 
No, the crank should never extend out past the driver. Driver should always be proud of the crank by some safety margin, so you might be OK there after all. As little as .050 might work, but the real problem will be that this dimension will shrink as the driver works it's way back up onto the taper where it's supposed to live. Because it was run with the bolt loose, it will want to creep up the taper constantly so you will have to keep re-torquing that bolt often to ensure that it doesn't work loose again and ruin things the expensive way. If you run out of safety margin I speak of you will wind up right back here with the same problem in the future. Sorry I'd have to take mine loose in order to take a picture, so I have no picture.

What worries me about your photo is the fretting on the end of the crank. How did that get there if it's below the surface of the driver? If this is due to the washer clanking about then I have no more problem with the photo - but it looks like to me that the end of the crank and the driver face are at the same height and this situation will NEVER work out good. Maybe it's just the picture. Were it mine, I'd get a tenth of an inch of space in there with a washer brazed onto the face of the driver, only then would I trust that there is enough space in there to compensate for the driver moving up the taper in the years to come. And I'd keep after that bolt until it stays good and tight.
 

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