37' A crank specs?

I'm overhauling the old 37' A that was bought brand new by my great grandpa and was the first tractor on our farm with rubber tires.

Anyway, my service manual still has not shown up yet and my machinist really needs the specs for he can get everything out of his shop.

What is the rod journal diameter and the oil gap on the crank?

Thank You.

Factory Farmer,

I took a look in the chart included in the JD Service Bulletin compilation put together by the late great Duane Larson, and it gives the diameter/tolerance for the connecting journal as 3.000 -2 The bearing itself is 3.002. This would be for A tractors between serial number 410000 and 487999.

The shims used to adjust the bearing are .003 inches thick, and that is a fair average for the oil clearance, as the rods are adjusted by removing shims until the crank drags, and then putting a shim back in.

You would do well to pick up a copy of the service bulletins. They are about the only place that you will find good information on the unstyled tractors. Nancy Larson sells the CDs.

Kurt

A few more tips:

Most auto machinist these days don't know how to deal with babbited bearings. There is a LOT of adjustment to be had in these bearings by using the shims. The crank can also be significantly out of round (5 or 8 thousands) and the bearings can still be adjusted with the shims and everything made fine without turning the crank or getting new rods.

The biggest problem would be if the crank were gauled up or if the journel was tapered from one end to the other. If the babbit is coming loose from the rods, this would also indicate getting the rods rebabbited.

Many times the crank can just be polised with 220 and then 400 emory cloth, and the babbit gone over with 00 steel wool.

If you have to get the crank turned and the rods rebabbited, you will just want to have the crank turned the minimal amount to clean it up, and then have the rods rebabbited to fit the crank. All rebabbiting is custom now, so there is no advantage to turning the crank to some standard undersize dimension. Just turn it the minimum amount.

Paul's Rod and Bearing is the place to call about this. They will give you the straight story. I called them because I thought I needed new rods, and they talked me right out of it. I did what they said with regards to polishing the crank and babbit, and my 37 B runs like a top.

Good luck,

Kurt

In the old days, there were some .001"s in that shim pack, and if there are not, you can add some.

Your machinest will find that your crank is egg-shaped. That's normal for these old two-cylinders. Just adjust the rods by the shims. Remove 1 at a time until the rod gets tight, then put 1 back in. Should be .003

Thanks everyone for you help! This is really the first time I have rebuilt a tractor with this type of bearing and I did not know what to think.

The crank is perfect but one of the bearings is marked up a little but the bearing is not coming off of the rod. Should this be cleaned up at all or not? Am I really over thinking this? I really can't think of a way for the machinist to clean it up with out really screwing me over when I go to put it back together.

I have a powerblock, pistons and rods that were pulled out of a running 1940 G and the bearings on those rods actually have an 1/8 in. deep piece missing out of the middle! Maybe my A rods are not so bad?

I guess I do not know what direction to turn....

A few scratches or discoloration in the babbit will not hurt a thing.

What I did was set my crank up on my bench with blocks under the mains so I could rotate the crank, and then measured the rod journals. You will want to measure at each end of the journal to see if it is tapered, and you will want to take measurements in the same place 90 degrees apart to see how egg shaped the journal is.


Assuming your happy with the result, then you will want to polish the journal with emory cloth.

The babbit can be lightly polished with 00 steel wool. Don't try to remove the scratches, they won't hurt anything. just get it smooth.

The next thing is to go ahead and fit the rods to the crank and adjust the shims. Hopefully you have kept track of the shims and caps. The left cap needs to go with the left rod, and the orientation needs to be correct. The cap and rod should be punched with one dot for number one cylinder, and 2 dots for number two cylinder.

Start out with an equal number of shims under each end of the cap, and remove a shim from each side until the rod drags, and then put one back. You will need to torque the cap to spec at each trial, and spin the rod all the way around, as it will likely drag only in two spots 180 degrees apart.

When your happy, take it back apart, keep up with the shims and then install. The adjustment can be done in the tractor, but if you have new piston and rings in a fresh bore, it can be difficult to tell when it drags.

Good luck,

Kurt

(quoted from post at 13:04:41 07/12/11) A few scratches or discoloration in the babbit will not hurt a thing.

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Thank you very much Kurt that is really what I wanted to hear right there!