D rod bearing shims

dacaseguy

Member
Does anyone know how thick the original rod bearing shims would have been on a 42 model D. It shows three shims per bolt on the rod caps in the parts book. Dick, OR.
 
its not so much as how many, its till you get the correct clearance. need plastiguage and patience. need same amount on both sides. there is also different thicknesses in the pack. with these old tractor there is bound to be less than original amount unless pan has never been off. i have a d case that the pan was never off. too much of a pain working through the inpection covers.
 
I don't plan on pulling the pan. Looks a little difficult to plastic guage through the access holes? I was hoping to just put back what came out but some of them were distorted and I found a couple stuck together so I could not really determine what was in there before. Dick
 
well thats kinda a hit and miss no brainer thing. you are going to have either to loose or too tight brgs. pulling the pan is the answer. you need .015-.025 max clearance. how are you going to know this??? foolish idea. the idea of those shims is to remove as wear dictates. just guessing is nuts. too tight and you will burn the rod, too loose and you will knock out the babbit, so its your choice.just giving the reality of this.
i have spent many many hrs. just working to to get clearances correct with used cranks and brgs. new brgs and crank is a lot easier than used to set up.
 
Rustred, I think you needed to add another 0 after the decimal point. At least on car engines the 1 1/2 (0.0015) to 2 1/2 (0.0025) thousands of an inch is what I remember.
 
oops yes, i missed a zero. you are correct. .025 is like a spark plug gap, she sure would have a mean knock.
 
(quoted from post at 20:12:52 08/05/15) Does anyone know how thick the original rod bearing shims would have been on a 42 model D. It shows three shims per bolt on the rod caps in the parts book. Dick, OR.

Whenever we needed to adjust clearance on DC rods we would use the hammer handle test. After we got the rod cap torqued on we would try moving the rod from side to side by tapping on it with the end of a hammer handle. If it moved with a light tap, or you could wiggle it side to side by hand, it was too loose and needed a shim removed. You had to be able to move the rod with a sharp rap with the handle before it was good. That's the best I can describe it, but that's how we did it.
 
Keep in mind that bearing wear is typically not uniform around the circumference because the high load of the power stroke is in line with the rod and on the rod portion of the bearing. The bearing in the rod cap is only saddled with pulling down on the piston which is a lower load. The horizontal or side load on the rod bearing is quite low. Therefore, visualize the rod bearing to wear into an oval with the oval standing vertical.

For similar reasons, main bearings experience the high load only on the main bearing caps and the wear oval stands vertical.

Crankshaft rod bearings become "flat" (oval shaped) with the high wear on the portion that takes the load of the power stroke. The actual situation is the male and female portions of the bearing form two ovals rotating about each other.

Because of the above, the engine needs to be rotated a FULL TURN after removing shims to see if it drags during any portion of the rotation. I keep removing shims until I sense drag during some portion of the full rotation. I then add back one shim at a time until the drag disappears. Once satisfied, I loosen that bearing cap to eliminate any residual drag. and proceed to do the next bearing. Once all bearing are adjusted the last step is to tighten all the caps.

It is a tedious job. There is a saying that applies here. The pain of doing it right does not linger near as long as the pain of having done it wrong.
 

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