WD9 003thou undersize main bearings

[anglo4]

Anyone out there have any experience using the first factory undersize main shells of + 3 thou. According to the book, these were made as a first refit without removing the crank and to take out a bit of slack. The bearing surfaces are standard size and pretty good although the shells have had 65 years of work....! Comments please..

 

[gene bender]

You need to plasticgage the journals to see how much wear you have. Your bearings are oversize to compensate for the wear on the crank as the crank wears the bearings need to be thisker not under size. Some 2over are available for some engines you just need to check if they are any for that engine. I did find some for a Cub. There are several bearing suppliers selling inserts just need to find if there are any for that engine.

 

[rustred]

not going to work, waste of time trying, asking for trouble.if the crank is worn that much to accept those undersize brgs, it will be worn egg shaped. the crank does not wear equally all around.
the reason they are called undersize brgs. is because the crank is worn or turned undersize, not oversize.

 

[gene bender]

Yes when the crank wears the bearings are oversized cause the crank is now undersezed there are no undersize bearings

 

[riverbend]

It works, but causes modern mechanics to have a stroke.

When I took my H apart it had shims behind the crank bearings. When I put it back together I installed new bearings and new shims. Plastigauge checked good and it has been working most days every summer since then. I don't remember what year I did it, but there are something over 2000 hours on the motor now. Oil pressure is still good.

When I have to look at the motor again I will have the crank ground, if there are bearings available. Otherwise I'll have the cranks welded and reground to standard.

Greg

 

[Janicholson]

If you measure the journals across their diameter (crank out) in 6 places and across the journal's length, and it is cylindrical and has no deep groves or more than .001" difference in readings, it will be best to use standard bearings. (modern oil, changed regularly will actually prevent wear for a long long time, as much as 10,000 hours) If using plastigauge, The real taper or EGG shape will not be clearly measured. Putting undersized bearing inserts into a standard diameter journal location, it will wipe the insert, or lock the journal. Clearance of .001 to .0015 is as tight as reasonable. Jim

 

[Owen Aaland]

(quoted from post at 13:09:58 12/07/15) Yes when the crank wears the bearings are oversized cause the crank is now undersezed there are no undersize bearings

I think you will find when you go to purchase bearings that if you specify an oversize bearing it will have a larger OD to compensate for an oversize bore in the block or rod. Not very common these days. Bearings for undersized crank journals are referred to as undersized bearings.

 

[rustred]

ooh yes there is UNDERSIZE brgs, as that is what they are called when you order brgs. for a turned crank. they are NOT called OVERSIZE. how can the brg. be called oversize when it is thicker and has a smaller diameter circumference to fit the crank. where did you learn this from?

 

[Deutz Lover]

They are called undersize because they are thicker and therefore fit a smaller size journal. That is the way they list them. I know it sounds to some as reverse logic, but look it up. I did not know the .001" and 0.002" bearings were available for some engines until:

I was working on a Farmall super C C123 engine which had low oil pressure. The bearings read about .004+ clearance. I thought I was going to have to have the crank turned, but when I checked on bearings found that .002" undersize were available.

I did check the journals and was surprised I could not find any measurable taper or ovality. I had found this previously when working on a car engine. As it turns out the oil pump was mainly responsible for the low pressure. The aluminum cover on these engines are prone to warp and this also had to be addressed.