The pilot bearing on my 123 4 speed was seizing.
I replaced it with a 6202 ZZ C3 ball bearing.
That is what the previous owner had installed as I could read the numbers from it.
It was no longer working correctly and was preventing a smooth engagement of the non-synchronized reverse gear. It was taxing the other syncros as well.

Once I had the old bearing out, I used a round piece of stock that was machined slightly cupped so that no load was placed on the inner race as the bearing was installed. A socket could be used to do this as long as it catches the outer race.
It also became seized immediately upon installation. As did the next 3 new bearings.
So I decided to measure the inside diameter of the crankshaft and the outside diameter of the pilot bearing for a better understanding of what was taking place.

The bore of the crankshaft is 1.3735 inches using a Vernier micrometer.
The outside diameter of the bearings is 1.3775 inches.
Those numbers give a 0.004 interference fit.
I can tell you from the experience of trying this 3 times, that is too tight. No problem actually driving the bearing in place, but the outer race obviously becomes smaller, and jams up the balls once it is installed.

So taking a clue from others on this site, I carefully ground the outer bearing race diameter to achieve a less tight fit.

I have a scotchbrite wheel on my bench grinder. This could also be done with a fine belt on a belt sander or with an arbor held in a drill and applying light pressure against some fine sandpaper backed up with a very flat surface. I held the bearing between my two index fingers and let the scotchbrite wheel spin it. I placed a slight drag on the outer race with my thumbs and after two iterations, letting it cool between, I managed to remove 0.003 inches from the diameter and installed the bearing with 0.001 interference fit. The inner races spins freely at this setting. My final outer diameter was 1.3745. I did not use any locktite, but in retrospect, I wish I had applied some red or green. Time will tell if 0.001 inches was the right fit.

I suspect this engine was used with an automatic trans originally and maybe was not final clearanced for a pilot bearing. Not that the bore is rough, just may not have honed it to final size. Maybe some of you have more insight into this than me.

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Turbo300Mercede
87 300D W124
83 240D W123
80 300 TD Wagon W123, 4 Speed from 79 240D, SLS Rear Suspension

I hope you wore safety glasses ! .

BT, DT .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Good job!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The pilot bushing from the early Chevrolet S10 pickup, which is made of bronze, will fit that smaller hole just right. A bushing typically wont last as long as a bearing, but under normal use will last a long time. I did a freeze shrink of the correct pilot bearing from a pre 85 engine into the 85 617 turbo I put in my 240D. Pulled it two years later, not to many miles on it, probably 5000, and it looked like new.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Good information. Thanks for sharing.