"Normal" Press Fit

[DanStokes]

I'm still fighting with the pilot bearing on the Benz Diesel. The bearing keeps wanting to go in slightly crooked and will not press beyond the depth roughly equal to the thickness of the bearing.

After screwing up my 3rd. bearing (at least I have a local source now at $4.65 a pop) I got fancy and dug out the calipers. The hole in the crank was 1.360" while the bearing OD was 1.375". I took the green wheel (sort of between a mild grinding wheel and a polishing wheel) to the bearing and the die grinder with a Tootsie Roll and polishing roll to the crank bore. The readings now are 1.367/8" for the bore and 1.370" for the bearing OD. I'm remembering about 0.002" as a "normal" press fit on a bearing around this diameter. Is this correct or is my rememberer way off?

I could keep going with the die grinder but I don't want to take much more off the bearing as I have no way to know if it's concentric. Of course, I can't be sure if the crank hole is concentric........

I'll hold off on messing up my last bearing until I hear from you guys.

EDIT: I forgot to mention that there's no mention of a spec in the Haynes manual (evidently the Brits don't use pilot bearings) and the Benz forum I'm on makes no mention of this issue other than to say that it's darn tight and take the die grinder to it - but they don't say how much.

Thanks

Dan

[JeffMcKC]

Throw it in the freezer

[BangShift McT]

Have you tried freezing the bearing to expand it?

[SpiderGearsMan]

bearing or bushing

[DanStokes]

It's a bearing. Freezing it will cause it to contract, making it smaller. I tried that with the first bearing but by the time I got it to the critical part (most of the way in) it had warmed up so I don't think it bought me much. I could, however, freeze the bearing, the socket I'm using as a pusher, and the bearing puller that I'm pushing with. If all the rig is cold it might hold temp a little longer.

Jim, it's a standard sealed ball bearing with about a 9/16-14mm? center hole and the 1.375ish OD (it's metric so the dimensions are approximate in inches). At least they're cheap now that I know my local bearing house has them. If it was a bushing I could have the OD turned down a tad - there's a shop here in town that'll do those little jobs for me.

The crank I'm using was fitted with the automatic but no specs are available (or I can't come up with them) so I don't know if the pilot hole in the manual trans crank is supposed to be bigger that the pilot hole for the torque converter. If my buddy still has the torque converter I'll measure the converter snout just for chuckles.

Thanks all for your input.

Dan

[NewEnglandRaceFan]

freeze bearing, heat crank a little, and work fast..

[BigBlockMopar]

Instead of the freezer, just use a can of gum remover spray on the bearing right before trying to mount it. Works way faster.

[Orange65]

Per Machineries Handbook, for 1.19"-1.58" diameters, the interference should be between .0003"-.0013" for a FN1 class fit (light press- permanent fit for a thin section). This sounds about what a bearing interference fit should be to me without pulling out a bearing book.

If you would like, you can look up bearing fits on line. Most bearing companies have their catalogs on line along with an engineering section that will give you the preferred fits. Just look for a bearing (ball bearing I presume) that has the OD you have and check to see what the fit would be.

[DanStokes]

Thanks! This is the exact info I was looking for. I'll open up the crank bore a little more, freeze the bearing, and squeeze the whole deal together. I KNEW 0.015 was WAY too much!

Dan

Per Machineries Handbook, for 1.19"-1.58" diameters, the interference should be between .0003"-.0013" for a FN1 class fit (light press- permanent fit for a thin section). This sounds about what a bearing interference fit should be to me without pulling out a bearing book.

If you would like, you can look up bearing fits on line. Most bearing companies have their catalogs on line along with an engineering section that will give you the preferred fits. Just look for a bearing (ball bearing I presume) that has the OD you have and check to see what the fit would be.

[Orange65]

Yep- .015" would be ok if it was about 30" in diameter. Otherwise, it would take a sledgehammer to get it together and the bearing would not move if you did.

The auto manufacturer must have changed the bearing used in normal production with the larger bearing being offered as a replacement part or someone screwed up with the replacement part number at the parts stores.

[Loren]

Yep- .015" would be ok if it was about 30" in diameter.

Dan, don't forget that a bearing is a multi-component moving part, which always complicates things. If you're having to take extreme measures to get it in there, possibly once installed it's being pushed on so hard that inside clearances are affected.. Meaning, if you jam it in there like that, just make sure it spins free afterwards.

[Mr4Speed]

I had the same problem with my Olds. Ruined the first bearing forcing it in there, had to hone out the crank until it pressed in with a reasonable amount of force.

[OldMachinist]

You know the "right" way is to bore the hole in the crank in a lathe so the hole is round and true. This bearing doesn't have much pressure and with the limited use it will get you will probably be all right with your die grinder fix.

[DanStokes]

I know I'm doing it "ugly" but I really don't want to pull the crank out just to open up the hole.

As far as tightening up the inner clearances - that's one of the reasons I pulled the whole deal apart. It just didn't feel right to me.

The root cause (I think) - I'm guessing that the torque converter pilot is a bit smaller than the OD of the manual trans pilot bearing, so the crank holes were different from the factory. The converter fit REALLY tightly in the pilot hole and took some prying to get it loose so that hole was even tight for the converter. This is typical German over-engineering - make all the tolerances minimal whether or not it improves the final product. I'll catch up with my buddy and see if he still has the converter so I can measure it.

After researching this swap on the Interwebs, no one mentioned this "issue" so either I have a one-of-a-kind deal or lots of folks have slain this dragon but no one wrote it up. I'll be sure to do a post on the Benz forum once it's resolved so it becomes part of our collective knowledge.

Dan

[anotheridiot]

you are right, press fits were always .002. Now I have customers that want slip fits of .0002 so they dont break a nail pushing the bearing in a bore. My guess is the automatic crank was not reamed for the bearing, just primary machining of hole and not final machined, which is why you cant get a bearing in there easily.
All great suggestions, frostbite bearings on imports seem to be the norm.