Another Main Bearing Question

[Anonymous-0]

Talked to the machine shop today about sizing new main bearings to my crankshaft. They suggested instead of machining the bearing to get the running clearance, they could leave the bearing (oversize) and turn the crankshaft to get the clearance. They said it would be difficult to perfectly set up and turn the bearing, but be a lot easier to turn the crankshaft instead. Has anybody ever tried this?

 

[D-]

Main bearing housing is easily set up in boring bar. Bearings are undersized and also shrink as pressed into housing. Wouldn't be wise to grind crankshaft to fit bearing.

 

[Mike(NEOhio)]

That's because they only know about grinding cranks. If you're talking babbitted mains then any machine shop could bore them in a lathe.

 

[teddy52food]

They will be turning off way more than should be. Then if there is ever a problem again, you will be looking for another shaft. That is not the right way to do it.

 

[JackieB]

Does he need to consider a more qualified shop ?

 

[skip33652]

The center of bearing housing usually not concentric to outside of housing. One must bore bearing so it is centered in outside flange, so it is perpendicular to the outer flange and so it is the right size. It would be best to use lathe with four jaw chuck.Paul

 

[Anonymous-0]

Thanks for the help. It sounds like I need a good machinist with experience. The last place I checked said they would try it for $75 per hour with no estimate on how long it will take. He said it will take time to get the housing centered. Does anybody know of a good shop in the Kansas area?

 

[Mike M]

I did one for a 50 once. Was easy to do. Clamp housing in a 3 jaw chuck and bore it out with a boring bar.

 

[gtx1967jewison]

RUN from that shop !!

 

[Earl-IL]

That is the correct way. That is the only accurate way it can be done, using a 4 jaw chuck. If you set it on parallel bars and bored it with a cylinder boring bar and it worked ,consider yourself lucky. When doing the diesel with the center main & we are grinding the crankshaft we always gave the center main the same oil clearance as the two outside bearings. We had many of them come through with the center main spun or worn excessively. When you change oil in your 2cyl diesel always be looking for the copper fleck in your drain pan.