Gauging health of babbitt bearings

Steve in VA

Well-known Member
Richard G has been invaluable as I stumble along in restoring my Williams grist mill. He asked a question I can't answer: how are the babbitt bearings? Heaven knows I have no clue. I know babbitt in a theoretical sense so I throw my self on the mercy of the court.

This mill has 3 bearings. These 2 are incorporated into the frame so need to be looked at first. They seem to have minor pitting but no missing chunk or gouges. The upper halves are soaking in the parts washer. They have significant build-up of old, old lube. There were 2-3 layers of gasket between the halves so I conclude that they ran too far apart.

But, back to the issue at hand, how do I tell if these are ok to use?

The pics are not the best.the larger bearing that shows rust is where the end spacers rode that adjusted the distance between the stones.

In my opinion on something like that as opposed to engine bearings the main determination is how much play is in it? Then you need to make a determination of at what point does the play start causing the machine to do an ineffective job? Pitting etc, really plays a minimal part in the adequacy of a babbitt bearing, the pits in fact hold more available lube.
It sounds like I need to set the rotating element but that is a bit of a pain. But, if so then I can do it. I plan to mic the shaft and bearings next just to see how close I am.

2-3 thicknesses of gaskets may have been used as shims for setting the clearance.

When you measure the bearings measure in line with the direction the driving load of the rotating element pulled as well as vertical and horizontal in the bores, if it is not one of those directions.
I completely agree about the gasket
material. That would be the only way to
set clearance to my way of thinking.

The rotating element runs horizontal. One
stone is fixed while the other rotates.
The runner stone can be moved horizontally
a bit to set the distance between the

I just measured the 2 lower bearing
halves. I measured inner, middle, outer in
the horizontal. I also measured the depth
iding a metal rule and the mic again in 3

I haven't digested the numbers yet but
simply measured. Remembered, and recorded
but they all seem fairly consistent to
w/in +/- 0.05 inches. Thos may be good
enough or not. I simply don't know. I will
repeat for the upper halves once they come
out of the parts washer.
You need to consider the shaft condition as well as the bearings. And it looks like the babbitt is separating from the frame on both. There should be a thrust surface for the shaft. What does that look like? Post more pictures.
Steve, those are in great shape.
I have poured a lot of bearings, most recently on a syrup mill.
I would shine those up a bit as well as the shaft.
Those small gaps in the babbitt are great to help hold some oil in them.
Take out shims until it locks it down and then add just enough so it will turn freely.
Years ago, I was in charge of pouring some huge bearings for a BIG coal conveyor at a foundry.
That was an interesting job.
JUst a guess. Use PlastiGage,I can't think a reason why it won t work to check the clearance.
Ya if they made plastigage that thick. The red stuff is the thicker one I think , but still u dont need to be that tight. Thinking around .020 clearance. They cant be much tighter or they will get hot in a hurry.
As others have mentioned, those bearings are in good shape. I've run worse in sawmills, shingle mills, and my 4-sided planer, all of which are more picky than your grist mill will be. And I know some old timers who would run them even worse than me.

It was (and still is) common practice to set a few pieces of gasket material or shim stock between the cap and base when pouring babbitt in the top half, as it allows for some clearance adjustment: you can remove a piece when they start to run loose. Some large/heavy bearings will be poured with no (or minimal) gasket/shim, and a piece will then be added after the pour to give sufficient oil clearance. Hopefully you've kept the pieces you took out and remember where they went. If not, you may have to play around a little to get the right clearance (you probably want about 0.002'' clearance, but in that application a thou or two larger probably won't hurt). I definitely wouldn't bother re-pouring those bearings.

Just make sure you keep the oil to them. Running dry even for a short period will cause them to melt out of their boxes and pick up on the shaft. The whole idea with babbitt bearings is that the shaft runs on a thin film of oil, and the shaft never makes full contact with the babbitt material.

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