Fitting thin-walled Oilite bearings

[Clive FosterParticipant @clivefoster55965]

Ball sizing is effective but its not quite as simple as it seems, especially with Olite bushes.

Oversimplifying you are basically expanding the bush to increase the interference fit in its carrier.

The fact that the bore comes out the right size is, physically speaking, an incidental benefit. So, ideally you need to do the maths to ensure all the stresses et al work out properly or, better, follow established practice where someone has already done the maths and verified that everything works in practice.

One place where ball sizing is really handy is when you can't install the bush with enough interference fit for security e.g when you have to cold install in something that really needs to be heated to get the interference. Pushing the ball through gives you that extra hold. It also give you a bit more room on tolerances. In our sort of practice not vastly different to using loctite with the advantage that the bore comes out dead on and the surface smoothed out.

With Oilite ball sizing is essentially an alternative to using a mandrel to control compression on installation so you work to the same tolerances and sizes if you don't have any specific ball sizing data. Basically a mandrel increases the interference fit by reducing compression on installation whilst the ball gets the same effect by expansion afterwards. The important thing is not to apply so much force that the internal pore structure is significantly disturbed.

The compression on normal installation alters the pore structure but the bush is designed and made in such a way that the distortion produces the right structure so the oil moves as it should.

Oilite fitted without compression using loctite doesn't seem to work very well. The couple of times I tried that the Oilite bushes wore rapidly. Having a lifetime supply of "that size", which simply happened to be dead right for the repair job n question, I simply treated the replacements like simple bronze and oiled them on a sensible schedule which worked out fine.

It occurs to me that using loctite to repair fit bushes that have come loose for some reason ought to work better than using it on new bushes. The bushes will originally have compressed when fitted so the correct pore structure will have been established. Can't see any serious loctite migration into the bush happening and any outside sealing effect will surely not be vastly dissimilar to the effects of the interference fit from the housing wall.

Clive

Edited By Clive Foster on 01/10/2022 11:55:14

[Graham MeekParticipant @grahammeek88282]

My example of using Loctite to retain an Oilite bush was to show it does work. The amount of Loctite used would probably have only penetrated a few microns. Given most bushes have a 1 to1.5 mm wall thickness I do not think this is going to seriously affect oil retention.

When a machine is stood idle because there are no spares, or the lead time for a replacement is days away. Then it is a case of needs must, or you have to turn patients away. The bush was later replaced with a new one, but the original was extremely difficult to remove. Not wanting to use a drift on such delicate machinery I made a dedicated extraction tool. This work being carried out at the next scheduled service.

Regards

Gray,

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