Interference fit for steel bearing housing repair sleeve into aluminium

Webley91 · Sep 16, 2020

How much interference fit would be recommended for a 38mm OD bearing bore repair sleeve shown in the attached list? I would be installing it into an aluminium alternator housing (see attached image).

My intention would be to replace the raised bore side wall shown in the image with the sleeve. There appears to be enough material thickness to bore out from the damaged inside diameter of approx 35.5mm to 38mm to fit the sleeve.

The size of sleeve I would be using is 35 x 38 x 15.5mm

Also, what type of retaining compound (if any) would be recommended for this application? Expansion of the parts due to heat during operation could be an issue.

Thanks for any information.

HuFlungDung · Sep 17, 2020

About .002" interference. Aluminum wants to gall when you press the sleeve in, but at .002" interference, it will go in fairly well. Make the sleeve thin, so it can collapse as it goes in. I'd suggest 1mm wall thickness when finished. So in the rough stage, it would be a few thousandths smaller so you can skim cut a few thou out to finish.

Some guys simply loctite the sleeve into a slide fit. That means you can finish the sleeve completely and then lock it in with permanent fit loctite. Alternators can get pretty hot though, so I'd prefer the mechanical interference. I generally install with loctite anyways, as it can provide a bit of a lubricant film to get the sleeve in without galling up.

On a small bearing like that, I don't think I'd worry about the differential expansion rates. Lots of brand new motors have a steel insert cast in place and then bored.

Webley91 · Sep 17, 2020

Thanks for the reply.

The part shown in the list is the repair sleeve. It comes ready made to press into place.

I am hopefully collecting it from the supplier in the next few days. I assume it is made from hardened and ground steel as a bearing race would be.

crossthread · Sep 17, 2020

The ones that I have used were not hardened and ground. They were not designed to be a bearing race but only to contain the outer race. Yours may be different of course. I have always done it using a "snug" slip fit and green bearing retaining loctite. Haven't had one come back.

Webley91 · Sep 17, 2020

barbter said:
Out of interest how much bigger is the housing bore than the bearing.

It is unevenly worn to around 0.5mm (approx 20 thou) oversize on one side of the bore.

BoxcarPete · Sep 17, 2020

HuFlungDung said:
About .002" interference. Aluminum wants to gall when you press the sleeve in, but at .002" interference, it will go in fairly well. Make the sleeve thin, so it can collapse as it goes in. I'd suggest 1mm wall thickness when finished. So in the rough stage, it would be a few thousandths smaller so you can skim cut a few thou out to finish.

Some guys simply loctite the sleeve into a slide fit. That means you can finish the sleeve completely and then lock it in with permanent fit loctite. Alternators can get pretty hot though, so I'd prefer the mechanical interference. I generally install with loctite anyways, as it can provide a bit of a lubricant film to get the sleeve in without galling up.

On a small bearing like that, I don't think I'd worry about the differential expansion rates. Lots of brand new motors have a steel insert cast in place and then bored.

I just recently did a similar job for my snowblower drive pulley. It was spun really bad (bored just to cleanup was 1.462" on a 1.375" bearing) and I did my sleeve .002" interference to the cleaned up pulley and another .0015" for the bearing. First bearing pressed in really nicely, firm pressure on the 5-ton, but then the second one didn't want to go in. I needed to swap the press over to 12-ton and "hang" on it a bit. The bearings rotate smoothly now, but with a fair bit of drag and that has me a little worried that I went too tight for it.

Sorry to hijack, but it's almost an identical question.

Phil in Montana · Sep 17, 2020

Bearing fit .002 to tight, .0005 under to on size, the bearing will warm up and expand into the bore....Phil

Guest · Sep 17, 2020

Phil in Montana said:
Bearing fit .002 to tight, .0005 under to on size, the bearing will warm up and expand into the bore....Phil

The problem is the aluminum bore will expand and the repair sleeve will spin with that fit, trust me. I am not a mechanical engineer, did not play one on TV, nor stay at Holiday Inns, but I have made custom alternator casings and altered off the shelf ones back when I was playing Dualkit, who was killed off by the recession of 2008. Alternators get very hot. I would first try that .002 under as previously mentioned. Then try to find a replacement bearing and size the sleeve thick enough so it's press does not collapse the bearing. The grade of bearing needed will depend on application and load. Most of today's automotive alternators have cheap Chinese bearings in them that can be bought for $1 and change a piece in bulk.

Phil in Montana · Sep 17, 2020

I was talking bearing fit, the sleeve to housing can be almost anything he can press in. I have been repair motors and alt housing all my life...Phil

Guest · Sep 17, 2020

BoxcarPete said:
I just recently did a similar job for my snowblower drive pulley. It was spun really bad (bored just to cleanup was 1.462" on a 1.375" bearing) and I did my sleeve .002" interference to the cleaned up pulley and another .0015" for the bearing. First bearing pressed in really nicely, firm pressure on the 5-ton, but then the second one didn't want to go in. I needed to swap the press over to 12-ton and "hang" on it a bit. The bearings rotate smoothly now, but with a fair bit of drag and that has me a little worried that I went too tight for it.

Sorry to hijack, but it's almost an identical question.

You said snow blower, so I doubt your situation applies, unless of course the OP is an ice road trucker and that alternator is on his rig. Those thin walled castings expand and contract a lot with heat.

BoxcarPete · Sep 17, 2020

Dualkit said:
You said snow blower, so I doubt your situation applies, unless of course the OP is an ice road trucker and that alternator is on his rig. Those thin walled castings expand and contract a lot with heat.

I was not offering advice per se, but adding my own variation of the issue to the mix. I ended up with .003x interference and thinking that a snowblower is used in colder temps I would have extra temperature range to compensate for. I figured this was the cause of the spinning to begin with, 100°F around this size is .0007~.0008 differential, meaning from 25F outside to 225F on a hot-running bearing a 2 thou press is almost entirely negated, but now after feeling how much drag is on the bearings I'm second guessing myself.

1953chevB · Sep 18, 2020

Timken Manual Recommended fits
https://www.timken.com/resources/timken-engineering-manual/

Erich · Sep 18, 2020

With a 1,5 mm wall thickness sleeve of this size, about 80% of the press fit will end up in reduced ID.
You will need to size the sleeve after installation to get the proper bearing fit of transition to .0005 loose.
This effect is why boxcarpete has drag on his bearings.

Webley91 · Sep 18, 2020

Thanks for the further replies.

I collected the repair sleeve today and it is simply turned from bar stock. If I would have known this before, I could have made it myself.

The bearing is an NSK 6202 bearing (OD 35mm, ID 15mm, thickness 11mm) with an eccentric groove for a spring clip in the outer race. I assume that the bearing is designed to have some clearance in the bore to allow for expansion.

Phil in Montana · Sep 18, 2020

Thats what the c-3 is...Phil

Webley91 · Sep 19, 2020

I didn't phrase that last post very well. I meant a clearance between the outer bearing race and the housing bore. I assume by C-3 you mean an expansion clearance within the bearing?

The bearing is a lubricated sealed type. The "new" bearing I have looks to be quite old as in it has sat on the shelf in its packaging for possibly a decade or more. Does the grease inside degrade over time?

These bearings with the clip do not seem to be that easy to find. I was surprised that the alternator parts supplier had one in stock.

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