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Is cast aluminum OK for bearing cases?


Luv2Wrench

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I recently broke some cast iron bearing cases. While I can send these away to be reproduced, I'd like to give it a try myself. If I did this I would be using aluminum for the casting as it has a much lower melting point than iron. The bearings that would go in the case would be your typical sealed bearings that would be press fit. Is aluminum an acceptable metal for this application? Might I use bronze instead? Has anyone done this before?

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What sort of bearing cases? How much force is used on the bearings? More info needed to make a decision.

What he said. It all depends on the forces, the design of the case, and the quality of the aluminum used for casting. Every transmission made in the last 15+ years has been made of cast aluminum, so yeah, it can be strong enough if designed properly. The problem is that aluminum has one third the stiffness of iron or steel. If you duplicate a cast iron design in aluminum without regard for the stiffness differences, you may find that the aluminum casting spreads under load and changes either the bearing preload or the gear contact, with resulting failure. Few people who are not engineers really understand the difference between strength and stiffness. Aluminum castings can be as strong as iron, but for the same cross section they will only be 1/3 as stiff.

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Thank you for your quick replies. I didn't think about the other forces on the bearing case, I was asking more about the ability to press fit a bearing into aluminum.

I've attached two images that will hopefully provide some more details on the application of the bearing case. The first image shows the bearing case on the left with the bearing on the right. The holes labeled 1,2 and 3 are attached to the frame rail. Hole #4 goes to rod that connects with the rear axle. I believe the purpose is to keep the bearing case (and thus the gear on which the chain rides) a fixed distance from the axle (and thus the other gear on which the chain rides). As the axle moves vertically on the leaf springs this bar must force the axle to move slightly horizontally to maintain the same distance between the two gears and thus keep the chain from snapping or falling off. This is my own theory and I have nothing to back it up so it could be completely incorrect.

Hole #5 is connected to the frame rail as well but through another bar so that, apparently, it can directly offset the forces on hole #4. It appears (again, I'm making this up) that main force vector is applied to hole #4 and transmitted through the bottom section of the casing to hole #5 which passes it on the the frame rail.

The second image shows the bearing case attached to the frame rail and the holes are numbered the same as image 1. There are also two lines on this showing the bar connecting the rear axle to the bearing and the bearing to the frame.

I guess the main force on the bearing case is the amount of force needed to move the axle (and leaf spring) horizontally to offset the amount of vertical movement. Since the other side of the bearing is mounted to the frame rail, I guess the area of concern would be between holes 4 and 5.

There is an identical setup on the other side as both wheels are powered by chain.

post-65715-143139228911_thumb.jpg

post-65715-143139228915_thumb.jpg

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Little need for press fit,,Put aluminum on stove for a few minutes,,coverd by tin can,,

You'll be suprised with the expansion,,,,just drop the bearing in,,,

Bronze,,same expansion as ally' ,,

The rod from the axle-countershaft is called a radius arm or rod,,

as it forces the axle to make a radius around the countershaf,,

Is it worth considering welding or brazing the old parts??

Good luck,,,Ben

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Bronz melting point same as iron,,, +-- ,,,

If your're machining this your self,,practice on a junk piece,,

Some of this stuff is hard ,,,,,,Cheers,,Ben

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Thanks for the responses. I think I'm just going to let the Amish cast the parts. Other AACA members have given me some good recommendations on whom to use and the price is very low. I'll get a couple extra made in case there is a problem during machining. I don't have the proper equipment so I'll have to outsource that as well.

Radius Rod. The mystery is solved, thanks Ben.

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I've attached two images that will hopefully provide some more details on the application of the bearing case.

It does not appear that there are any internal passages that cannot be drilled from the outside, in which case, why cast anything? Simply machine a copy from steel plate, round the outside to match the casting, and sandblast the outside to roughen the finish and provide the appearance of cast. This will be both the cheapest and strongest solution, especially given the thin sections in that bearing case.

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That was actually my first choice and I'm still considering it. I need to find out how much the machine work would cost. A new casting would require some machine work so it may well be cheaper to have a near identical piece machined from a steel block than to machine a cast piece. One important thing to note, however, is that the estimate to have a new bearing case cast is $20 to $30. I was pretty surprised at the low cost. If I had the equipment to do the machining then I would likely already have the pieces duplicated. :)

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There will of necessity be a machine shop near that foundry,,

Castings usually need to be finished,,,except some farm machinery,,

Ben

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Guest Bob Call

I would be concerned about the strength of an cast aluminum copy of this part. I would think that to have the same stength it would need to be larger outside diameter. I would go with having a machine shop make it of steel. May be pricey but a shop with a CNC mill should be able to easily make this part.

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Start with hi strength alloy,,6061,,or,,7075-t6,,,,are strong and machine well,,,,or a free machining steel [/w/lead ],,

Use the old machine shop,,,lest he not be there when you need his advise,,,

The car looks a little like a Metz,,,Cheers,,Ben

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Start with hi strength alloy,,6061,,or,,7075-t6,,,,are strong and machine well,,,,or a free machining steel [/w/lead ],,

Aerospace-grade aluminum alloys noted above will be stronger than cast iron. Unfortunately, they will still only have 1/3 the stiffness. That will be an issue with the thin sections of this part.

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