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DB 450r

Heat for bearing installation?

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so i was bored at work today as usual, just thinking about this weekend when i'm goin to put a crank in a little cr80. I got to thinking about this "sweating" techniqe for bearing installation (chill the bearing heat the case) My thought is yes metal expands "outward" when heated, but when metal has a hole in it for a bearing, wont the hole actualy reduce in size due to the expanding metal? just wondering what your thoughts were.

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Yeah...you could freeze the bearing and bake the cases at 350/400 degrees in an oven.

Not sure if I'd put a flaming torch to the cases, but you're on the right track.

Just freezing the bearing might shrink it enough to fall into place.

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It's a pretty cool method, and if the case has no rubber seals you're even better off because you don't have to worry about softening or deforming anything. The whole case gets slightly larger, so yes, holes get larger too.

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Correct! I work in Tool and Die and when I tap holes I use a tap that is .005 oversized. Then if the block gets hardened it expands and gets bigger but the holes actually shrink up because of the expansion. Also when pressing a pin into a block for a press fit we will freeze the pin and heat the hole and it slides right in but make sure you get it in at the right depth or it may be hard to get the pin out. :thumbsup:

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Correct! I work in Tool and Die and when I tap holes I use a tap that is .005 oversized. Then if the block gets hardened it expands and gets bigger but the holes actually shrink up because of the expansion. Also when pressing a pin into a block for a press fit we will freeze the pin and heat the hole and it slides right in but make sure you get it in at the right depth or it may be hard to get the pin out. :thumbsup:

I always pressed in bearings. I recently tried the heat/freeze method. I used a torch and a temp gun to mesure the heat consistancy and used nitrogen to freeze the bearings. It worked well and took a little longer, but I wanted to try it. In the future I will probably use both methods

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I also just did a Hinson clutch basket using this method to get the gear in. Thud! Fell right in, which was amazing considering what it took to get the gear out of the OEM basket!

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so i was bored at work today as usual, just thinking about this weekend when i'm goin to put a crank in a little cr80. I got to thinking about this "sweating" techniqe for bearing installation (chill the bearing heat the case) My thought is yes metal expands "outward" when heated, but when metal has a hole in it for a bearing, wont the hole actualy reduce in size due to the expanding metal? just wondering what your thoughts were.

You're getting kind of conflicting answers and now I'm confused. Does the hole or bore get SMALLER when heated, which is counter-productive. I've used this method too for installing a sleeve in a cylinder. I put the sleeve in the freezer and cylinder in the oven and it went "clunk" and fell into place when I dropped the sleeve in. SO.....If the hole or bore gets SMALLER, we can just freeze the bearing/sleeve and leave the mating part alone?

Or should we freeze them BOTH???

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Heat a set of cases on a hot plate/electric stovetop/etc. and drop it from a few inches onto a benchtop... all the bearings will fall right out.

Similarly, freeze your bearings and heat your cases... the bearings will drop right into place.

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Motovex you've hit the nail on the head. I wasn't askin about the method, i was just wondering if the heating is actually usefull, or should just the freezing do the job. I know its been working for everyone, but just think about this for a bit. This pic is very crude but it shows what i'm thinking. picture a block/plate of metal with a hole in it, and its being heated. Look at the arrows, ALL the metal expands. think of water freezing, even if there was a hole in the middle its still goin to "EXPAND" correct me if i'm wrong but doesnt this seem possible. (even tho this method obviously works)

ps. Like your thought on the "should we just freeze them both" In theory it works, but in practice it wouldnt.... gets ya thinking!

Untitled.jpg

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Motovex you've hit the nail on the head. I wasn't askin about the method, i was just wondering if the heating is actually usefull, or should just the freezing do the job. I know its been working for everyone, but just think about this for a bit. This pic is very crude but it shows what i'm thinking. picture a block/plate of metal with a hole in it, and its being heated. Look at the arrows, ALL the metal expands. think of water freezing, even if there was a hole in the middle its still goin to "EXPAND" correct me if i'm wrong but doesnt this seem possible. (even tho this method obviously works)

ps. Like your thought on the "should we just freeze them both" In theory it works, but in practice it wouldnt.... gets ya thinking!

Untitled.jpg

Well, that video kind of ends the discussion! The hole does not get smaller. I'm not exactly sure what n8sjh was trying to say above but the video shows it and in practice, it works!

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I can tell you from experience that the bearing bores will in fact expand, rather than shrink. The process works very nicely. One thing you will find is that if you assemble cold bearings into a hot case, the bearing may start into the bore very freely, but "grab" the bore very soon after coming in contact with it. The bearing will still drive in with much less resistance than when cold, though, and if you line the thing up just right and set them in quickly, they can drop right in sometimes. Be sure you square them up solidly in their pockets with a driver of some kind to be sure they're completely seated.

But, regarding the heat, I don't recommend exceeding 300 degrees on an aluminum case, and 275 would actually be better. A "field" technique I often use is to heat them just until spit bounces off, and no hotter.

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regarding the heat, I don't recommend exceeding 300 degrees on an aluminum case, and 275 would actually be better. A "field" technique I often use is to heat them just until spit bounces off, and no hotter.

Yeh thats why I use a temp gun to make sure not to exceed a certain temp. I heated the cases just over 200 and it worked smoothly.

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so i was bored at work today as usual, just thinking about this weekend when i'm goin to put a crank in a little cr80. I got to thinking about this "sweating" techniqe for bearing installation (chill the bearing heat the case) My thought is yes metal expands "outward" when heated, but when metal has a hole in it for a bearing, wont the hole actualy reduce in size due to the expanding metal? just wondering what your thoughts were.

No, the hole expands outward at the same rate too. That's ME101 stuff.

OTOH, the instant the cold bearing touches the metal case, it immediately comes back up to temperature. I've tried the heat/freeze method a couple of times and have never had it help.

As an added benefit, the cold bearing also gets instantly soaked by condensation, so you get to start off your new bearing with instant moisture contamination.

JayC

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I put the bearings in their boxes/bags inside a zip-lock and in the freezer the night before. I put cases in an oven, set the temp to 250, wait 20 minutes and drop the bearings in. I do as Gray suggests and use a bearing driver to hold and align the bearing. If it starts to hang, a few gentle raps sets it.

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No, the hole expands outward at the same rate too. That's ME101 stuff.

OTOH, the instant the cold bearing touches the metal case, it immediately comes back up to temperature. I've tried the heat/freeze method a couple of times and have never had it help.

As an added benefit, the cold bearing also gets instantly soaked by condensation, so you get to start off your new bearing with instant moisture contamination.

JayC

So would you agree that pressing bearings is the better method?

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Yes and no, depending on the specific situation. Pressing bearings in place is probably better provided that the part bearing the load can be supported in such a way that the pressure will not deform it. In a good many applications where this cannot be adequately accomplished, driving the bearing is a better option.

Installing bearings onto shafts is usually quite easily done with a press, which ever part is actually moved by the press. But, when pushing bearings into relatively larger diameter pockets, it's very easy to have the bearing tilt and bind in the bore, and a press will neither provide the feedback to the installer that a hammer and driver will, nor afford the installer the same ability to correct the tilt as he works. I generally always use a driver when setting bearings into a case, and usually use a press to assemble shafts into bearings and/or bores.

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I guess what I was getting at was it all depends also on the type of metal. When I take a piece of say 4140 tool steel and drill a hole then send it out and get the block hardened the hole will shrink in the block. You are changing the structure of the material. But to harden the block it gets alot hotter than just heating it to get something to fit in it. Thats why I used the oversized tap.

For a bearing or anything that I want a press fit or even if it is tight. I will heat the outside piece and freeze the part going into it. Sleeves, Bearings, Pins, ect.

I guess it is confusing on what I said the first time. Holes shrink when you get a steel block hardened which happens when the structural make up of the steel is changed. If you heat up the block for say a bearing it will expand and and then contract as it cools.

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So would you agree that pressing bearings is the better method?

Yes.

JayC

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