Bearing temps frustration.

[husqORbust]

I reckon chilling the bearing has more to do with the time it takes to expand, rather than how much it shrinks.

Take a .003" heat shrink fit for example.

Chill bearing from 2.0000" to 1.9998"
Bearing is 2.0000" at room temp. Bearing expands to say..... 2.0010" at some temp between room and an expanded bores temp
Bore is 1.9970"
Apply heat to bore, it expands to 2.0010"
Now its a .0010" slip fit.
If it took 2x as long to go from -20°C to expanded temp than it took from room temp, you would have boughten yourself 2x the time to seat your bearing in a very small window of opportunity where there is a .001" slip fit. Knowing that, freeze your bearing, heat the case up, put it together square, and have something to hammer it within a split second if it hangs up.

In the best practices, a piece of dust will damn near hang up a .001" slip fit...so having .5 of a second extra to drop something in the hole is major.

Or, skip the freezing process, and properly heat the case up. In any event, I think if the bore isnt HOT enough, you'll have problems.

Totally arbitrary numbers. Just trying to illustrate my thoughts on what freezing will actually do with a heat shrink fit up.

 

[MagraAdam]

I don't understand why people are so passionate about freezing the bearings in a home freezer. I agree that something like liquid nitrogen or CO2 will get it cold enough to make a difference, but I think Tom proved well enough that when using a home freezer it doesn't take it low enough to mean that you can heat the case any less. So if you're going to heat the case to the same point, why wait the hours for what in practicality is no difference? If you've got a way to go colder than a house hold freezer (which should be about -14c minimum) then go nuts. But if not, why turn a 1 day job into a 2 day job?

I mean, everyone is free to do whatever they want, but don't we all come here to get advice on how to do things better? Didn't you read this thread to see what the answer was?

As someone relatively new to this side of working on engines, I'll be investing in an IR thermometer and skip the freezer and manage the heat correctly.

 

[sean donato]

Just a thought, hes using a regular freezer, which typically wouldn't go bellow 0*f. Most deep freeze will start at a a minimum of 0*f and down into negatives, my deep freeze at the house is set for -10*f with the capability of being set to a lower temp. It's all proportionate to the temperature difference and what you have available to you to make that temp differential as far away as possible.

 

[Cantdog]

I don't understand why people are so passionate about freezing the bearings in a home freezer. I agree that something like liquid nitrogen or CO2 will get it cold enough to make a difference, but I think Tom proved well enough that when using a home freezer it doesn't take it low enough to mean that you can heat the case any less. So if you're going to heat the case to the same point, why wait the hours for what in practicality is no difference? If you've got a way to go colder than a house hold freezer (which should be about -14c minimum) then go nuts. But if not, why turn a 1 day job into a 2 day job?

I mean, everyone is free to do whatever they want, but don't we all come here to get advice on how to do things better? Didn't you read this thread to see what the answer was?

As someone relatively new to this side of working on engines, I'll be investing in an IR thermometer and skip the freezer and manage the heat correctly.

I concur.......If you have dry ice or similar then go for it but the temp differential gained from room temp to what a common food freezer cools to is not worth the effort....nor the hassle. You still have to heat the cases so you might as well heat them enough to get the job done.....that way you only have one part of the equation trying to get back to room temp while you work rather than two.

 

[Canyon Angler]

I have access to liquid nitrogen. I cool the bearing with it and heat the case with a trip to the oven until 200 degrees.

I think using an oven is gonna make the biggest difference as far as expanding the case goes, much better than heating it on a gas stove flame, because a heat soak in the oven is gonna bring the whole casting up to 200° ... whereas if you just heat the area where the bearing goes over a gas flame, the rest of the casting, which will probably be at a lower temperature, is going to chill the area that you just heated.

Whatever the case, Tom showed that it worked just fine with just a gas stove, so I guess it's a moot point. But if you were concerned about not getting the case too hot, the best solution would be to bring the whole casting up to whatever temperature you figure you needed at a minimum, then scramble to get your bearing seated.

 

[Vintage Engine Repairs]

I think using an oven is gonna make the biggest difference as far as expanding the case goes, much better than heating it on a gas stove flame, because a heat soak in the oven is gonna bring the whole casting up to 200° ... whereas if you just heat the area where the bearing goes over a gas flame, the rest of the casting, which will probably be at a lower temperature, is going to chill the area that you just heated.

Whatever the case, Tom showed that it worked just fine with just a gas stove, so I guess it's a moot point. But if you were concerned about not getting the case too hot, the best solution would be to bring the whole casting up to whatever temperature you figure you needed at a minimum, then scramble to get your bearing seated.

The oven is such a good way to get a great consistent heat, the downside i found is the slow long heat soak of the cases, essentially, yellows the paint. Check this out - it was the reason I stopped using the oven. A 30 second high heat like a blow torch right on the pocket doesn’t affect the paint. Seems that powdercoat has a resistance to heat for a period of time before it succumbs and yellows

Needless to say you can see what has and what hasn’t been out in an oven - no more oven for me

now you have me thinking though, instead of bringing the cases up to say 375f in an oven, if you just put them in from room temp straight into 375 for a minute or two would that work? How long would it take to get the cases to the right temp? I haven’t tried that

It takes my oven about 15 mins of heating up before getting to 375f thats a lot of time that the powdercoat is exposed to high heat.

 

[sean donato]

Idk if powdercoat will be affected by the heat so much, as it's a heat cured coating. Regular paint yeah even with a torch if your not careful will discolor pretty quickly.

 

[kybob]

Another major factor in all this is the held bearing fit dimensions. Even bearing sizes can vary a few tenths


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[Canyon Angler]

If you're concerned about elevated-temperature aging of the paint, Tom, maybe the thing to do would be to preheat your oven to its max temperature (say 500°F) before putting your casting into the oven, then monitoring the casting temperature with an IR thermometer, and as soon as it reaches the minimum temperature you need (if I recall right, you said 120°C or 248°F), then take it out and install your bearing. That way, you'd bring it up to temp as fast as possible (it shouldn't take long -- aluminum soaks up heat FAST), and the whole thing would be hot, so it shouldn't cool down as fast as it would if only part of the casting were 248°F and the rest of it was 100°F...just another idea.

 

[Bob Hedgecutter]

The way I see it, if a saw has done an honest lifetimes work to the point of it needing new crank bearings- the finish of the case halves is going to be showing a lot of honour badges on the original cosmetic finish and be somewhat patinaed, if you overheat and discolour the original finish, no real harm done.
If however you have sanded, bogged up and painted the case halves with rattle can spray before bearing application, perhaps you want to rethink your order of assembly and paint after bearing installation.
I don't really care who puts bearing in how, they are your tools, do what you see fit, however- I will add that perhaps a cold bearing (household freezer cold) may absorb heat a little slower than a room temperature bearing. According to most Stihl manuals, cases should be heated to 120 deg C or 250 deg F and the (new) bearing should "drop" into the case- but this operation MUST be performed quickly as the bearing shell will rapidly absorb heat from the case and expand.

 

[Mad Professor]

The oven is such a good way to get a great consistent heat, the downside i found is the slow long heat soak of the cases, essentially, yellows the paint. Check this out - it was the reason I stopped using the oven. A 30 second high heat like a blow torch right on the pocket doesn’t affect the paint. Seems that powdercoat has a resistance to heat for a period of time before it succumbs and yellows

Needless to say you can see what has and what hasn’t been out in an oven - no more oven for meView attachment 914184View attachment 914185

now you have me thinking though, instead of bringing the cases up to say 375f in an oven, if you just put them in from room temp straight into 375 for a minute or two would that work? How long would it take to get the cases to the right temp? I haven’t tried that

It takes my oven about 15 mins of heating up before getting to 375f thats a lot of time that the powdercoat is exposed to high heat.

Hows the wife/gf like chainsaws in the oven?

 

[Madmantrapper]

I usually boil the receptor in water if possible and put the bearing in the freezer. When putting bearing on shaft I usually put the shaft in the freezer and boil the bearing, has always worked for me. Large bearing for power presses, I used to heat in oil using a rosebud. One day the oil ignited, that's a story for a different day.

 

[Vintage Engine Repairs]

Hows the wife/gf like chainsaws in the oven?

She’s not overly happy but also, they are always clean so she doesn’t mind too much