How hot?

Onder · Jan 9, 2015

How hot can I go in heating a crankcase in an oven to release a bearing?
Usually 250 F and the bearing will drop out.
What is the upper limit of heat. I dont want to remove a bearing and weaken
the case.
Is it better to heat the whole case or better to use local heat ( torch or heat gun)?

Rohan · Jan 9, 2015

Which bearing are we talking about ?
And how assembled is it ?
Are you plunking it down on the recommended bit of 4 x 2, to jar the bearing loose ?

The traditional test - for releasing bearings by heating the alloy case - is to spit on the heated area, and it 'should spit back'.
This is surprisingly hot, when water droplets will dance on the hot alloy.

Be careful of locally heating things with a torch - especially an oxy torch, a propane torch is safer.
If you get it locally hot with an oxy torch, its not impossible to melt it !!
Alloy has the charming property that it doesn't show heat, it simply slumps and flows away...

ashman · Jan 9, 2015

I usauly put the case over the stove flame and heat it that way usauly only takes a few minets and the bearing will drop out then I turn it over and drop the new one in, I have done it this way on many Norton cases and works faster than the oven.

Ashley

Onder · Jan 9, 2015

The oven provides even heat or so it would seem .
I can weld and you are so right about alloy turning to nothing if you get too loose with the torch.
Im just looking for someone to give me an actual figure. The oven is close and I have a
infrared thermometer.
So can anyone tell me what the upper safe limit would be? Can I got to 400 or is that
looking for trouble?

Hobot · Jan 9, 2015

for pre-peel with distorted cases and a bearing hang up cockeye'd I got into oil smoking frying pan hot upper 400'sF no problemo. I don't mess around and always go straight over 300'f now and it that don't do right away then back on til it does. I do this in minutes with a pancake tank top propane heater. If frying pan oil smoke heat hurts your cases then way better you find out at home than later. If really jammed in the coolest way is weld an electric stick on race, wait 30 sec for heat expansion to move outward and race shrinks then lift out like a lolly pop. Only thing oil vaporizing heating should do is clean the pours so finish less dark and destress the metal grains if cooled slowly. I got Peels to oil burning hot and beyond all over with the detached space heater on a hose for her case re-enforcements. Still giggle at the welder after getting out his biggest acyl/O2 torch and til I lit mine off which made it look like a candle so he nodded and switched tools and got to work heating way way more the surrounds being melted sickingly to me. Hehe is 250 too much, not if ya burp your tender baby soon after.

Mark · Jan 9, 2015

How hot? I honestly don't know, but.......
I use my heat gun a lot. It goes to 750 degrees, and I run it wide open.
I blast the aluminum good enough that any oil residue is left smoking and it is too hot to touch.

Then I leave it set for a few minutes before trying to get the bearing race to release.
If I had to guess, I'd say that the 350 range is enough to start things moving.
I like the heat gun (or torch) as opposed to an oven because the heat can be directed where needed - around the bearing / in the aluminum.

......Now I am curious as to the temp that the cases start to expand (constrict?) and bearings start spinning in their bores.
I bet comnoz knows.

Hobot · Jan 9, 2015

Cooking and engine oils have similar vaporizing flash to smoke temps so i use basic chef's methods to ballpark temp.
Its does take some time to fully expand like yelling fire in packed room and the thicker the piece the longer to wait. cases seem to take a couple min. Loose bores may drop race out at room temp so sliding scale the manual ballparks expected temps. I tell ya what last thing ya want to skimp on heating is replacing a good tight fitting bearing that takes a bit to get aligned just right and it begins to swell while the bore contracts and allows just enough insertion before the micro angle of mis alignment jams it cocked most the way in, ugh. Space age has laser remote temp sensors solve mystery and eventually will just have our pet robot doing it, then test ride its handy work. Heat guns hair dryers are one the most multi purpose tools I own, though rare to use still figuring out or seeing new uses with no end in sight.

comnoz · Jan 9, 2015

The general rule with that type of alloy is you would be safe with 375 F. for periods less than 1 hour.

300 F. is safe forever.

I set my oven at 350 F. for bearings. Jim

mschmitz57 · Jan 9, 2015

I stuck my impeccably clean case upside down in the oven on the top rack with a cookie sheet under it to catch the bearing.
It dropped out fairly quickly during the warm-up phase. Klunk!
I bet it didn't reach 200 yet but 250-300 sounds about right.

gjr · Jan 10, 2015

When the oil stinks/smokes, it is ready.

Greg

acotrel · Jan 10, 2015

The usual solution heat treatment for aging aluminium alloys is to soak castings in a 100 deg. C oven over a fairly long period of time. To soften aluminium you need to heat it over 500 deg. C. I use the Rohan and Ashman method to replace bearings. Heat the crankcase half inverted over a medium sized jet on the gas stove, and spit on the outside of the case now and then until the spit fries, then tap the edge of the case on the wooden bench. If you walk away and leave the casting over the jet, you might burn the aluminium however you'd have to be very careless.

PeterJoe · Jan 10, 2015

I have learned from a BSA Motorcycle mechanic many years ago that all they used is an inexpensive electric cooking hot plate (K-Mart, WalMart, etc). Just support the case above the heating element and in not too terribly long of a time a bearing will fall out. Sometimes tapping the case with a mallet will help shake the bearing free once the case is hot. I have had very good success with this method.

comnoz · Jan 10, 2015

acotrel said:
The usual solution heat treatment for aging aluminium alloys is to soak castings in a 100 deg. C oven over a fairly long period of time. To soften aluminium you need to heat it over 500 deg. C. I use the Rohan and Ashman method to replace bearings. Heat the crankcase half inverted over a medium sized jet on the gas stove, and spit on the outside of the case now and then until the spit fries, then tap the edge of the case on the wooden bench. If you walk away and leave the casting over the jet, you might burn the aluminium however you'd have to be very careless.

To completely anneal aluminum would be heating to 500 C /930 F. and then quenching in saline solution. this would render a case useless and change the dimensions.

Softening of previously heat treated A356 alloy starts at around 400 F. / 200 C. Below 500 F / 260 C. the damage is minor.

That is why Norton heads slowly get softer and the distance between the bolts holes increases as the miles increase.

RoadScholar · Jan 10, 2015

350.

Preheat the oven, add the case, go have a beer, if your environment is quiet enough you'll hear the race drop.

If the replacement is cooled and is available, drop it right in then worry about something else.

Bill.

john robert bould · Jan 10, 2015

Dont bother heating up the case!!! I haven't spent years in engineering not to know the proper way to remove outer races...no case heating required... :roll:

Fast Eddie · Jan 10, 2015

john robert bould said:
Dont bother heating up the case!!! I haven't spent years in engineering not to know the proper way to remove outer races...no case heating required... :roll:

You gonna educate the rest of us then John...?

john robert bould · Jan 10, 2015

Eddie... this is the trick.
You need a stick welder , use a 2mm rod and weld the inner bearing surface , use a hands free mask and as the weld applies turn the case/bearing to put a run on the track face..two or three turns may be required to complete the weld circle ...this will shrink the race upto .006/8 thou and the bearing drops out on its own,
Used this to remove many outer races, the case only get's warmish..i was shown this 30 years ago..works like a dream every time..first used it on velo's to remove the taper main outer race's.
Anyone who doe's it will never go back to "case heating"
ERF king pin taper rollers are almost impossible to get out, the welding trick removes them while having a brew

Fast Eddie · Jan 10, 2015

I'm aware of that trick actually John, although I've never done it.

So, after doing this, how does one fit the new bearings, bash 'em in cold with a big mallet?

It's probably what the factory did after all (Triumph did)!

john robert bould · Jan 10, 2015

Nar freeze the bearing! the idea to remove the bearing prevents damage in a lot of case's ie vellocetts , the time i have seen chisel/wedge cuts in the bore face, any way the original question was how hot to get the case ..my answer is No need,,,refit is another question. Big mallets are for wood work :lol:

Fast Eddie said:
I'm aware of that trick actually John, although I've never done it.

So, after doing this, how does one fit the new bearings, bash 'em in cold with a big mallet?

It's probably what the factory did after all (Triumph did)!

comnoz · Jan 10, 2015

john robert bould said:
Eddie... this is the trick.
You need a stick welder , use a 2mm rod and weld the inner bearing surface , use a hands free mask and as the weld applies turn the case/bearing to put a run on the track face..two or three turns may be required to complete the weld circle ...this will shrink the race upto .006/8 thou and the bearing drops out on its own,
Used this to remove many outer races, the case only get's warmish..i was shown this 30 years ago..works like a dream every time..first used it on velo's to remove the taper main outer race's.
Anyone who doe's it will never go back to "case heating"
ERF king pin taper rollers are almost impossible to get out, the welding trick removes them while having a brew

I use that method to remove valve seats all the time -but main bearings -no. Jim

How hot?

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