Heating main bearings to drop crankshaft in?

Is it bad to directly heat the main bearings with a blowtorch?

Yes!!!!!

 

Try putting them in a oven. Bearings bust be heated at 80ºC maximum.

Using an oven is the best way because the temperature can be more accurately controlled and limited. Bear in mind it will take 20 minutes at temp to uniformly heat the part.  275 ℉ (135 ℃) is the temperature GM recommends for this sort of work, and I haven't had any trouble working at 250-275 ℉.  80 ℃ is 176 ℉, and that may be only marginally helpful.

 

You can use a torch, however.  It doesn't give as good a result, and it is potentially dangerous, but you can mitigate that by being cautious.  There are wax temp sticks available from most supply houses that service welding and/or machinist trades.  Get one that melts at 240-260 ℉ and don't go hotter than when it melts against the inner race.  Absent a wax stick, heat just until a drop of water will bounce off the metal instead of sizzling on it. Bear in mind that the bearing cage will heat faster than the races, so avoid direct heating of the cage. 

So I can put the whole engine case in the oven with the bearings Im the case and then drop the crankshaft in?

If you've got the bearings installed in the case that generally means you're going to heat the whole case, including seals that are installed.  A torch can cook a crank seal very easily and is likely to do so before you get the bearing hot enough to make any difference.

 

Your best best is to just buy a Tusk crank installer and never have to worry about screwing up another bottom end.  Heating and dropping in a crank always sounds better in theory than it works in practice.

 

 

Heating and dropping in a crank always sounds better in theory than it works in practice.

 

I disagree with that, but you do have a good point about the seals.  If there's a seal that has to be installed under the bearing first, the torch is not an option.

 

As to the heating/dropping in working, one thing you may well run into is that the bearing may "grab" the crank part way in.  The expansion that occurs in the bearing won't amount to a lot, and the cold crank can cool the bearing enough to have it shrink onto the shaft.  Then you're faced with having to finish seating it with conventional puller/installers anyway.   To avoid it, the shaft must be inserted quickly, smoothly, and completely in the shortest possible time, and it does take a bit of practice.  I usually use heat to reduce the stresses involved with using a puller cold, and most of the time, I don't need the puller at all, but for those times when the bearing grabs hold, there isn't anything like having the right tools.

I disagree with that, but you do have a good point about the seals.  If there's a seal that has to be installed under the bearing first, the torch is not an option.

 

As to the heating/dropping in working, one thing you may well run into is that the bearing may "grab" the crank part way in.  The expansion that occurs in the bearing won't amount to a lot, and the cold crank can cool the bearing enough to have it shrink onto the shaft.  Then you're faced with having to finish seating it with conventional puller/installers anyway.   To avoid it, the shaft must be inserted quickly, smoothly, and completely in the shortest possible time, and it does take a bit of practice.  I usually use heat to reduce the stresses involved with using a puller cold, and most of the time, I don't need the puller at all, but for those times when the bearing grabs hold, there isn't anything like having the right tools.

 

That's what I'm saying.  It sounds like a good idea in theory but doesn't usually work out.  Especially in a situation like installing a crank where you are going to have to deal with not just the crank and main bearing but the transmission shaft, countershaft, shift shafts and shift rod.  Expecting to heat up the entire left side case, for example, and have it drop right on over everything else is never going to happen.

 

You might get lucky and be able to drop a bearing into a hot case but the whole motor isn't going together like that.  Better to spend a little money for the tools you need so you don't end up with a crank stuck halfway into a bearing.

Depends on how the particular engine goes together, too, but in any case where you're putting the second half of the case onto the other one, and it happens to be one that uses a sealer only in the center joint, well, you can't use heat on that one.

 

It's a good method when and where it's suitable.  It just isn't always.

It's a yz125 seals can go in after, I have done it with freezing the crank and heating the inner race of the bearing and it worked out perfect except the fact the some how the bearing got s flat spot in it. I'm not sure how that happens because everything was done with heat and went together smooth. Maybe the torch heating directly on the bearing messed it up. I'm not sure just wondering if there's any other ways of using heat. Thanks for all the replays guys!!

If your cases require sealant between them heating a case half in the oven is going to cause that sealant to set up too quickly. You can heat up a socket or something similar to transer heat to the inner race. Look up "heated slug" or the Ken Oconner videos.

Also make sure you were using quality bearings, not the ones that come in an AllBalls kit.

Edited by TimTee

If your in the Cincinnati,Ohio area will will let you use my tusk puller!!

That's what I'm saying. It sounds like a good idea in theory but doesn't usually work out. Especially in a situation like installing a crank where you are going to have to deal with not just the crank and main bearing but the transmission shaft, countershaft, shift shafts and shift rod. Expecting to heat up the entire left side case, for example, and have it drop right on over everything else is never going to happen.

You might get lucky and be able to drop a bearing into a hot case but the whole motor isn't going together like that. Better to spend a little money for the tools you need so you don't end up with a crank stuck halfway into a bearing.

truth!

you may get Lucky a few times with heated slugs but all it takes is once and you get to pull it apart in a not fun way if the shift shaft gets miss aligned.

Heat up an old socket the size of the inner race with a torch. Set it on the inner race for a minute. Remove and assemble.  Works like a charm.

Sorry Timtee. Didn't see your post.

Edited by blackie107

Heat up an old socket the size of the inner race with a torch. Set it on the inner race for a minute. Remove and assemble.  Works like a charm.

 

+1 this method along with Buzzetti crank installation/puller tool to center the crank works for me too  :thumbsup:

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