Bultaco Sherpa main bearing fitting on rebuild.

[chappo]

Just wondering what methods people use out there to fit the three main bearings, we're all individuals and have our thoughts and methods.

Ive rebuilt a 198a last year and rebuilt the engine and just thought before i do this one I'll canvas opinion just in case someone has a better or easier way of doing them. Is it crank in freezer then drop hot bearings onto that or bearings in the cases and then frozen crank in that way. The outer bearing on the primary side , same question.

How do you heat the bearings, hot oil or other method?.

Going to do my 199b in the next week or so.

Just asking before I start.

 

Thanks guys.

 

[2stroke4stroke]

My Bultaco rebuild days are ancient history now but I used a guide from one of the weekly papers that had been written by some guy name of Miller; I believe he rode a Bultaco.  Drift mains in to heated casings then tap crankshaft in to place.

Nobody had a domestic freezer then so the question did not arise.

Edited April 18, 2017 by 2stroke4stroke

[netley]

Cases in the oven and bearings/crank in freezer

[dadof2]

Many years ago on my first bulto rebuild using the method above (recommended in a manual) I ended up with burnt fingers and the job jammed before the crankcases were fully closed. The following method is more reliable and far less likely to damage the bearings.

First fit the bearings into the crank cases by warming the cases and cooling the bearings, if any pressing is needed press on the outer race only. 

Next ensure the crank surfaces where the bearings will fit are really clean / well polished. From memory install the crank into the left hand case first. Do this using a selection of tubes of slightly different lengths, that are the same OD and slightly greater ID than the inner race of the bearing. Using the flywheel nut gradually draw the crank into the bearing. Cease when the crank is about 1 mm from fully seated. Fit the RHS case using the same method. When there is a gap of 1 to 2 mm between the cases keep checking that the flywheels are central in the cases. Gradually tighten alternative sides until the cases close, keeping checking the crank is central and tightening whichever side as appropriate.

When fitting any bearing the important thing it to apply the insertion pressure so hat it is not transmitted by the balls / races.

Edit - I use an electric hotplate to heat the bearings. It has adjustable temperature and only cost a few £ from Argos I think. My wife bought it to use in the garage cos she got fed up with oily bearings on her cooker.

 

Edited April 18, 2017 by dadof2

[spen]

We use one of these, there's a trip switch on the base to cut the power if it topples over, a bit of duct tape over the switch to hold it in place, lay the heater on it's side and stick anything you want to warm up on the grid. Switch the oscillating facility off first... ;>)

 

http://www.ebay.co.uk/itm/Brand-New-1200w-Oscillating-Halogen-Heater-/222457174334?_trksid=p2385738.m2548.l4275

Edited April 18, 2017 by spen

[71zman]

An American method to apply heat is to use "the Weber" - a gas BBQ that you cook your steaks on. I heat the BBQ to around 500 F, put the cases in and let them soak about 10 minutes - I use a low cost non-contact infrared thermometer to measure the case temp - when they get to 400F they are ready for assembly. The advantage of this method is the wife doesn't get mad about messing up the oven in the kitchen although I must admit my steaks have hint of Castrol seasoning on them.......

Also - I prefer to put the bearings in the case first as described above by dadof2  - nice description.

Edited April 18, 2017 by 71zman

[bondy]

Hot Air gun that's all you Need no freezer if you already rebuilt a 198A then you will have no problem with the B the main bearings are just the same as the 198A I know many have there own method off doing the bearings.

[pschrauber]

I don't like to hassle around with heated parts and get burned by them, I recently got burned a lot while trying to replace roller bearings to a swing arm...

 

So now using ice spray to cool down the bearings and gentle heat with an hot air gun. This combination works very well:

- first heat up the parts where the bearings belong,
- then a spray to the bearings to cool them down,
- and finally let them drop in et celá.

[chappo]

Thanks for the all the views guys, getting it put back together this week..

 

[chappo]

I've tried both methods now, bearings on the crank then crank into hot casings, also bearings into casings and then crank into bearings.

Found the later method easier, heat the casings, bearings have been in the freezer, just drop them in.

Heat the bearingswith a heat gun, have the crank in the freezer overnight, just drop it in.

Thanks guys.

[guys]

When you put the bearings in the casings first, they sit at the outer most location in the casings.

If you then mount the crankshaft, the bearings wont be seated properly on the crankshaft (all the way against the counterweight), leaving no room for axial expansion when the engine heats up.

[chappo]

Thanks Guys, why didn't you post earlier ??

I suppose that makes sense, but I put the crank seal holders in both sides first so the bearings fell to the correct point and the bearings on the inside were flush to the crankcases.

When I dropped the crank into the cases, with bearing already heated, ( the crank had already been in the freezer ) it dropped in with a beautiful thud as though it had mated with the crank counterweight.

The gap on both sides of the crank to casing were almost the same when measured.

It also sounds very well now it's running. 

Im happy at present,  subject to any axial movement.