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Trying to fit a drive side bearing (8 ball Japanese-made KOYO 6305 C3) and can't get it to seat straight. I've heated the cases for several minutes with MAPP gas and I'm using a BGM puller. Even though the cases are stupidly hot and bearing has been frozen for several hours, I cannot seem to pull it in square. It drops in about 1/8th of the way and no matter what I've tried it doesn't pull in straight. The case is Innocent S3 and in great condition.

It's really testing my patience. Never had this issue with drive side bearing fitment before and welcome any advice.

The MB puller looks to be a better design as it looks like it would centralize bearing as it pulls, as it uses the chaincase gasket face and locates on the studs. Unfortunately, they're out of stock, shipping to the US would be killer, and no US dealers have it in stock.

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Did the case have a bearing fitted when you obtained it?

If so, apart from oxidation or if the case has been blasted, the recess for the bearing is unlikely to have 'moved' other than through distortion in the case of welding.

Whatever you do, don't be tempted to knock in the bearing via the outer! Don't be tempted to hone the bore a nat's either, unless you can prove it undersize, as it will affect the class of fit the bearing will achieve in fitted form.

Whenever I need to pull in/out a bearing, I usually just place parallels on the appropriate gasket face with any old deep groove ball bearing (the old 6305 will do) & put some M16 studding through with nuts & big washers to pull the bearing in/out. Oh! Do the Hokey Cokey..... I keep an eye on how square it is pulling in & nudge one side if appropriate, but they always pull in.

If your'professional' tool has no bearing built in (despite it's 'proffesional' cost) then you are fighting against huge frictional losses.

I use the same principle for insertion & extraction of dozens of engine mounts & have never had to resort to heat in over 40 years.....

A good friend and mentor advised me to heat the case in the oven at 120 - 150 degrees Celsius for 25 minutes as it would result in a more uniform distribution of heat. As the cases were professionally cleaned and then tumble polished with ceramic media, I didn't hesitate putting them in the oven. Even with the door ajar, 25 mins was sufficient for the bearing to drop in most of the way in and the BGM tool (which I believe is a copy of the Innocenti factory tool) pulled it in the remainder of the way with ease.

I also measured the OD of the KOYO 8-ball 6305 C3 and compared with an Italian-made SKF 7-ball 6305 C3 and there was no difference that I could measure using digital vernier calipers.

vegansydney wrote:A good friend and mentor advised me to heat the case in the oven at 120 - 150 degrees Celsius for 25 minutes as it would result in a more uniform distribution of heat. As the cases were professionally cleaned and then tumble polished with ceramic media, I didn't hesitate putting them in the oven. Even with the door ajar, 25 mins was sufficient for the bearing to drop in most of the way in and the BGM tool (which I believe is a copy of the Innocenti factory tool) pulled it in the remainder of the way with ease.

I also measured the OD of the KOYO 8-ball 6305 C3 and compared with an Italian-made SKF 7-ball 6305 C3 and there was no difference that I could measure using digital vernier calipers.

Warkton Tornado No.1 wrote:
Did the case have a bearing fitted when you obtained it?

If so, apart from oxidation or if the case has been blasted, the recess for the bearing is unlikely to have 'moved' other than through distortion in the case of welding.

The blasting of softer alloys such as aluminium based 'upsets' the surface & therefore bores tend to grow smaller & shafts grow bigger. You should have masked any bores unless you considered them the slightest bit oversize

It's a bit like knurling in a sense, but microscopic changes.

Bead (glass) blasting will be used to deliberately increase the size of an engine piston, for example, to get back to a bore clearance that has become excessive. The surface also retains oil.

Vibratory tumbling is not blasting. All bearing faces were masked. The issue was the non-uniform spread of heat

It may appear that I'm being pedantic but the fact that the bores were masked proves the process had no effect upon altering the surface finish of the bore. I'm glad that you were cautious in protecting any journal as I cannot personally find any information suggesting that the process does not have some effect. My guess is that it does, although nothing to the extent that bead blasting will & I would suggest that vibratory tumbling with ceramic media & vapour blasting are likely the best all round options to utilise.

However, the companies that exist to offer such a service will usually state that another factor that comes about, more often considered a benefit, is that:

"Tumbling provides a certain amount of stress relief"

In the instance of virtually any metal part, machined castings included, finished journals are therefore likely to be subject to some distortion.

The clever solution of heating up to a consistent temperature throughout the casing was far better than localised heating & yielded results & a surprising low temperature. Should an oven be considered as a workshop option, what with the benefits of elevating temperatures with DIY tyre changes involving one piece rims?

Anyway, one lesson that I admit to learning decades ago & bears repeating is that with any extractor that relies upon a screw for the process will be dramatically improved with the addition of a bearing/bearings to negate friction.....