Fitting Top Bevel Bearing?

[Samurai]

Hi Guys, I've finally got around to fitting and shimming the new too bevel bearing as part of my total rebuild and need some advice.

The new bearing is a very tight to get over the thicker parts of the shaft and although I've managed to persuade it over the lower portion with a little gentle tapping with a socket, I really don't like doing that, especially as I'm very likely to have to remove it once fitted to adjust the shimming.

There must be an easier way or am I missing something obvious?

The bearing didn't appear to need to be fitted a particular way round, unlike the lower bevel bearings? I've run some fine emery cloth over the mating surface and applied a little oil, as well as heat upon fitting?

Surely one shouldn't need to persuade the bearing over the thicker parts with a hammer and socket for both fitting and removal or the thing will be knackered before the shimming process is finished?

Any help greatfully received before I knacker a very expensive bearing!

[Rocla]

Hello,
If I catched what you mean, your bearing cannot enter the housing? If yes, and if it is the genuine bearing, my advice should be to warm the housing meanwhile you keep the bearing in a freezer; You take it out the frezer just at the last moment before mounting it.
Otherwise, pushing a bearing with a hammer requires something which feets the external diameter of this bearing but with a hole inside that avoid you to push on the mobile part of the bearing

[Rick]

The best way to do it is with a cone shaped inner race heater:

bearing cone heater.jpg

I've never seen one of these heaters in a motorcycle shop- it wouldn't be too hard to turn a little taper and put it and the bearing on a hot plate to heat the inner race. A bearing rep once told me that a sealed bearing could be safely heated to 250 degrees, so an open bearing could probably be heated more than that- I'd warm it up slowly and see what it took to get a sliding fit.
Removing and replacing the bearing to get the shims right would be a problem. Do you have the old bearing? You could grind or lap the bore to be an easy fit on the shaft- use it to establish the correct shim pack, and only press the new bearing on once- hopefully.
Rick

[Samurai]

Hi Rocia,

Thanks for the reply and I fully agree with your suggestions for fitting normal bearings into housing in the crankcase and elsewhere.

However, my problem is fitting the top bevel bearing in the drive tower, that links with the camshaft bevel gear.

The issue I've got is the very tight interference fit over the upper drive shaft itself. The shaft is 'waisted' in the middle, but the upper and lower ends are thicker e.g. the same 15mm as the internal diameter of the bearing. It is at these points that I am having difficulty in sliding the shaft through the bearing.

[double diamond]

You should be using a hydraulic press or an arbor press to install and remove the bearing. Using a press will keep the bearing square with the shaft when you press it in place. The earing will install/remove easily when pressed in place. Bearings easily cock relative to the housing or shaft when hammered home. You’re dealing with a self-aligning bearing in this location. These bearings are delicate and should be treated accordingly.

The last time I shimmed a bevel shaft it took several shim adjustments to get it right, so you can anticipate removing/installing the bearing a number of times. A press is just another essential tool if you wish to work on these engines.

Matt

[Samurai]

Rick/Matt,

Many thanks for the advice and suggestions. I'll look into the hydraulic presses, though I think I'd find it hard to justify the expense for something I'd use so rarely.

Maybe I'll have to take it to an engineering shop to install it initially, although that will be a faff when I find out I've got to remove it again to adjust the shimming.

Perhaps I can adapt a normal gear puller with something to spread the load over the inner and outer races? I'll give it some more thought.

[Jordan]

Perhaps I can adapt a normal gear puller with something to spread the load over the inner and outer races?

I don't think it's possible, when removing the bearing, to access the inner race in order to push on it as well as the outer race.
That would be nice, but usually these seem to come off OK anyway. But, yours is particularly tight...

The factory workshop manual seems to assume that a shim only needs to be at the bottom, between bearing and circlip.
With luck, maybe you have all the standard parts, and can get away with not having to remove the bearing again.

I used to work at an engineering company, where there was an old guy who believed in tight fits for bearings. There was also a young bloke who preferred to linish shafts for a sliding fit. There was an opportunity to compare results, and the sliding fit machine's bearings lasted longer in service.

I was amused to overhear someone ask the old guy one time, how tight to do up a really big nut. He said to tighten it until you could see water coming out of its pores.

[Samurai]

Hi Jordan,

Interesting about the sliding fit on the shaft and the longevity of the bearing, makes sense to me. I may try easing the shaft with a little more rubbling with the emery cloth.

I've replaced the same shims that were previously directly under the bevel gear when fitting this new bearing (there was a single one under the bearing above the circlip). Hopefully the new bearing will be close to the width of the original and I'll be in the right ballpark. That's if it were shimmed correctly in the first place!

I'm going to fabricate something to enable me to press the new bearing over the thicker section at the upper and of the shaft, to save any more stress on it. Let's hope the last guy to shim it knew what he was doing or else that the bearing fit eases up in the process if I have to remove it again

[Samurai]

Ok, just to update and close this thread. I had a word with both Brian Silver (Moto Marianna) and Nigel Lacey (Lacey Ducati), both of whom were most generous with their time and advice.

Basically the issue is now resolved, I just needed more patience with carefully easing the diameter of the bottom of the upper bevel shaft!

In the end it took me about another 30 mins carefully turning the shaft in a vice and using 800 grit wet and dry paper (Emery cloth). The end result is a bearing that is a snug but sliding fit over the shaft

Interestingly, Nigel then discussed how he would normally get around the issue of ensuring the correct gasket thickness so that the bearing carrier does not spin in the head. Throw it away and use a gasket forming sealer, as he has done for the last 25 years without any issues!

The theory being that gaskets are all fine and dandy when the components were new and perfectly machined, but many will have become warped and butchered over the years.

Together with the fact that over a sheet of gasket material, the thickness will inevitably very a little and this method saves a lot of messing about.