<-=- Club Bevel Heaven -=->

Hi, Evening All,

I'm looking for some advice on fitting new taper roller head bearings on my 1979 900 Replica (MHR) number 146.

I have had a tool made which slips over the stem of the steering base and has a machined end profile to be able to drift the inner race of the taper roller bearings down into place.

So, by my reckoning, they need to slot over the top of the stem, and be drifted across the first machined face where the top set of bearings fit and then drop down the stem to the second and lower machined face of the base and drift into place.

So, question, I have a mechanical device to drift them into place but:

1 - Should I chill the base in the freezer for an hour or so to contract the metal and and allow the taper roller race to drift easier across the top machined face.

2 - Should I heat up the inner roller race to allow it to expand and drop over the stem easier and locate on the bottom machined face.

3 - Should I do both, freeze the base/stem and heat the roller.

4 - Should I do neither and just gently drift it cold.

5 - Something else I haven't thought of?

Be grateful for any assistance.

Stuart

Hi,
I did this recently on my 900ss, most people just slip a bit of tube over the steering stem and drift the inner race into position. If you want to be extra careful then do exactly as you suggest, stick the stem in the freezer and heat up the race, then it will just fall on with a satisfying clunk. Don't overheat the race because of hardening issues, boiling water should be enough and is easy, up to 200 C in the oven should be fine unless your wife kills you...
The same technique (just freezing the outer races) works with fitting them in the frame, if you want to be extra fussy then a piece of 10mm studding (threaded bar) or a suitable long bolt down the headstock, two big (bigger than the races) washers/plates and a couple of nuts will neatly push the races in as you tighten the nuts, but not really worth the faff, a bit of wood (as Steve suggests) and a stumpy sledge hammer will make them leap in!
Good luck!

Like wot in-two said, Stuart ...

1. Hot + cold: Yes (IMO, always with bearings and interference fits, on the grounds of, 'Why Not?')
2. Draw bolts: Yes, if you want to have a bit more control than ...
3. Wood and hammer: Yes, if you don't want to faff about with (2). Just don't hit things too hard (races can be easily bashed out of shape)

Thanks for the advice chaps - will get to it this week and keep you posted,

I like the idea of freezing the outer races and using a draw bolt - much more polite as an insertion method.

Cheers

Stuart

Stuart,Craig et al.
I'm at an age where polite and controlled insertion methods are my only options...

I am also fitting new head bearings on my 73 Sport and will use the hot/cold method. We often use a heat lamp for the inner races. I did notice a fair amount of paint overspray in the bore of the steering head so I cleaned that up a bit. I then noticed that the bore is out-of-round by about .07mm (.003") and wondered if the paint may have served a purpose.
Fred in Ohio

jakebrake wrote:I then noticed that the bore is out-of-round by about .07mm (.003") and wondered if the paint may have served a purpose.

Hi Fred,

Ah ... a 'feature' much noticed in Laverdas, but not one that I have often (ever?) seen discussed with regard to Ducatis. Which is kinda weird, given that Verlicchi made the frames for both marques ... Anyways:

In "Laverda World" there are three fixes (for those who like things to be right ):

1. Grind the housing to make it nice and round before fitting the specified size of bearing.

2. Ease the outside race of a standard bearing just where it pinches - see description below.

3. Fit a bearing with an undersize outer race, but glue it in place using a bearing adhesive.

Here's a posting from someone who know his stuff (Steve Battison):

"The undersize bearing outers are to allow for the ovality of the headstock tube inherent in any welded tube not remachined after welding (which is too difficult/expensive for mass production). Measuring the typical headstock bore will show you around about 0.2mm of ovality. When a light interference bearing race is installed, theory says it flexes somewhat to match the headstock ovality, hence the rollers touch the race only in places.

What I do is use a normal bearing, measure the diameter of the bearing bore where it's "pinched", then hand grind opposing sides of the bearing outer to suit, usually down to around 51.8-51.9. Takes a bit of fiddling, but it's surprising how effectively this can be done on a normal bench grinder. The bearing should remain a slight interference fit. Clean everything with acetone or similar and then mount using Loctite 609. I cool the race and heat the headstock, then carefully hammer in using a slightly undersize drift.

I can't say for sure whether it makes a noticable difference, but often bikes put together using lots of little tricks like this just "feel" better than another seemingly identical bike. On an engineering level, it makes sense not to force a round thingy into an oval whatsie when the objective is to have the resulting thingy/whatsie still round."

Ciao

Craig

Well I assembled my triple clamp, steering head bearings and forks this evening - all went smoothly and that's a pile more new and shiny restored bits added to the bike...looking good.

8 mins at 160 degrees and the inner race dropped nicely onto the bottom of the stem with just a little gentle persuasion from the special tool I had made.

Thanks to everyone for their advice, support and help.


Job done.

Wheels in this weekend and she should really begin to look like a bike.....can't wait.... is in sight now....

Stuart

Congrats Blacklightning, its great when a pile of bits starts to resemble a motorcycle.
A quick comment on Craig's/Steve Battison's technique, great to find someone doing things 'properly' , I don't bother with road bikes, particularly old ones, but stuff for the track is another story. I usually use an old school bearing scraper for getting paint/weld spatter/rust out of the headstock bearing recess and it is very effective for getting them round again, particularly with alloy frames. In a hurry or working with a frame with the engine in so not easily inverted, a die grinder with an abrasive flap wheel is quick but the potential for a balls up is high.
Grinding down the outer races sound easier and very effective but was 'against the rules' in our race shop, we always had to correct the error rather than mod the correct part, just for repeatability, new head races for every event in endurance racing...
Happy scraping!

And of course you all know that the rear wheel bearings designed for the good old Fiat 500 are the same as the head bearings of our twins...??
And that bearing is plenty available at low prices everywhere...!
SKF VKBA 562

VKBA-562 is NOT the correct sized bearing.....

the correct sized steering bearing is 26 x 52 x 15

The VKBA-562 is 26 x 52 x 14.26 So, you end up with 1.5mm shorter stack assuming you replace both bearings.