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Question for the masses re Ceriani front axle assembly:

2203 Views 16 Replies 3 Participants Last post by NortonComm, Feb 7, 2020

NortonComm

Discussion Starter · Feb 3, 2020

I have a new to me 1978 Ducati GTS with Ceriani front forks. (The bike came mostly in boxes of bits so I don't know what 'correct' looks like in all cases.) I am installing the front axle. When I put the assembly together- from right to left side- the axle slides through a stainless spacer washer, the speedo drive assembly, the axle carrier tube, then the large spacer on the left side, then the washer and axle nut protruding through the left fork stanchion. It all goes together fine, and the brake rotors are where they should be, but if I tighten the axle nut beyond a certain point, it seems that the tapered bearings bind and the front wheel no longer turns freely. That can't be right. It seems like there is nothing stopping the axle from being drawn through the wheel frm right to left by the force of the nut compressing. I can't find a Ceriani axle assembly diagram anywhere to check my homework. Am I missing a part? A washer? Any ideas? ( I have backed the axle nut off slightly until the front wheeel turns freely again, locked the axle in place with the pinch bolts, and ridden the bike- it rides fine with no strange front end wobble, but I still can't believe it's meant to be this way.....)

Thanks for any insights.

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NortonComm

Discussion Starter · #4 · Feb 3, 2020

Duccout; thank you very much.

First thing- having now disassembled the interior wheel components, I see you are right. Ball races, NOT tapered roller bearings. So that eliminates the idea of the bearings races being compressed and binding.

Second, I took off the rotors ( not the calipers) and reassembled the whole front end. Everything seemed fine, with no friction and no binding.

So then I put the rotors back on, and reassembled the entire thing. I used the tightening sequence of right pinch bolt, axle nut, left pinch bolt, etc etc ( from posting to this web site 3 years ago). Everything is tight and aligned, and there is no more binding. The wheel rotates as it should. the axle can't drift because of the pinch bolts, and because of the washer and big lock nut at the end. I don't know what I did, but disassembly and careful reassembly seems to have solved the problem.

So my question is less critical because it seems like all is in order now, but I still get the feeling that if I tighten the axle lock nut more it will have the effect of drawing the stanchion tubes together and creating the binding problem I had before. I have old BMWs and Nortons and a KZ900 and on none of those bikes can you do that. Just wondering if this sounds okay to you.

Thanks again for the input.

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NortonComm

Discussion Starter · #5 · Feb 3, 2020

rick81mhr900ss said:
I think you may have a washer issue between the speedo drive and the right side fork; they are usually made of aluminium and stainless is an upgrade. The ally ones can dish. The combined thickness of the speedo drive and washer must equal the thickness of the spacer on the other side for the wheel to be centered, assuming that the wheel bearings are pressed in equally on both sides. On my 81 MHR, when all is tightened up, the centre line of the brake discs is exactly centered with the center line of the brake calipers on each side; an easy thing to check.

How tight is the fit of the axle carrier tube (front wheel bush) between the two bearings? It should be tight; a pain in the behind sometimes trying to get the shaft in when the bush shifts slightly. If it is loose, then your wheel tightness on tightening my be due to inward pressure on the bearings because they are not being supported by the bush in between them.

Interesting thoughts. See the note to Duccout I just posted. I'll answer the question you raised in order.

1. I replaced the old washer on the right side with a new, recommended stainless one.

2. As near as I can measure, yes, the wsher and speedo drive combined measure the same as the fat spacer on the left side.

3. I'll check caliper alignment with the rotors, but they look to be where they should be and there is no dragging on either side.

4. Axle carrier tube: I dunno! It goes back in place easily and, compared to working on old Nortons and BMWs, wasn't hard to get the front axle through. But I can see how it could shift a bit and be a problem.

In any case ( as you will see from my earlier post) I undid everything and reassembled all the pieces and now it seems fine. So perhaps the axle carrier tube was misaligned before? My only doubt remains, if I keep tightening the lock nut at the end of the axle, wouldn't that bring the stanchion tubes together and cause the wheel to bind again? or does the axle carrier tube prevent that? I would think that the designers would have built a shoulder into the axle, or a step so you couldn't keep pulling the stanchions together by tightening the nut.....

Thanks for your input.

And since you have a similar period machine- I just bought and installed a Tarozzi front fork brace. The right collar fits fine on the 38 mm stanchion. The left one is too tight- bad machining from the factory. Easy Dremel tool fix but kind of odd to have to touch up their work. Curious if you have one as well?

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NortonComm

Discussion Starter · #8 · Feb 4, 2020

rick81mhr900ss said:
Not this time; I used to have a fork brace on an old Laverda triple but left the Ducati as-is. That tube (bush) between the bearings inside the wheel is just one of those things; install the wheel one day it's a breeze but the next, you are fidgeting with a screwdriver or similar to align the bush with the shaft. Not an issue in my living room but at the side of the road with the bike supported with bits of wood, it's another thing altogether. The rear wheel is worse!

The loose bush scenario I suggested above is highly unlikely but I can't think of anything else that would explain wheel rotation stiffening up as it's axle bolt is tightened; the only part of the wheel in contact with the bike is the outer surfaces of those two bearings and the little speedo drive tab. The bush, if tight, will simply support the inner races as it is supposed to but if too loose then the inner races will be pushed inwards on both sides. These are roller bearings not thrust bearings so it's conceivable that they will jam if there is any significant displacement of the inner races.

I used to have a NortonComm too! A 74 850. Sold it a few years ago. Dumb, dumb, dumb.....

I went the opposite direction. I have had a 73 Norton Commando 850 ( since 1979) and liked it so much that I bought a 1974 850 in 2000. One's a cafe bike, the other is more of a roadster.

My dumb move ( 1995....) I was looking at an MHR and test rode it while the owner followed on my Commando. It was in excellent shape. He wanted 5 grand and that seemed like a ton of money and I had no real storage option so I passed. And I'd been riding a cousin's GSX, and in comparison the Ducati seemed sloppy and a bit stiff. Oh well........

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NortonComm

Discussion Starter · #9 · Feb 4, 2020

rick81mhr900ss said:
For reference, I just took a picture of one of my front calipers and disc from above. They are identical on both sides. Note how the caliper split is exactly centered to the disc:
View attachment 979733

I checked since your first note. Mine is identical to yours.

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NortonComm

Discussion Starter · #13 · Feb 6, 2020

rick81mhr900ss said:
Really useful pics and information here: Back to Classics

Thanks- I'd never seen Back to Classics before. Fantastic resource.

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NortonComm

Discussion Starter · #14 · Feb 6, 2020

Duccout said:
Hi,

Looks like you are getting there... It is not possible to pull the forks together because the right-hand fork bottom is free to slide along the wheel spindle. When you tighten the spindle nut, you are tightening the left-hand fork leg against the speedo drive ( you were correct in replacing that washer - as Rick says, the originals just dish, I had some thicker ones made in stainless). When tightening the wheel spindle, leave the pinch bolt loose, hold the spindle with a spanner and tighten the nut, then the pinch bolt. If you loosen the pinch bolt you will be able to push and pull the right- hand fork leg in and out along the spindle - find the centre point and then tighten the pinch bolt. Be careful that your problen is not connected to the fork brace, they can push or pull the fork sliders apart and make the forks bind.

Yep. I should have clarified that I installed the fork brace way after this front axle assembly problem surfaced, and disassembled it while I was troubleshooting. I think I am home free. A new stainless washer, combined with getting the axle carrier tube properly aligned seems to have done it.

I just finished drilling the rotors, installing a hydraulic steering damper and a front fork brace, in addition to sorting out the axle. Makes a much better handling machine.

Thanks all.