NC Front hub issues.

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Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

NC Front hub issues.

Postby Bevel bob » Wed Mar 28, 2018 12:11 pm

The wheel axle has always been a mare to refit, I assumed it was because of the non std mudguard and bridge loading the forks and also recent problems with damper body and circlip leaving the slider unsecured. A reworking of the guard to unload the forks and I was confident my problems were over, no such luck. I find the bearing spacer free to flop around and block the axle, also worry that the slack will load up the bearings when the axle is tightened.Has to be 5 or more thou clearance. Dont think the bearings can cope with this amount of displacement. Going to check the bearing housings are clean ,Don't think the bearings can be removed without damaging them . Options? ,make a longer spacer?, turn out the back of a housing,grind off 6thou or more from the back of a bearing outer track?. What do you think?.

blethermaskite
Posts: 477
Joined: Thu Mar 01, 2018 1:06 am
Location: northern ireland

Re: NC Front hub issues.

Postby blethermaskite » Wed Mar 28, 2018 3:39 pm

Hi,
Had this problem a few times, just lengthen the spacer, if you have access to any type of welding gear run a little bead of weld round the end of the spacer then turn or grind or carefully file back down to your required length, I have oxy/acetylene equipment so I sweat a little 'sifbronze' on to the end of a dodgy spacer and then turn it back down to fit reasonably tightly between the bearings, as you rightly say you don't want to load them up to take up the slack, also the spacer is the least valuable bit of the whole assembly and if you muck it up its pretty easy to replace.....unlike your front hub if you start trying to adjust the bearing position.
Cheers,
George

Bevel bob
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Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: NC Front hub issues.

Postby Bevel bob » Wed Mar 28, 2018 4:49 pm

Thanks for the advice, have to knock the bearings out and get a longer spacer. Despite all my care in getting the brace square the axle was still locking up when fitting the Guard. With the axle in position and smoothly turning I noticed the cast alloy pommels on the forks are not parallel , Its been like this from new!, All those years with stiff fork action. Probably a flimsy orriginal guard would flex enough to get by. If your forks are not right ,check this out.

double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: NC Front hub issues.

Postby double diamond » Wed Mar 28, 2018 8:25 pm

The stock bearing spacer is made of pretty lousy material. The much harder inner race of the bearings mashes the ends of the spacers leading to excessive axial clearance. Ideally, the spacer would be made of harder material that wouldn’t deteriorate. Brazing or welding will bring the spacer back to length but the material is still soft so your problem will eventually recur.

The other issue is that the spacer drops out of alignment with the bearing. Some manufacturers use washers on the bearing spacer to keep it in alignment. O.D. of the washer is near the I.D. of the cavity between the bearings and the washer slips over the O.D. of the bearing spacer and welded in place. I’ve seen some spacers with a washer on either end of the spacer but one washer in the center of the spacer is adequate.

If you heat the hub the bearings come out without much heavy-handedness. Pressing out with a blind bearing puller in place would be the best approach to save the bearings but they feel ok after drifting them out if the hub has been heated sufficiently.

Matt

ranton_rambler
Posts: 439
Joined: Sun Jun 04, 2017 11:33 am
Location: Stafford UK

Re: NC Front hub issues.

Postby ranton_rambler » Sat Mar 31, 2018 5:00 pm

Put new bearings in my 175 hubs today. The spacers have a collar on each end which keeps them centralised, similar to what Matt mentioned. The length seems to be such that they are trapped between the inner races when the bearings are in place. Spindles go through easily on both. Hopefully the spokes and rims will turn up soon.

Ian

Bevel bob
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Location: Bromley Kent UK.

Re: NC Front hub issues.

Postby Bevel bob » Mon Apr 02, 2018 3:31 pm

Thanks guys,After removing the bearings I find the spacer measures bigger than the distance between the housings!, the bearings must have not been fully inserted by the previous clot. Put it back together and it spins ok however there is a curious rythmic trick trick noise that appears to eminate from the speedo gears ,also the speedo plate now looks to be slightly more into the hub (bearing now fully in?) .Might try a shim between bearing and plate.

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: NC Front hub issues.

Postby Bevel bob » Tue Apr 03, 2018 8:43 am

Had a re-think, its likely that the spacer is home made and is about 25thou longer than the space between the bearings ,which means the bearings cannot both sit fully in the hub ,one can be fully in and the other 25 thou out ,this can work both ways so its possible that the speedo drive can be missaligned. The spacer is just a straight tube ,anyone else have one like this ? or a proper spare with flanges? A measurement check would also be helpfull. There should also be a protective cup and felt over the speedo drive?.

DBDBrian
Posts: 197
Joined: Mon Mar 30, 2015 11:29 pm

Re: NC Front hub issues.

Postby DBDBrian » Tue Apr 03, 2018 4:41 pm

Hi Bob, it would seem your findings are the norm. I have just checked a hub I have at hand, and it is all original to the best of my knowledge . The bearing spacer is indeed not a great piece of engineering, as to the material or it's design.
It is a parallel tube with no external flanges, and way off round, it also has far too much clearance on the spindle, approx 2mm, which compromises it's location centrally on the bearings inner races.
It is 2.487" long, 0.027" longer than the distance between the flanges in the hub, I presume this was done to alleviate the need for accurate machining of the spacer. As I see it, this arrangement can not hold the hub in position, unless one of the bearings is positively retained in it's housing, (as are many types of hub), and as you say, it effects the location of the speedo drive, (also the brake plate) dependent on which bearing is home in it's housing, if either ?
This is the hub I intended to use for my rebuild, so when I refurbish it, I will be making a new spacer of the required dimensions, with a small external flange in the middle, to assist with locating the spindle.
I hope this confirms you thoughts, as it has certainly brought it to my attention.

Brian
Brian
Made in England

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: NC Front hub issues.

Postby Bevel bob » Tue Apr 03, 2018 5:56 pm

Thanks Brian, that is exactly the response I needed and more or less confirms that what I have is normal ,and not good enough!.Hopefully both of us can now put things right.With the bearing in the speedo side knocked fully into the housing I find that a rib on the speedo plate appears to rub on the hub internal surface ,so i may well be glueing a shim on the back of the plate or to the bearing inner.A big shim behind the bearing (in the housing)would be better though.I may also also need a washer on my axle (a stainless repro) as the shoulder is too short allowing the tommybar to contact the fork slider before the axle is fully home.If the bearing spacer is too restricted in movement it will make it hard to knock the bearings out to replace. A bent or tight guard makes it impossible to fit the axle as it pulls the legs out of line. perhaps a 25/27 thou shim behind the speedo side bearing would fix it all??.

LaceyDucati
Posts: 521
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Location: Wales UK
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Re: NC Front hub issues.

Postby LaceyDucati » Tue Apr 03, 2018 8:12 pm

You are correct about the spacers being of poor quality/fit and that both bearings cannot seat on the outer race. It is quite a normal design to only seat one bearing as it would be near impossible to tolerance both components (hub and spacer) to sit perfectly. Certainly in the period and at sensible cost. However retaining one bearing with a circlip or lock nut would have been a design improvement. I had some new case hardened spacers made with ground faces and closer fitting bore, which I have available.

Some of the issues with Ducati hubs are made worse by modern bearings having narrow radial side faces. Surprisingly there is no specific width for this feature of a bearing and it has varied over the years and from make to make. Some early bearings have a radial inner face width of around 3mm, whereas some modern bearings are as little as 1.2mm. Some SKF and NSK bearings have wider faces, which is what I fit and sell for wheel use. These narrow face bearings cause the faces of components to wear and can cause the rear backplates to split

Nigel


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