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Loose rear wheel bearing in wire-spoke wheel

Michael Moore

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I was surprised and dismayed to lean the wire-spoke rear wheel from my SP project to the right and have the drive-side wheel bearing fall out on the floor. Finding a major issue right off the bat with a project is mildly discouraging.

I've learned that the steel inner hub is a replacement part for the cast wheels (#14632250), but not for the wire wheels, though it appears the later part can be modified to fit.

I'm not sure retrofitting the later part makes much sense if it would also eventually loosen up on the bearing. Buying a piece of 4140 or 4340 steel and making a new hub might give me a superior part to OEM if Guzzi didn't use a very high-spec steel. Since the brake-side bearing is carried in a separate aluminum casting the steel hub only needs the one bearing bore done before the completed replacement hub is parted off of the bar, which helps to simplify the process.


Has anyone pressed the steel hub out of the wire wheel alloy hub, and if so was it pretty straight forward? The wheel is currently built up and has a new tire/tube installed on the new Akront rim, so popping it all into the oven to loosen the fit between the steel and aluminum doesn't seem a good idea. :eek: I'm thinking that instead I might aim my heat gun on full blast at the alloy hub and maybe have it also sitting on an electric hot plate/range element until it gets around 100C before putting it in the press. For assembly the steel hub could be cooled to help reduce the interference fit into a hot wheel casting.

thanks,
Michael
 

john zibell

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My recommendation is to get a new bearing and if it is a slip fit, use Locktite bearing and sleeve retainer on the outer surface. Also a machine shop may be able to make a shim/sleeve to tighten the fit.

Did a parts lookup and since the first SP they were cast wheels. Where did you get spoke wheels for the project?
 

Michael Moore

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John, I presume they were off a T3 or some other bike that came with spoke wheels. I didn't care for the looks of the "bent spoke" cast wheels and wanted wider rims so I went hunting for other hubs. That would have happened around 25 years ago so details are only veglia familiar at this time.

Adhesives often want a small but present bond line thickness, some Loctite guides mention machining for a minimum .002" radial gap. There's about a .0005" difference in radius here and while 620/640 sleeve compound is good stuff, that might not offer enough peace of mind. .0005-7" shim stock is getting pretty thin for going into an interference fit. Bonding the bearing in might work fine, but then it might not

If the steel hubs lose their fit often enough to be offered as a replacement part (for the cast wheels) it may be that the design/material is marginal, so stepping up to a higher strength steel might be in order to get the nominal 2mm wall hub to hold the fit. I wouldn't presume that Guzzi spent any more money on the steel spec than they thought would be just good enough for a reasonable service life while being affordable to make, and it sounds like they may have underspec'd a bit. Or it may be that this hub was at the outer range of a tolerance when made and there wasn't enough interference fit + wall thickness to retain the bearing over time.

The cush drive plate has to move slightly on the outside of the steel hub so that limits the hub OD outside the bearing. I'll have to look to see if there's a possible swap (if I'm making a hub) of a smaller diameter but wider bearing that would have a similar load rating to the 6204 that would allow a thicker wall on the steel hub. If so, then maybe I can sleeve the hub down without removing it. Or I can make a replica hub of a strong alloy steel with an appropriate fit and hope it lasts better than the stock part did.

I would like to approach pressing out the hub with some confidence from someone else doing it successfully, though I suppose there are probably still some of these spoke wheels around if Mr. Murphy lends a hand. I've seen some photos of a cast wheel having a hub replacement, but not one of the wire spoke wheels.

cheers,
Michael
 

john zibell

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The reason they are a replacement part is not because of the bearing fit (yours is the first one I've hear of with this problem) but because of spline wear. In my opinion you are making this more difficult than it needs to be. You might try calling Harper's Moto Guzzi to see if they have one in stock, or a good used part. If from a T-3 or G5, the part number is 14 33 52 03
 

Michael Moore

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The center hub has no splines, those are on the big cush drive disk with the part number you supplied. Here's the cast wheel center hub which carries the wheel bearing and allegedly can be trimmed slightly to match the hub in the wire spoke wheel. It is a pretty straight forward lathe part, 3" long by 2" OD (roughly). Note the Guzzi part number in the image, it is not the cush drive part.

WheelSpcr.jpg
 

john zibell

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The center hub has no splines, those are on the big cush drive disk with the part number you supplied. Here's the cast wheel center hub which carries the wheel bearing and allegedly can be trimmed slightly to match the hub in the wire spoke wheel. It is a pretty straight forward lathe part, 3" long by 2" OD (roughly). Note the Guzzi part number in the image, it is not the cush drive part.

View attachment 23114


Sorry for the mis-understanding. The terminology you used led me astray. I've have worked on may wheels and haven't had this issue. Looking at the G5 parts listing I think you are talking about part number 17634150 Is that correct? If so I'd just replace it. I believe you can get one from Harper's.
 

Michael Moore

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John, that 17634150 is a spacer (probably 20mm ID) that goes on the axle. It appears that then presses against the outside of the inner race of the right wheel bearing when the axle nut is tightened. As you can see from the photo in my last post the replacement steel hub is a tube about 75mm long by 52mm OD and the right wheel bearing presses into the end and the large cush drive plate with the splines rides on the outside of the hub above the bearing.

The wire wheel fiche don't list the steel inner hub as a separate part. Only the "mag" wheels have it listed separately. Guzziology says the later part can be modified to fit the wire wheel, so the options appear to be either buy the later part and machine it to fit or make one from scratch or find a complete hub that hasn't lost the interference fit.

This loss of interference fit may not be a common issue, but I'm used to my projects being "exceptional" for the weird issues they present. :)
 

Michael Moore

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I had the idea of sleeving the ID of the hub and fitting two 6004 bearings (smaller OD) to replace the 6204. I ran that past a couple of friends who have manufactured their own cast wheels and racing wire-spoke drum brakes, and I was told that on the cast wheels a 6004 on the brake side and two 6004s on the drive side was what was used without issues. This will give me a thicker sleeve that is also longer than the 6204 bearing so things should be reasonably stable. The two 6004 bearings combined have higher dynamic/static/fatigue load limits than the single stock 6204 bearing.

This will avoid pressing the center steel hub out of the hub casting and I will only need to make a new (shorter) center spacer between the wheel bearings and then the short steel sleeve. I'll bore the sleeve ID to size after it is installed to the hub.

It is nice to have expert friends available for sanity checks on ideas like this! :)
 
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