Front wheel bearings.

I have done a lot of work to the bike and it was time to change the tires, I was given a set of new Gremeca front rotors and bolts with the bike and thought it might be a good idea to do the lot, Once the wheel was removed, I felt the wheel bearings and they were brinelled, I took the bearings and seals out of the hub and noticed they were C3 clearance which has larger clearance that the C2's. the seals were also cooked and hard from the heat, I thought I better get to the bottom of the bearing issues as they should last a lot longer than 40K, I measured up the bearing bores and faces where the bearing bottoms out on and measured the spacer, the spacer was .4mm longer, I fitted the first bearing and using a ground straight edge confirmed the spacer was too long.

If you fit the bearing with a longer spacer it will bottom out on the inner race as you press it in on the outer race and preload the bearing, removing the clearance and applying a side load that the ball races were not designed to handle, this is what destroyed the bearing in the wheel as they were worn on the outside of the groove, if you are having a problem with the life of the front bearings, I suggest you look at the spacer length, I flicked out the seals from the new C2 bearing and packed them with a good quality synthetic grease, then machined the spacer to length, the seals can be removed without damaging them using a sharpe scriber on the OD of the seal, I did a bearing course with SKF and the fitment of the bearings determine their life, heating the housing and cooling the bearing is the best method but is out of the question with a motor cycle wheel, the next best method is to draw the bearing into the house using a threaded rod and the correct size spacers that applies load to only the OD of the bearing.

It is now all back together and just waiting for the rain to stop to see how it goes, the wheel spins freely but has a small amount of drag due the new seals.

It is normal for a spacer to be too long. You have to seat one bearing fully then install the other bearing to the correct depth so that there is no preload. The second bearing won't be installed at full depth.

I have spent the last 50 years of my life as a machinist and high speed rotation equipment specialist in the power generation and oil and gas industries, I can assure you that is not how it works as the bearing has .1mm clearance radially, can you tell me how you keep the clearance at .1mm radially by installing the bearing this way, both bearing are meant to be up against the faces in the bore and the spacer is set to keep the clearance in the bearings, as the bearings are not designed for end load and this is why the bearing failed on my bike.

I am a motorcycle mechanic and replace bearings regularly. I can assure you what I said is correct. The Moto Guzzi manual doesn't spell it out but I  have included a diagram from a Suzuki manual showing how they want the bearing installed with clearance. Of course the side with clearance is for a GSXR. It might be the other way around on a GRiSO.

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Thanks for that, So why was my bearing brinelled on the outside due to overloading, they were pressed in without clearance, How do you know when the clearance is right as you have no way of knowing due to the limited space as the inner bottoms out on the spacer while you pressing on the outer, and from what I have seen there is a lot of wheels bearing issues on Moto Guzzi's and  I have never seen anything like this in my life with bearing spacers.

I do it by feel. I heat the hub with a heat gun and freeze the bearing then tap the bearing in until it contacts the spacer ensuring the spacer is square.

In the Suzuki diagram they are using a special tool to draw the bearing in. If the tool contacts the inner and outer race at the same time I suppose when the inner race contacts the spacer that will stop the bearing being drawn in further.

Before I remove bearings I measure the installed depth of the bearings to give me some clues to work with.

With a GRiSO I would say the RH bearing is fully seated and the LH bearing is installed second to the appropriate depth. The bearing that is installed to full depth is normally on the side of the wheel that is pulled up hard to the fork, not the side where the axle floats in the fork and is ultimately clamped by the pinch bolts.

I had a look at the set up I ended up with, on the internet, everyone belts them in with a hammer and a socket, this will destroy the bearing as it bottoms out on the inner bearing and the spacer, this is why mine were RS,  I made a puller, the discs were .5mm smaller than the bearing OD, drilled a 12.5mm hole though each one, I removed the left hand bearing as the right hand side is fixed with a spacer to the fork leg and bought a replacement bearing, I made a high tensile steel shim .5mm thick and drew the bearing in with a piece of 12mm all thread, it makes sense what you said and only works if you draw the bearing in against each other, that spreads the load across the inner and outer bearing faces without loaded the inner race and once it is seated it maintains the clearance. The wheel now spins very freely. Thanks again and it is always worthwhile to get another set of eyes on the job.

Moto Guzzi virgin wrote:

Thanks again and it is always worthwhile to get another set of eyes on the job.

I am happy to hear you have got a good result.

I am not the most experienced mechanic around (I have had other careers in my 53 years) but I work as a mechanic because I am genuinely interested in doing the right thing by people and their motorcycles. There's a lot of things that can only be learnt by experience and I am happy to pass these things on.

You obviously have a good eye for mechanics and one of the big things is knowing when something that should work isn't working and then finding out why. No one knows all the answers and every day I search workmates and google for answers.  [You must be registered and logged in to see this image.]

I was a senior mechanical technician offshore for 13 years before I retired and have worked on many things including gas turbines and every aspect of high-speed rotating equipment, it helps to have a machining background as you have a feel for thing, If you install them with the tool I made, you do not have to check the clearance, as soon as it pulls down onto the spacer the clearance is set on both bearing as the inner and outer bearings are flat. the correct position for the radial clearance.

Moto Guzzi virgin wrote:

I had a look at the set up I ended up with, on the internet, everyone belts them in with a hammer and a socket, this will destroy the bearing as it bottoms out on the inner bearing and the spacer, this is why mine were RS,  I made a puller, the discs were .5mm smaller than the bearing OD, drilled a 12.5mm hole though each one, I removed the left hand bearing as the right hand side is fixed with a spacer to the fork leg and bought a replacement bearing, I made a high tensile steel shim .5mm thick and drew the bearing in with a piece of 12mm all thread, it makes sense what you said and only works if you draw the bearing in against each other, that spreads the load across the inner and outer bearing faces without loaded the inner race and once it is seated it maintains the clearance. The wheel now spins very freely. Thanks again and it is always worthwhile to get another set of eyes on the job.

Well, I don't ever intend to do this since I don't ride my bike that often and I think it will last forever. But what you said is so fascinating that I wonder if you couldn't provide an image for others to utilize. I'm kind of technical but nowhere near the capability is an experience of the commenters here so an image would be very useful for comprehension. Fascinating.