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Discussion Starter #1 (Edited)
There are numerous threads discussing the rear hub on the 3 cylinder single sided bikes. A couple of concerns exist regarding this part of the bike.

1) Rear hub sprocket side nut has reduced torque after some time despite being pinned.

2) Rear hub sprocket carrier rubs against the housing.

I have 20,000 miles on my bike (2014 MV Agusta F3 800) and have done the rear hub servicing twice. This is something owners and shops quite often miss doing. In my case the hub looks to be in great condition but you can find pictures of hubs that have not done well. Every case is different but doing this service and applying to the hub correct torque is important.

In discussions with other members the topic of the center spacer was mentioned. MV has gone from an aluminum one to a steel one. I do not know if the decision was based on strength or because it avoids galvanizing/fusing of dissimilar parts. You can see in the picture that it is being held by a magnet. The parts diagram shows it and its part number for reference.

This part is available for those interested in replacing the aluminum one with steel.
 

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The perspective on that picture makes it look like the part will not fit into the hub. For clarification to others, the part is being held up by a magnet and is nearer in the field of vision making it look large.

This may be my observation issue only, but I thought i would clarify now that I see it for what it is.
 

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ON the subject of galvanic corrosion in the rear hub: There are dissimilar metals throughout the rear hub. The bearings are steel, the housing is aluminum, the pinch bolts are steel, the swingarm is aluminum, the axle is steel, the wheel nut and sprocket nut are aluminum, etc. The fact that the whole sometimes lives in a wet environment provides the electrolyte and you essentially have a battery. Adding more steel does not change this.

Corrosion protective measures will help.

None of this has any effect on the stack height through the hub as has been discussed. Dimensional stability in the manufacturing process is probably the culprit in the loosening of the sprockit side nut.

Hub-Cross-Section.jpg
 

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Discussion Starter #4
Yes.. the picture shows the spacer close to the lens and looks like a large part. I just wanted the hub in the background as a visual reference to what that came from.

When you say dimensional stability what do you mean? Manufacturing tolerances? Or that something is compressing and therefore allowing the torque to then be reduced when it is checked at a later time?

You are right that there are many places where aluminum meets steel. But the surface area of contact in other parts means you can easily overcome any fusion. The spacer has a potentially large surface area. Maybe aluminum is harder to manufacture in tight tolerance? Maybe having more steel in the solid stack means it will all expand and contract as one rather than the aluminum expanding more leading to its eventual shortening?

Cylinder heads made of aluminum contacting with steel blocks can lead to head gasket issues due to variable expansion for example. I wonder if this is the issue with the sprocket nut loosening?

For me and for MV the decision to go from aluminum to steel seems to have a few advantages.
 

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I'm going to throw this out for thought

RE: loosening of sprocket side nut.
It was mentioned in other related posts that the nut (pined) does not loosen; but the clamping force is reduced, giving the impression that the nut has ("backed off") loosened.

I suggest the culprit is the aluminum bearing spacer within the central hub is compressing under fitment clamping force, or the spacer is too short to start with.

My last bike a 2006 Buell Ulysses could experience similar outcome (assembled stack end up short) when the rear wheel bearings were replaced or simply when the rear axle was over torqued. That is, the aluminum spacer that set the distance between the left and right wheel bearing could be compressed (shortened) by over torquing the axle. This would place an unintended axial load on the ball bearing, which would lead to premature failure.
The wheel bearing selection was also part of the problem. As when the 2010 model came out, it had 3 wheel bearings and extra (proper) dust/debris seals.
 

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Discussion Starter #6
I reworded to reflect that it isn't loosening but rather the side load reducing as you are saying. It definitely isn't spinning loose. I also agree that it's either overtorqued or heating up naturally or from lack of lubrication. So the move from aluminum to steel seems appropriate. By the way the hat spacer is also steel. That means pretty much everything in the stack in my case other than the alloy nut is steel. So, for those doing a hub service please do and check if you have steel. If not, replace.

I'm going to throw this out for thought

RE: loosening of sprocket side nut.
It was mentioned in other related posts that the nut (pined) does not loosen; but the clamping force is reduced, giving the impression that the nut has ("backed off") loosened.

I suggest the culprit is the aluminum bearing spacer within the central hub is compressing under fitment clamping force, or the spacer is too short to start with.

My last bike a 2006 Buell Ulysses could experience similar outcome (assembled stack end up short) when the rear wheel bearings were replaced or simply when the rear axle was over torqued. That is, the aluminum spacer that set the distance between the left and right wheel bearing could be compressed (shortened) by over torquing the axle. This would place an unintended axial load on the ball bearing, which would lead to premature failure.
The wheel bearing selection was also part of the problem. As when the 2010 model came out, it had 3 wheel bearings and extra (proper) dust/debris seals.
 

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The F4 does not suffer with the sprocket nut loosening and it's the same hub and axle set-up,so how do you explain that?
I have a theory that the loose nut sindrome on 3 cylinder models could be caused by the cushdrive or the quickshifter.
The nut is not actually loosening because the lockring is holding the nut in the same position.So,there must be wear happening along the stack.
The action of the quickshifter with it's snapping force could be moving the sprocket carrier slightly directionally causing wear.
I have been trying to work this issue out for awhile since the problem came up.
I have sold my hubs to F3 owners and they have reported back to me that the problem is solved.
I still would like to know why it is happening though.
Not every 3 cylinder bike does it also,which is even more confusing.
 

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I have a theory that the loose nut sindrome on 3 cylinder models could be caused by the cushdrive or the quickshifter.
The nut is not actually loosening because the lockring is holding the nut in the same position.So,there must be wear happening along the stack.
The action of the quickshifter with it's snapping force could be moving the sprocket carrier slightly directionally causing wear.
Sounds plausible, as you say the nut is positively secured to the axle with the locking ring. However, my QS wasn't working from about 1,000 miles to around 6,000 miles and the loosening nut syndrome was still happening during that period, where I was either shifting clutchlessly in the traditional sense or actually using the clutch when shifting. Cush drive wear/compacting has also been an issue on a regular basis.
 

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The F4 does not suffer with the sprocket nut loosening and it's the same hub and axle set-up,so how do you explain that?
I have a theory that the loose nut sindrome on 3 cylinder models could be caused by the cushdrive or the quickshifter.
The nut is not actually loosening because the lockring is holding the nut in the same position.So,there must be wear happening along the stack.
The action of the quickshifter with it's snapping force could be moving the sprocket carrier slightly directionally causing wear.
I have been trying to work this issue out for awhile since the problem came up.
I have sold my hubs to F3 owners and they have reported back to me that the problem is solved.
I still would like to know why it is happening though.
Not every 3 cylinder bike does it also,which is even more confusing.
Does the F4 not have cush drive?
Does the OEM F4 use an aluminum bearing spacer?
 

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Discussion Starter #10
Can anyone with the loosening nut syndrome check if the old spacer and t hat was aluminum? Like I said there are some bikes with aluminum and some with steel parts. Checking parts catalog only shows me the latest part numbers and not what was on a bike when it did this.

My bike has steel and isn't showing this behavior... f3 800 2014 with abs and eas 1.0 quickshifter.

The engine pulsing is different between the f4 and f3... maybe something there as well since mitch is saying no problems reported with F4's.... but most F4's are not driven as hard or often as f3 as well.... so a different life cycle there typically.
 

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?

Does the F4 not have cush drive?
Does the OEM F4 use an aluminum bearing spacer?
Teeps;
1st Gen MVs have real cush drives that don't fail or eat rubbers......
They also have alloy bearing spacers like almost all bikes without issues

:grin2:
 

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Does the F4 not have cush drive?
Does the OEM F4 use an aluminum bearing spacer?
Yes,the F4 has a cushdrive and it uses the aluminium spacer as MV has used since 1999 without any issues with sprocket nut loosening.
My hub also has an aluminium spacer and after 200 sold not one has experienced this issue.
I do not own a 3 cylinder MV so I can only go by the information on the forum.
It is still a mystery.:surprise:
 

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Teeps;
1st Gen MVs have real cush drives that don't fail or eat rubbers......
They also have alloy bearing spacers like almost all bikes without issues

:grin2:
Agree, the Buell Ulysses rear wheel, with aluminum distance spacer, only had a problem when improperly serviced. Either when replacing wheel bearings or when over torquing the rear axle.

Guess I'll look for an exploded view of a 1st gen MV rear wheel.
 
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