Small blocks—Why the left-side rubber inserts in the rear wheel?

[Dirk_S]

Cush rubbers are common on bikes. On chain-drive bikes, they’re on the left side, sandwiched between the sprocket and hub to prevent damage and cushion the torque on the hub. On the small block Guzzis, these cush rubbers are on the right side, protecting the hub from the final drive dogs. So, why are there still rubber cushions on the left? I presume they’re for vibration damping, but I’m no engineer. Pics for reference:

[Kev m]

First off it sounds like you think the side has some significance and assume that all chains are on the left. The side is just a function of design and it doesn't have to be left.

Both I believe regardless of side or chain vs shaf the function is to dampen driveline lash, in both on and off throttle input changes.

[Dirk_S]

First off it sounds like you think the side has some significance and assume that all chains are on the left. The side is just a function of design and it doesn't have to be left.

Sorry, I should’ve said generally on the left side. Every, or nearly every chain-driven bike I’ve ridden or looked at, the chain has been on the left. Regardless, i think I’m still correct in my understanding of their purpose. or maybe I’m simply not observant enough, quite possible.

Both I believe regardless of side or chain vs shaf the function is to dampen driveline lash, in both on and off throttle input changes.

But the left side of a Guzzi small block rear wheel has neither a sprocket nor a final drive acting upon it. The left side cush rubbers press between the inside of the hub and the brake rotor. Seems to me the right side cush rubbers are doing that driveline lash damping—are the left side cush rubbers also in some way?

[Perazzimx14]

Wonder why BMW is sans cush drives on their shafties?

[Kev m]

Sorry, I should’ve said generally on the left side. Every, or nearly every chain-driven bike I’ve ridden or looked at, the chain has been on the left. Regardless, i think I’m still correct in my understanding of their purpose. or maybe I’m simply not observant enough, quite possible.

But the left side of a Guzzi small block rear wheel has neither a sprocket nor a final drive acting upon it. The left side cush rubbers press between the inside of the hub and the brake rotor. Seems to me the right side cush rubbers are doing that driveline lash damping—are the left side cush rubbers also in some way?

Maybe I didn't describe it well, but they are all doing driveline lash, both on and off the throttle. And wherever the input comes in, including the sprocket which causes movement/lash between the wheel and feeling as it grabs or releases.

[DoubleGuzzi]

Dirk, I understand what you're asking, when others don't.  Perhaps it helps stop a ringing noise from the disc rotor - very unlikely and just speculating. Heck knows what other purpose they could have; I'll take a closer look when I reassemble the rear wheel on my V7C.

[Dirk_S]

Maybe I didn't describe it well, but they are all doing driveline lash, both on and off the throttle. And wherever the input comes in, including the sprocket which causes movement/lash between the wheel and feeling as it grabs or releases.

How do the left side rubbers provide cushion for drivetrain lash if they’re not directly contacting the drive train?

Dirk, I understand what you're asking, when others don't.  Perhaps it helps stop a ringing noise from the disc rotor - very unlikely and just speculating. Heck knows what other purpose they could have; I'll take a closer look when I reassemble the rear wheel on my V7C.

That’s my guess, too. The small block rear hub is big, light, and a bit chasmic in material. I could see them simply used for vibration or sound damping.

[SIR REAL ED]

How do the left side rubbers provide cushion for drivetrain lash if they’re not directly contacting the drive train?



That’s my guess, too. The small block rear hub is big, light, and a bit chasmic in material. I could see them simply used for vibration or sound damping.

What does the drive mechanism look like?  It is only driving small round pins that fit in the holes in the red cushions?

Picture please.

[Dirk_S]

What does the drive mechanism look like?  It is only driving small round pins that fit in the holes in the red cushions?

Picture please.

I’m not going to say publicly how long it took me to understand you were using sarcasm.

[Kev m]

How do the left side rubbers provide cushion for drivetrain lash if they’re not directly contacting the drive train?



That’s my guess, too. The small block rear hub is big, light, and a bit chasmic in material. I could see them simply used for vibration or sound damping.

Wait what?

On what application are the rubbers not on the driveline?

On my smallblocks they go between the wheel hub and the final drive hub?

On the JAPanInc products I am picturing they go between a sprocket hub and wheel hub.

What are you showing in those photos?

[Dirk_S]

Wait what?

On what application are the rubbers not on the driveline?

On my smallblocks they go between the wheel hub and the final drive hub?

On the JAPanInc products I am picturing they go between a sprocket hub and wheel hub.

What are you showing in those photos?

Talking about the rubber cushions on the left side (non-drive side) of a Guzzi small block, that date back at least to the early 00s Nevada and up to 2020 (not included on the newer style E5 wheel).

[DoubleGuzzi]

What are you showing in those photos?

Have you never removed the rear disc rotor? Seems like it.

[Dirk beat me to it!]
A rubbish Fowlers diagram, where number 1 doesn't represent what both Dirk_S and myself have seen..

[mhershon]

When I replaced the wire-spoked wheels on my v7 with cast wheels, I had to swap the rear brake disc. I noticed that that one wheel type had rubbers on the disc side and the other did not. The disc bolted up the same way in either case.

[DoubleGuzzi]

I was gonna jokingly suggest leaving the rubbers out to reduce unsprung weight, hence making the bike sportier. 

[Dirk_S]

When I replaced the wire-spoked wheels on my v7 with cast wheels, I had to swap the rear brake disc. I noticed that that one wheel type had rubbers on the disc side and the other did not. The disc bolted up the same way in either case.

Moto Guzzi shows those rubbers used for both cast and spoked wheels, so either you’re missing the rubbers for your cast wheels, or Guzzi didn’t really put them on ALL of their V7s and Nevadas from 2004-2020.

I actually just removed the rear wheel in order to put the rubber spacers back in—I had forgotten to do so when I built the wheel—and remembered that the spacers/bumpers/cushioning rubbers actually sit a little proud when mounting the brake disc. So, maybe it’s to damp out the brake disc resonance. The rear rotor is not a floating disc if that helps sway the argument.

[Kev m]

Ooooooooooooooooooo ooooooooooohhhhhhhh h.

Yeah, I've not had to replace the rear disc on either so correct I've not removed it on them.

And uh yeah, ok, that's weird, but then I'd say 100% harmonic vibration and probably 99% unnecessary.

* Shrugs *

[Dr. Enzo Toma]

Wonder why BMW is sans cush drives on their shafties?

I suspect that might have to do with the paralever shaft design. I'm not familiar with Moto Guzzi CARC models, but aren't they without cush drive rubber dampers at the wheel as well?
There are some other interesting alternatives to cush drives out there, like Harley's compensator sprocket.

Looks like an explanation for the rubber brake rotor isolators from years ago on this forum is to address squeal.
https://wildguzzi.com/forum/index.php?topic=67641.msg1043693#msg1043693

[DoubleGuzzi]

Looks like an explanation for the rubber brake rotor isolators from years ago on this forum is to address squeal.

Seems that I'm maybe not so wacko after all. 

[SIR REAL ED]

I’m not going to say publicly how long it took me to understand you were using sarcasm.

I was actually serious.  Those little square-ish indentations in the red blocks look like they are only 1/8" deep.

Obviously they must only look that way in the picture, and are much deeper in reality, right?

[SIR REAL ED]

This is a great thread.  My guess would be to dampen/reduce noise and probably not very effective.

Unless of course, one is using the wrong gear oil in the final drive.....

[Dirk_S]

I was actually serious.  Those little square-ish indentations in the red blocks look like they are only 1/8" deep.

Obviously they must only look that way in the picture, and are much deeper in reality, right?

Ah. The red is my highlighting the space in which the cush rubbers and drive dogs fit into. I looked, but couldn’t find a good pic of a V7 rear wheel with the drive-side rubbers seated. The small block has substantial dogs that slip in amongst the cush rubbers, which themselves straddle the radial spines on the hub.

All that said, my post is about the other side.

Edit: the ”square-ish indents” might simply be some extra space carved out for drive dog clearance, as the dogs sit right in that area.

[Dr. Enzo Toma]

This is a great thread.  My guess would be to dampen/reduce noise and probably not very effective.

I've had the same thought about the rubber isolators on some front sprockets, or the harmonic ring on some rear sprockets the first time I came across those. They seemed like silly little designs, but I learned from trying aftermarket sprockets without them that they are effective and if a bike has them from the factory then they're probably there for a reason that is good enough (noisy enough) to justify their cost.

[Moparnut72]

They are there to help absorb the vibration from the engine. Engines don't have perfectly smooth output, each cylinder firing produces a push that kind of dies out at the end of its stroke. Also firings don't come evenly spaced, the rubbers are there to adsorb some of the shocks. As mentioned Harleys use a device called a compensator which is a device with a set of spring loaded ramps that climb up each other to absorb vibration, best I can describe it. Some Harley owners will replace the miserable failure prone compensator with a sprocket. It works but increases wear and possible failures of the transmission. I don't know about current BMW's but Airheads have an elongated ball which fits in a similar socket under pressure from a spring. Under torque and vibration from uneven power strokes, although flat twins are generally quite smooth due to engine design, the ball and socket try to push away from each other absorbing socks and vibration. I have tried to explain it as best I can. BTW Harleys aren't all the same, Big Twins have the drive pulley on the left side and the Sportsters have it on the right side.I don't remember my Sportster doing it much but big twins will clank pretty well if the drive line is left engaged a real low rpm as the ramps come to the end of their range.
kk

[Huzo]

They are there to help absorb the vibration from the engine. Engines don't have perfectly smooth output, each cylinder firing produces a push that kind of dies out at the end of its stroke. Also firings don't come evenly spaced, the rubbers are there to adsorb some of the shocks. As mentioned Harleys use a device called a compensator which is a device with a set of spring loaded ramps that climb up each other to absorb vibration, best I can describe it. Some Harley owners will replace the miserable failure prone compensator with a sprocket. It works but increases wear and possible failures of the transmission. I don't know about current BMW's but Airheads have an elongated ball which fits in a similar socket under pressure from a spring. Under torque and vibration from uneven power strokes, although flat twins are generally quite smooth due to engine design, the ball and socket try to push away from each other absorbing socks and vibration. I have tried to explain it as best I can. BTW Harleys aren't all the same, Big Twins have the drive pulley on the left side and the Sportsters have it on the right side.I don't remember my Sportster doing it much but big twins will clank pretty well if the drive line is left engaged a real low rpm as the ramps come to the end of their range.
kk

He…is…talking…about…the…brake…side.
I will suggest they are present to dampen out torque reactions from when ABS kicks in. I don’t have a V7, mine is a V85, but I would ask if the disc carrier engages into those blocks in any way.
Other than that, I’m clueless.

[DoubleGuzzi]

This is a great thread.  ..
Unless of course, one is using the wrong gear oil in the final drive.....

Nailed it! Speaking of puncture prone tyres.. 

[Dirk_S]

He…is…talking…about…the…brake…side.
I will suggest they are present to dampen out torque reactions from when ABS kicks in. I don’t have a V7, mine is a V85, but I would ask if the disc carrier engages into those blocks in any way.
Other than that, I’m clueless.

ABS didn’t come on the scene for small blocks until the V7 II in 2015/2016 (US), but the rubber blocks have been used since 2004 on the Nevada Classic. Note that the rear hub on the Nevada Classic in 2004 is the same hub used all the way through 2020, with variations in coating—bare or painted/powdercoated/whatever. Conversely, the Breva during this period, using a cast wheel with a smaller hub, does not utilize the rubber blocks, and Nevada models pre-2004, with a similarly large hub as later years, also do NOT use the rubber bocks. Fiche snapshots below:



When the fixed rotor is bolted on, the rubber blocks sit just proud enough that they create a bit of resistance against the disc carrier when torquing down. I’m not sure if they changed the design of the rear hub in 2004, or simply added the pucks—upon cursory search, it doesn’t appear that the rear hub could be purchased separately prior to 2004, but I suspect the pucks were at least a response to that resonance, considering it looks like a large, open drum that could be used to play Ween’s “Bananas and Blow” (steel drum reference for those who missed out on the Boognish wagon: https://youtu.be/IWrYNcv7fPk?si=SPIhAR-TfsvPiK8c)

[SIR REAL ED]

I've had the same thought about the rubber isolators on some front sprockets, or the harmonic ring on some rear sprockets the first time I came across those. They seemed like silly little designs, but I learned from trying aftermarket sprockets without them that they are effective and if a bike has them from the factory then they're probably there for a reason that is good enough (noisy enough) to justify their cost.

I agree.  Many variations exist.  They definetely reduce the noise of the chain meshing with the sprocket.

[SIR REAL ED]

Nailed it! Speaking of puncture prone tyres.. 

The first person to authoritatively state that you can absolutely remove the rubber blocks from the disc side of the rear wheel with no ill effects if you first install a quick shifter wins this thread!!!!

[SIR REAL ED]

When the fixed rotor is bolted on, the rubber blocks sit just proud enough that they create a bit of resistance against the disc carrier when torquing down. I’m not sure if they changed the design of the rear hub in 2004, or simply added the pucks—upon cursory search, it doesn’t appear that the rear hub could be purchased separately prior to 2004, but I suspect the pucks were at least a response to that resonance, considering it looks like a large, open drum that could be used to play Ween’s “Bananas and Blow” (steel drum reference for those who missed out on the Boognish wagon: https://youtu.be/IWrYNcv7fPk?si=SPIhAR-TfsvPiK8c)

I'm going with noise dampening for 300 Alex. 

After they already finalized the design of the hub and disc, and had hundreds of units ordered and in fabrication, early testing revealed a weird noise occasionally coming from the rear wheel during braking. 

The rubber blocks dampened out the noise, and they removed the paragraph from the owner's manual telling the buyer to stuff cotton in their ears before putting on their helmet.

The rubber blocks was a cheap easy fix.

What did I win Alex?

[Dirk_S]

I'm going with noise dampening for 300 Alex. 

…The rubber blocks was a cheap easy fix.

What did I win Alex?

Oo, sorry. You didn’t phrase it in the form of a question.

(Alex loved saying that, I bet)