Nasty CARC!

The bevelbox on the CARC system is generally pretty robust. The one Achilles Heel it has is the light preload on the pinion bearings supplied by the nut and the fact that it is held there simply by a lockwasher. For some bizarre reason Guzzi don't Loctite it and if the bearings settle or wear the preload is lost, the nut comes loose and things go pear shaped fairly quickly.

First symptom will be noise from the final drive on the over-run. If you notice this stop riding immediately. Not only could it preceed a catastrophic failure but also if you stop it there and then it may well be possible to save your final drive. I can't stress how important catching it early is.

If you don't and continue to ride the consequences may be terminal. Michael has just stripped Peter Hughes's box after he continued riding it for a while. Unfortunately it's fed bits of lockwasher all through everything and the results are terminal.

Sorry but there's no saving this one.

[You must be registered and logged in to see this image.]

This is the pinion nose bearing. Most of the other bearings in the box and reactive bridge look much the same.

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Now if you do catch it early and there is no crownwheel or pinion damage it is, despite what the factory may try to tell you, quite possible to rebuild the entire reactive bridge and therefore the bevelbox. My guess though is that very few shops would be willing to try it, either because they don't have anyone with the skills or for liability reasons. It's this sort of numbskull 'Built in obsolescence' that makes my blood boil and we won't have a bar of it. We can at least look at your box and tell if it's salvageable and if we can rebuild it you can bet your arse we'll be Loctiting the living Bejasus out of the pinion nut as it's preloaded so the bastard won't be coming undone again!

Oh, and as an indicator that this sort of repair is quite possible my box on my GRiSO played exactly the same trick. I caught it early, cleaned everything thoroughly and didn't even replace any of the support bearings! Just replaced the nut and lockwasher, Loctited and preloaded to about 120 inch pounds on the nut before bending up the tang on the new lockwasher. That was nearly 50,000km ago and it's still running silent and strong.

Arse!

&

Bloody Hell Pete, that is a timely message.
My GRiSO has recently started to rumble on the over-run.
It's in the garage now and I was about to investigate this weekend.
Thanks for the advice. Hopefully I'll be able to repair it.
Cheers, Andrew

Displaying yet again my ignorance, can someone please explain the overrun to me and what it should sound like.

When you roll off the throttle and decelerate using engine braking.

As for sound? There should be no noticeable difference in noise when accelerating or decelerating. If you have an issue you will initially notice a slight noise when you roll off the throttle. Within a short period of time the noise on the over run will become a howl and/or a growl. This is bad.

Thanks for that Pete. I very much rely on engine braking, typically only using the rear brake when actually coming to a halt and the front brake very very little at all. All continues to sound good but thanks for alerting me (and all of us on the Forum) about this potentially nasty issue. Gertie has now done 90,000km - largely thanks to you and largely despite the local shaved ape, whose door I no longer darken!

Looks like a preemptive strike should be in order!

Pete,

For those looking to accomplish the preventative maintenance, are you recommending your procedure be accomplished on #2 in the attached?[You must be registered and logged in to see this image.]

Nope, that's the seal holder. The pinion nut isn't shown.

Probably the best bet as far as preventative maintenance is concerned would be to guide a few drops of Loctite 'super wick-in' down onto the threads of the pinion and nut through the opening in the seal carrier. Super wick in is actually built to be applied to tightened nuts and is supposed to wick down the threads. It sounds a bit implausible but Loctite make good products and have no need to bullshit.

I like the wicking locktite idea better than the idea I had of tearing things apart!!!

Pete Roper wrote:

When you roll off the throttle and decelerate using engine braking.

As for sound? There should be no noticeable difference in noise when accelerating or decelerating. If you have an issue you will initially notice a slight noise when you roll off the throttle. Within a short period of time the noise on the over run will become a howl and/or a growl. This is bad.

Hi Pete,

My bike makes a rolling noise, mostly noticeable between 50-80 km/h, that sounds to me like a bearing noise. Not very loud, but anoying....
To be honest I cannot say since when...I don't know if it increased gradually and sneaked on me...
Openning and closing the throttle doesn't seem to make any difference on that noise. When riding, if I open the clutch (carc unloaded) and shut the the gas I still hear it.
Could it be the situation described by you?
If that would be the case, even in an early stage, would I find metal particles in the carc oil?

Many thanks,
Matias

Take the bevelbox off the swingarm. If there is oil in the swingarm and down the throat of the bevelbox where the pinion pokes out you may have a problem. If there is oil it means the front seal has let go. This can occur when the nut's preload is lost. You can see the nut down the throat of the seal holder. See if it moves in relation to the shaft of the pinion by poking at it with a small, thin screwdriver.

Thanks Pete.
It''s possible to remove the bevelbox without disassembling the swingarm?

Well you don't remove the swingarm but it's brake off, wheel off disconnect the torque arm and drop the box off the swingarm.

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