Guzzi 5-speed gearboxes

OK, well, I've got my Quota's gearbox opened up. I was expecting the
output bearing to be shafted (boom boom) but it feels silky smooth, with
no obvious play.

All else seems fine, except, looking at the fifth gear teeth under a
powerful magnifying glass, it's clear that the teeth are pitted on one
side.

As the noise was a piercing whine, almost a whistle, that disappeared
when the throttle was closed, I'm guessing that the gears are fucked.
Luckily it's the only gear on one of the shafts that isn't integral with
the shaft itself.

I've been tempted to replace the output bearing as well since the gearbox
is opened up, but in all honesty I think I might give that a miss as it
seems OK, though I do need to replace the oil seals. The output bearing
is the lighter, plastic-caged version that, according to Guzziology, Moto
Guzzi started using a few years before my bike was built.

I can't see anything else that could cause the very gear-specific whine;
all the gears are helically cut and all spiral in the same direction, so
it's not as though fifth puts an unusual end-thrust on either shaft. If
it were another gear's needle rollers then I'd have thought that it'd
whine when any other gear was engaged.

To other Guzzisti: does this sound sensible?

 

I'd still change the bearing for one with a metal cage personally. i've not
had good experience with the plastic cage variety (although not Guzzi
related).
I'd reassemble (do you have to shim up the later boxes?) and just use a good
fully synth gearbox oil plus the obligatory squirt of the appropriate guzzi
recommended magic additives (if applicable to your later gearbox).
For the record, I've not rebuilt one of oyu later boxes, only the old 80s
5-speed types. My box on the trike has done >190k miles (only 23k ish as a
trike though) with no rebuild so far.
JB

 

It's just a standard 5-speeder on the Quota: they didn't start using the
six-speeders until the 1100 Sport & V11 models, I think. So yes, they do
need shimming. As I'm probably only replacing one gear pinion set, I
doubt that the shimming will change by much; the gearbox wasn't silent on
shifts, but certainly wasn't a bad box before I dismantled it. Gawd knows
what it'll be like afterwards! I suppose I ought to check it, though.

Guzzi only specify MoS2 additive for the bevel box on these models,
though I have put the odd left-over squirt into the gearbox.

Nice to know!

 

Did the noise occur in all gears or just fifth?

The pitting on one side is certainly consistent with the whine only being
there with the thottle open, with it closed, the load moves to the other
side of the teeth. If it does it in all gears, look more closely at the
rest of the gears.

 

That's what I was thinking

It's just fifth. The other gears are generally audible, but no more
than the V11's, I'd say. I think it took a while for me to notice it
because it appeared gradually and I was using the bike to commute on
open 'A' roads & dual carriageways (what's the US equivalent?) and I
always wear earplugs for that sort of journey. I only really noticed
that something was amiss when I trundled to the shops without
earplugs: fifth produced a whine that was quite piercing at times.

Ah, well, it's only money.