Gearbox - Need urgent help!

Hi everyone,

I finally went for the main seal change.
Because I don't have the necessary means in my garage, I took the bike to a local workshop (the mechanic used to be a Moto Guzzi mechanic).

When he removed the gearbox to have access to the clutch and seal, he noticed that the "gear" below (it's not exactly a gear...) was loose on the shaft, so he unlocked the nut, tightened it, and locked it again with the locking washer.

Question: is this nut supposed to be loose on the shaft or tighten?

The urgency results from the fact that the bike is still on the workshop, and if waht he did was wrong he should correct it.

Your help is appreciated. Thanks a bunch!

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The clutch hub, the splined bit you refer to as the ‘Gear’ is a sliding fit on the splines of the shaft. If the nut has come loose the hub will have been chattering on the splines and may of worn them a bit so it would be a looser fit than normal. That in and of itself is fine. What is important is that beneath the hub, before where it sits on the bearing there should be an o-ring. It’s there in the diagram, it’s part # 2 but its location as indicated in the diagram is wrong! Interestingly it’s been wrong in every parts diagram for Guzzi gearboxes since five speed days! But believe me, it’s wrong.

The purpose of the o-ring is to act as a crush seal between the chamfer on the bottom of the hub spigot and the front of the bearing, part # 3 which is in the front case and supports the shaft. If the nut retaining the hub has come loose there is a very good chance the integrity of the o-ring will of been compromised and if the nut was loose enough for the hub to move on the shaft it is likely the lip of the seal, part # 4, which is fitted from the outside of the box has been compromised as well.

Since getting to it is such a complete bastard of a job it would be very unwise to reassemble it without replacing both the o-ring and seal. The seal has to be a Viton seal as well, not Nitrile. The factory seals are directional as well and while the best option a non directional seal works fine as well, as long as it is Nitrile. The seal also only has to be installed flush with the face of the case, not pushed in so far that it uses the bearing beneath as a register. If you do that it will blow immediately.

So, the order of assembly is; o-ring onto shaft, (Remove old one first!). Then install the seal. Then grease the sealing surface of the hub lightly and press it onto the shaft pushing it through the seal with a twisting motion. Then install a NEW lock-washer and finally put a drop of blue Loctite 243 on the threads and tighten the nut using the correct tool, NOT bashing it around with a punch and FB hammer! Finally bend up the locking tab on the lockwasher.

Done!

Thank you very much for the comprehensive explanation Pete

You’re welcome.

Hi everyone,

Unfortunately my problems just started ...
After the bike was assembled I took it for a test ride.
In the beginning all was right, but after a while (as the engine temperature raised, maybe...), when I was openning the gas uphill the bike started making a strange noise. It starts like a friction noise, but then it gets worse...like metal to metal. After a while the slightest oppening of the gas results in a very nasty noise...
The mechanic said that when he was assembling the gearbox to the engine (after replacing the main seal), the engine/gearbox union was resisting to close... Then he openned everything again and found out that the bit that receives the pressure from the clutch slave cylinder (through the rod) was out of position....He repositioned it and assembled everything again.
If he applied to much pressure on the clutch hub (on the gearbox input shaft), could that have caused any damage.

Pete, everybody, your help would be much appreciated...

Did he forget to put the thrust bearing in? Was it missing any rollers?

………

I'll check with him. He his taking everything apart again....

Pete, everything is OK with the thrust bearing...

A couple of questions:
The picture below seems to represent the shaft where the Clutch Hub is assembled (it is represented there...)
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However looking at this other picture it seems clear it is not...Not in the right position

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What am I getting wrong here Pete?
Also, what prevents the axle where the Clutch Hub is assembled to have axial movement?

Sorry if the questions seem silly, but I never worked on the gearbox...
I'm making the second question because I'm affraid the mechanic could have applied some axial force on this shaft when he forced the assembly of the gearbox with bit where the thrust rod applies force out of position.

OK, forget about that last mail.
I was confused while looking at the pictures, but after going to the workshop and look at the gearbox "in person" it got clerarer.
So, the shaft represented in the exploded view is in fact the clutch shaft.

I need, however, to clarify something...
I have noticed that if we tap on the clutch hub with a malet the shaft slides in. If we tap the other end of the shaft (salve cylinder side), the shaft moves in the other direction...
The reason we did this test was to determine if an undesired pressure aplied on the clutch hub during the assembly of the gearbox (like I said, the first time the mechanic tried to make the assembly the small disk that receives the clutch thrust rod was out of position) could lead to the noise I felt when I tested the bike.

Now, is there supposed to be any kind of mechanical means of avoiding the axial movement of the shaft, or is it normal that in can be moved as described?
The shaft has an helical gear, which means it will create an axial force. In which direction is that force (I'm not sure which direction rotates the engine) towards the front of the gearbox or the rear?

I look at the exploded view, pictures from the workshop manual, and to the gearbox (even though closed...) and I don't notice any mechanical retaining system for the axial movement of this shaft...

The mechanic seems to in the dark as well...
I'm getting desperate with the situation...In the last days he already assembled and disassembled the bike a couple of times...
He was already talking about splitting the gearbox, but if what I described above is normal maybe it would not be necessary to do it...The way things have been going I might get into more trouble...

I know it is not the best time for questions, once everybody wants to be in peace and enjoy Xmas (MERRY XMAS FOR ALL, BY THE WAY...), but if you can give some light here (please Pete) it will be highly appreciated.

Merry Christmas!

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There is, or should be, no axial play in the input shaft. The shoulder on the shaft, (Where the #1 pointer is pointing in the diagram.) is pulled up tightly against the bearing by the clamping force exerted by torquing down the peg nut on the front of the shaft which acts on the hub clamping it down with the bearing sandwiched in between. If the shaft is moving longitudinally then when the nut is being tightened down something must be stopping the bearing being clamped thusly.

Since the peg nut was previously loose it will of allowed the hub to move on the shaft, (Hence the original leak I’d think.) and the splines of either the shaft or the hub may of been damaged meaning that when the nut is tightened the bearing isn’t clamped and the shaft will be able to move fore and aft as the end thrust imposed by the primary gear acts upon in under load and on the over-run. When this happens the position of the primary gear will also move and therefore its relationship with other components in the box does as well.

Because the selector drum is in the way in the picture above you can’t see what the primary gear is in proximity to but if there is something close enough the primary gear will of started chewing through it like a milling cutter which might explain the noise.

The other possibility is that because the hub isn’t far enough onto the shaft when it moves forward it may rub on the clutch pressure plate when the clutch is not engaged but I wouldn’t expect this to make a noise as at that point the two components aren’t moving in relation to one another.

I’ll have to go and have a squizz at the parts book to see what sort of bearing is at the back of the input shaft. I think it’s a needle roller but I can’t remember. If the box has to come apart your bloke will need the box splitting tools to do so or will have to make some. If you try to just pry the two halves of the box case apart you will fuck the mating surfaces and it will leak when it is put back together.

Actually looking at the picture of the hub I can see that it isn’t seated properly. When the hub is seated and the nut tightened down the threads on the shaft should sit just proud of the surface of the nut. You can see in that pic they are slightly recessed. The shaft is not immobilised longitudinally.

Thank you for the feedback Pete.
I understand what you mean. That should be at least a couple of threads visible...
But I was there when he assembled the new o-ring and seal, and he really has tightened it hard...Never the less, after tightened, with a couple of mallet taps the shaft slipped in....

I made the sketch below showing what seems to be to me (by looking at these exploded views) the fit of both ends of this shaft in the gearbox housing. If this is right, the gap "G1" could allow the shaft to slide some mm in, or?....Unless the gap "G2" doesn't exists on the rear...
But then, how is it possible that the axle moves axially?

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The shaft end float, which should be zero, is controlled by the shaft being pulled up against the bearing inner race. That is done by the nut being tightened. The gaps ‘G1’ and ‘G2’ are self setting if the hub is pulled up against the front support bearing race. What is happening with your hub is that something is preventing that from happening and the obvious culprit, as evidenced by the incorrect positioning of the tightened nut, is that the spines on either the hub or the shaft are damaged and preventing the hub being drawn into contact with the inner race so under load the shaft is moving fore and aft under the force exerted by the helical cut of the gears.

I can see what you are thinking, that perhaps the bearing is moving in the case? There are two reasons I don’t think this is likely. Firstly, if the axial loadings were going to be great enough to make it likely they would have used a retainer plate on the bearing as they used to on the older five speed boxes. They didn’t and in twenty years I’ve never come across or even heard of a bearing ‘Walking’ in the case of a ‘Neuovo Six Speed’ (EDIT. THERE IS NO RETAINER PLATE LIKE THE EARLIER BOXES BUT ON CHECKING THE PARTS LIST THE INPUT SHAFT BEARING IS RETAINED BY THREE BUTTON HEAD SCREWS. THEREFORE IT CAN’T BE WALKING IN THE CASE. PARTS #4 BELOW.)

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Secondly, as I keep stating, the reason the shaft is moving is right there, staring me in the face! The nut, no matter how accurately tightened it is, isn’t seating the hub up against the bearing and the fore and aft movement is caused by the shaft sliding back and forth in the inner race of the bearing.

Things most likely to cause and allow that are.

1.) Spline damage to the splines of the hub or the shaft.

2.) Thread damage to the threads of either the shaft or, more likely seeing as it was loose and is the ‘Sacrificial’ part, the nut.

I’d suggest pulling the hub and examining the splines but also, with the hub off, installing the nut and making sure it will cleanly screw down on the threads until they do sit proud of the top of the nut. It could simply be the nut jamming on the threads of the shaft due to the nut threads being damaged/worn/eroded by having been chattering about when it was loose. If there is any doubt? Fit a new nut.

Hi Pete,

You are right...I missed those three bolts. That's for sure what keeps the shaft in position axially. I could not believe that a shaft with an helical gear receiving the torque from the engine directly would only be held in place by bearing interfearence fit...

You see, this guy made a big mistake....
When he was assembling the gearbox to the engine he felt resistance, and decided to make a test.
He turned the crankshaft, and because the output shaft of the gearbox was turning as well he assumed the hub was correctly positioned and forced the closing of the clutch bell tightening all the flange bolts...
But the small plate that receives the thrust rod was out of place, and was making pressure against the hub. He was only able to close the gap because the hub shaft was compressing the clutch springs. Could that have loosen the bolts? One might think that those three bolts should be able to sustain that load (the slave cylinder is held by three small bolts too), but that must have caused the problem because the bike didn't had it before...and the shaft has that axial play now...

When we installed the new o-ring we checked the shaft splines and the hub and all looked normal. We could see as well the bearing inner race face. The nut was tighten, and well tigthen, trying to align the nut grooves with the next tabs from the washer. I guess this shaft came a bit shorter

I took a look at some gearboxes on the net, and in the case below there seems to be some thread showing (but not much...).
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So the axial movement seems to be the cause for that grinding sound, resulting from that helical gear chewing other parts.

At this point, having that axle movement issue, all those shavings circulating in the bearings and gears, and some chewed parts, I am considering to buy a second hand gearbox, which I can find in the net. I came across one that is looking good and has the marking below, exactly like mine. They mention the Manufacturer Nr. 05200531.
I believe this one would fit my bike in terms dimensions and gear ratios, right Pete?

Matias wrote:

You see, this guy made a big mistake....
When he was assembling the gearbox to the engine he felt resistance, and decided to make a test.
He turned the crankshaft, and because the output shaft of the gearbox was turning as well he assumed the hub was correctly positioned and forced the closing of the clutch bell tightening all the flange bolts...
But the small plate that receives the thrust rod was out of place, and was making pressure against the hub. He was only able to close the gap because the hub shaft was compressing the clutch springs. Could that have loosen the bolts? One might think that those three bolts should be able to sustain that load (the slave cylinder is held by three small bolts too), but that must have caused the problem because the bike didn't had it before...and the shaft has that axial play now...

Pick the bike up and run, do not walk, run, away from this place and let’s see if we can fix it without fucking anything else up!

Jesus!

Fucking!

Wept!

Absolutely Pete...
Since I bought the bike in 2011 it was the first time I took it to the workshop for a repair instead of doing it myself...I already regreted it...
I knew I had to take the bike apart and didn't had the necessary means for that, so I went for that option.
The odds were good...The guy worked for the MG dealer in Lisbon (where I bought the bike), trainning certificates still hanging on the wall...But he really messed-up...this is a basic rule...we say in Portugal "the material is allways right"...If it doesn't want to go something must be wrong....
But at least he assumed he messed-up.
Anyway, I would do like you say if I didn't had the bike parts spreaded around the workshop like you can see in one picture of this thread.
I guess I will have to let him try again, with me looking over his shoulder...
Do you think that gearbox I mentioned will suit my bike?

Do you know if he even assembled the clutch right? Does he understand about aligning the pressure plate in the flywheel? How did he align the intermediate plate? Would you trust him to install the rear main seal properly?

There may be many things wrong with your bike now. The axial movement in the input shaft has one cause and one cause alone. My guess is if you get the hub to seat as it should everything there will be, if not fine, then at least perfectly serviceable. At this point I certainly wouldn’t be looking at buying another gearbox. Especially if we don’t know whether the clutch and mainseal have been done right.

A Guzzi is one of the simplest things in the world to work on! Really. Just because all the bits have been pushed back into place roughly where they came from doesn’t mean it’s going to work! Everybody makes mistakes but this is first, or at best second year apprentice stuff……….

He centred the plates using the clutch hub.
He took some pictures as he was getting along. He removed the main bearing flange using an extraction tool, and assembled the seal in a press with a metal plate over it. Seemed OK to me...
I think engine and clutch are OK. It was engaging and disengaging normally. Hell only went loose after going uphill and openning the gas, because that pushed the clutch shaft backwards.

Now, with all that gearbox went through I don't trust it anymore.
I have some options at around 500€...more and less a set o tyres...What is holding me back a little is that even when they look good on the outside you don't really know about the inside, right?

Looking at your bike in the pic above, HOW did the guy get that gearbox out of the frame?
Seems the pipes, TB's & airbox are still in place. May have something to do with gearbox issues.

He removed the swing arm, released the engine from the frame, released the throotle-bodies from the airbox, and lifted the frame slightly from the back with a small crane.
I was there but don't have pic of that stage, just this intermediate one.
As we were deciding what to do with the gearbox we removed the bike from the elevator.
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I was just wondering, I have always had to take engin & gearbox off as a unit cocked on angle cause frame wraps under back of gearbox. All good.

That's what he should have done Steve....he would have a better control over the operation....

Merry Christmas all !

Matias wrote:

He centred the plates using the clutch hub.
He took some pictures as he was getting along. He removed the main bearing flange using an extraction tool, and assembled the seal in a press with a metal plate over it. Seemed OK to me...
I think engine and clutch are OK. It was engaging and disengaging normally. Hell only went loose after going uphill and openning the gas, because that pushed the clutch shaft backwards.

Now, with all that gearbox went through I don't trust it anymore.
I have some options at around 500€...more and less a set o tyres...What is holding me back a little is that even when they look good on the outside you don't really know about the inside, right?

Sorry, a bloke has to sleep sometimes…….

There are so many things that worry me here. OK, so he removed the rear main flange to do the seal? Fair enough, but was he aware that the flange is not symmetrical and can only be installed one way when he stuck it back on? Also, while walking around the shop with it did he make absolutely certain that the oil feed dowel for the rear cam bearing that also acts as the locator pin for the actual bearing in the flange didn’t drop out? Either of these mistakes will cause the rear main to seize when the oil warms up.

And you say he centred the plates with the clutch hub? OK, that’s fine, but did he compress the clutch springs using a bolt, washer and nut to enable full engagement of the intermediate plate in the splines before installing the ring gear? And is he aware that the clutch friction plates only fit one way? With the raised flange of the plate centres facing rearwards?

As I said, at this moment I still don’t think you need another gearbox. Drain the oil out of yours and see if it comes out silver. If it does? OK, buy another box but for now I’d concentrate on getting the hub to seat properly on the splines. How did you hold the clutch hub on the input shaft to tighten the nut?

.

There are very few -- the number zero comes to mind -- moto-techs of any brand, much less in the subculture of Moto Guzzis, who know as much as Pete, Lord Roper; share it so generously at the expense of his personal time; and convey it at long distance with such clarity that a know-nothing and do-less such as I am can even think I understand what is happening.

You, Pete, are a first-class Christmas gift to all Guzzisti.  Bravi!

Oh, and Merry Christmas to you, Pete, Jude, and all who you hold dear ...  and to all on this great forum.

Bill

Well said Bill. This forum is a great place, largely because of Pete's generosity. And of course, Pete "Street" plays no small part as well.