Rear drive box V65...VERY tight pinion shaft

[JohnCantor]

I’m new to this forum, thanks for letting me join.

I am in the middle of a rear drive gearbox rebuild on my V65 GT, and I’m a bit puzzled by a few things.

I had oil coating the disc brake, so decided to replace the big seal.  It stripped out nicely and looks very clean inside and bevels nicely polished. However, the small pinion had over 1/2mm end play, so I am very glad that I have stripped it.

I tried to push the pinion shaft out (having removed the circlip), but it was VERY tight.  Eventually, with full force on my vice, there was a little ‘bang’ as it moved, and there-on it pressed out.  The shaft is in perfect condition, and I measured it with my old micrometer. I would estimate it to be 0.3 thou bigger than 20mm.  The bearing is thick-walled, so tolerance is quite critical.    The Breva manual says ‘remove pinion’.  Should this actually be a nice slip fit?  Why was mine so tight?   Surely not an undersized (SKF) bearing? Possibly an oversized shaft?   Problem here is that the only way of getting the shaft out is to push on (through) the taper bearing….  It just feels very wrong!     I’m thinking of easing the smaller bearing end down.  Its less of a problem for the pinion end because this bearing can be wound on and off using a bearing puller.   Anyone else had this problem?     There is no evidence of locktite being used.  Is my bike the only one with this particular problem?   Any thoughts welcome.  I have yet to grapple with the challenge of shimming it up….. It will be a slow process.   Good job that I like a challenge!

[oldbike54]

 Bump , where did this thread go ?

 Ah , there it is , I moved it to the main board and lost it 

 Welcome to WG John .

 Dusty

[JohnCantor]

A quick update on my own post.
I decided to pull on and off the old bearing inner sleeves to see how much force is needed.  I'm gearing myself up to fit the new ones and check/set the pre-load.  I am being VERY cautions. 
Anyhow, both bearings are actually about right on the shaft.  They moved with medium force with a puller.   The one that was VERY tight, is now about right.

So, I am no longer puzzled about shaft/bearing dimensions, but remain a bit puzzled that it had so much 'grip' in the first place.

[oldbike54]

 Kinda surprised no one has offered an opinion or advice on this .


 Dusty

[Kiwi_Roy]

Welcome to the forum, I don't think too many have experience with setting the gear clearances.
I have seen several write-ups on how to do it.

[JohnCantor]

I guess its too expensive/risky to these days. 

My first bike (in 1970!!) was a 1937 triumph singe. I paid £5 for it, and I could afford to take eveything to bits and learn the hard way. If I messed something up, there was usually some way around it.  If I were to mess up with my Guzzi rear drive....  it will be costly in parts, so its not sensible to experiment.    There is always a learning curve, and that often involves costly damage.

It makes sense to let experts do this sort of work.    I'm not particularly sensible!

[guzzisteve]

You may want to check for a drilling to add in the lubrication of pinions on the smallblock. Might be in Guzziology, don't know but I drilled a bunch in the 80-90's. Use the exact same bearing size of high quality AND the same shims between them, new locktab on nut, torqued to spec. The box is shimmed put together but off the swingarm. Use spacers under the 4 nuts, cover on back has to be torqued also, it holds the ring gear hub.  When assembled you install a puller that will rotate w/gear hub and pull slightly on it away from pinion. This is the gap or play that you check with blueing on teeth. If all you do is rehab it w/new bearings & seals, same shims & gaskets you'll be fine.
If it didn't want to come apart it most likely doesn't have the oil drilling done.  I have a drawing here in a book somewhere in a box in the garage. Haven't looked at it in over 20yrs. I'd look into it.

[JohnCantor]

Many thanks Steve.  I guess its a drilling that is mentioned in a post/bog some years back, but I think mine was made after the mods were done (mine is 1991).  So I think mine is already drilled.  Mine has a 20mm bore and a 25mm bore bearing. older ones are 2 x 20mm i think. 
I was thinking I might need new shims with new bearings, but nice to hear that you think it might be OK just with new bearings.
I had read about the need to 'pull' on the shaft when checking the mesh.   I have in the past coated the gears using a permanent marker, instead of using engineers blue.  Do you think I should get some proper blue?   Gear faces look really good, so with luck, they will be OK.  That said, it would be awful to get it all back, only to find it a bit noisy, so I will spend time getting it as good as I can
Thanks for your thought.   

[JohnCantor]

I thought I would give a bit of update here.  It might be useful for others with small block models.

The reason I took mine apart was because of an oil leak.  However, I discovered that the pinion (the small shaft) bearings had a lot of play.  Having changed the 2 taper roller bearings, the end float seems perfect now, with the original shims.... all good, and I'm glad I did it, though it's NOT a job for the un-experienced!!

I tend to think that I would have ruined my bevel gears if I had kept riding it for a few more k's miles with sloppy pinion bearings, so this detail is important to look into.

Given that I think my bike is low-mileage, it seems likely that my bearings have suffered lack of oil.   It looks like I have the drilling as mentioned by Guzzisteve (Thanks Steve) , BUT my shim was not swapped around like I have read about on a Guzzi bulletin (see pic amdf link below)

There is lots of good info about.  This from Peter Roper is very informative  https://www.thisoldtractor.com/guzzitech.dk/gb_en_complex-technical_bevel-box.htm      I also came across bulletin about flipping and re-positioning the shim file:///G:/My%20Drive/Motorbikes/Guzzi/moto_guzzi_technical_bulletin_100%20rear%20drive%20mods.pdf

I'm not exactly sure how much better moving the shim will be, but it looks plausible it might help. 

I have yetl to check the gear meshing, but even by just changing the pinion bearings, I think I have saved my bevels from an early death!





Luckily, I am in no hurry to finish.... its a long drawn-out process!

[John A]

It makes a little reservoir so it might help a bunch.  I’m sure the reasons nobody posted is because nobody knew. We don’t have an Oracle to consult since Roper has left the building. Thanks for the update

[SED]

Sounds like a good fix.  I've been into the bevel box on my Monza but didn't replace the pinion bearings so didn't have anything to post.  I'm glad you kept at it and posted the fix for us. 

Do you think it was just corrosion causing the stick?

[JohnCantor]

Hi SED,  I'm still a bit puzzled by the tightness of the inner race on the pinion shaft (the threaded end).    The shaft had no corrosion.  See picture from when I got it out. The red line is the bit that was very tight.  it was partly shinny black.     

I have now spent 5 mins with very fine emery on the area marked, and pulled the old bearing on and off a few times. Now its a nice tight fit rather than very tight.

There is an old saying..... 'for important decisions... sleep on it'.   I am applying that here, and luckily I am in no hurry.... there are many months before I intend to get the bike back on the road!!

[tris]

How about this for a hypothesis - it cold welded together?

Many MANY years ago I was taught how to "ring" slip gauges together

I was also taught never to leave them rung together as the surfaces were so flat that the molecules could transfer between the 2 slips effectively cold welding themselves to each other

Maybe you just had a perfect storm and the surfaces were good enough that they just "Stuck"?

[JohnCantor]

I think you could be right.  If only a few very tiny high-force contact points 'weld' then it could explain the grip.  It could also be high-points, on a microscopic level, interlocking.... who knows.