Modern Vespa

Hello, I'm in the process of rebuilding a P125x motor. I installed the new crank, replaced seals and bearings and reassembled.

The cush drive is now binding. After examining it closely, I can't see where it would be binding. I then split the cases again and took the cush drive apart, cleaned and reassembled. It's still tight.

Any ideas?

Possibly the wrong size of needle bearings were installed on the shaft that slides through the middle of the cush gear assembly?

Hmmmm, you may be right.

Thank You!

watch the rivets on the case as another spot where something could drag - but you should be able to see witness marks if this is the case.

Well, it's not the needle bearings. I tried it without, and it still binds. It doesn't bind until I lock the spindle all of the way in.

Also, there aren'y any witness marks and I can't hear anything rubbing, coming from a deaf man.

bad bearing? Does it bind when out of the case, or only when installed in the case & meshing with gears?

The bearing seems fine, it binds when the threaded end is pushed out of the case. It was spinning freely before the rebuild. It has to be something simple to someone other than me

The transmission isn't in the case any longer, so I could take that out of the equation.

can you post up some pics?

This is where it starts binding. It looks like the hole the spindle feeds through could use a little cleaning on the bottom photo

Is it the original input shaft and xmas tree to the engine?

Does it bind when you have the output shaft and gears in the case?

It has a new shifting cross, but not a new input shaft.

It still binds with the gear set in place.

The bearing center race is captured between the step on the shaft and the case when the nut is tightened. In your second pic, it looks like the face of the case where the race is clamped against has a circular recess in it. It should be flat. Maybe tightening the nut pulls the bearing in too far and the ball cage is contacting the case ?

It may be an optical illusion because it's pretty flat. Everything spins freely, until the shaft is moved home for the last 1/2".

Here's a few pics that hopefully will help. If anyone needs specific pics, let me know and I'll post them.

Some more:

The old me would fasten it all up and hope for it to "self clear", but I don't want to damage anything. I don't really want to throw parts at it, but I'm having a hell of a time seeing where it's binding.

Is the primary gear facing the correct side?

The machine while riding has never worked out for me. Could the shaft be bent? It's a puzzle for sure.

I believe so, I didn't take it apart. This is my first Vespa build, so my knowledge is limited.

Maybe that shaft is tweaked….maybe shoot & post a video of the issue

How does one upload video here?

Upload to Youtube, then post the link here

Sounds like the winner

I'd think if the gear was contacting the case it would be evident. What does 'binding' feel like ? It is 360 or intermittent ? Does the rotational orientation of the shaft matter ?

The binding is intermittent like something isn't straight. It gets tighter at the same point of rotation, but I see or hear no rubbing.

I think I may order a new shaft.

I didn't rebuild the cush drive so the drive gear isn't the culprit because it was smooth when I removed it.

A few short videos:

https://youtube.com/shorts/TuUAfxgdOkc?feature=share

https://youtube.com/shorts/BsWXcv-upXk?feature=share

https://youtube.com/shorts/9OpOf8chxGo?feature=share

https://youtube.com/shorts/bmLHJYzK9zs?feature=share


A pic down in the christmas tree

Shaft may be bent?? One side touches, gap on the other side...

Without the rollers in the end there'd be some play in the ball bearing so that would be hard to assess, no ? Do you have all the little needle rollers installed ? I don't see them in you pic.

If the shaft was bent the cluster still rotate true. But then with the shaft installed, the gear would contact the case in one spot. Should see on the case where it is touching. Probably wouldn't line up and enter the bush on the fly side case either.

Roll the shaft on a flat surface and see if the end wobbles around the axis. I don't see any way that shaft could get bent. From what I understand it was all fine when it came out.

I took the needles out while trying to figure this out.

One of the videos above shows the shaft rolling on the floor. It doesn't look bent, so who knows.

I bought a new shaft which took a while to receive. Unfortunately, it didn't fix the issue. I've taken this apart so many times that I have become an expert in assembly and disassembly, but I suck at fixing.

Any other advice someone can give me would be much appreciated.

Also the christmas tree that came with the engine is 25-20-16-12, and the tranny gears are 57-54-48-44. I see this isn't stock gearing, but is it acceptable?

Ok, I may have solved the problem. It was barely rubbing on the crank bearing retaining ring. I also noticed a tiny piece of the circlip retainer is broken off of the case. Do you think I should be real concerned about this? The pic below shows the spot vis the screwdriver tip.
I tapped in the bearing a little, and everything spins smoothly.

In that photo at least, one of the ends of the retaining ring is not in the groove. The missing bit should not be a problem. My 200 engine looks just like this. The bearing is held with 2 tabs with no retaining ring, even though there is a groove for it.

Edit: Actually, I'm not sure what I'm looking at. Something strange about the retaining ring groove. It's hard to see in your photo.

That's the wrong circlip. I would just buy the 2 tabs and use them. Glad you found the issue, was getting weird.

It may be an optical illusion. The retaining ring is inside it's groove, except the broken portion.

Thanks for the re-assurance about the case. Vintage Vespa knowledge is very limited here, but I like a challenge.

Thank's Jack, what are the tabs you recommended?

Looks like someone installed a PX EFL circlip into a P non-EFL engine case? You need to get a pair of the thick rectangular shaped P series bearing retaining tabs and a pair of the nut retaining tab washers. The primary gear is rubbing against that circlip. The retaining tabs will fix the problem.

Can you take another pic that isn't a blurry?

First of all, thank you for all of the help.

I think I found the correct tabs. This pic should be better, and I've included the tabs in place, hopefully.

You'll need those tabs, plus the thick plate steel rectangular retainers. They are about 1/4" thick. It goes in this order, bearing, thick retainer, steel locking tab, nut. Then once the nut is torqued, bend the tabs of the steel locking tab to press tight against the nut, to prevent turning. The short portion of the locking tab points up/towards the clutch; with the tab on the outer edge.

This is what it looks like on my '79 P200. No retaining ring when I took it apart. The tabs have thin locking tabs over them.

A picture is worth a thousand words