Modern Vespa

So a friends Non Vietnamese VBB that used to run fine, ended up with the clutch woodruff key jammed in the gears about a month after he changed the clutch. It must have been sitting in there a while but he came to a skidding halt. I got the motor and tore it apart to find out what it was. Rebuilt the motor with a new shift cross, seals, gaskets and fired it up. It had this bang, bang, bang noise coming out of it. Tore it all apart again. Scratched my head a bunch and here's where I'm at.

-Removed and reinstalled the old shift cross. No change in the sound
-inspected all the teeth of the gears. Nothing nicked or broken.
-noticed a small nick on the inside of third gear. He jammed in third and slid to a stop.
-inspected all the teeth on the primary drive. Can't see anything
-Inspected all the teeth on the cush drive. Dont see anything.
-Removed and reinstalled the clutch with a new woodruff key.
-Removed the clutch cover and pressure plate.
-Removed the rear tire and hub
-Removed the head, cylinder and exhaust during initial rebuild. New piston rings only.
-Kickstart cog inspected. Nothing and reinstalled. Makes the noise even if the kickstart lever is engaged.
-side loaded the crank by pushing on it from the flyside.

After all that and probably more that I forgot, it still makes this banging noise. Watch this video and you'll hear it. Its a little faster than once a second. It used to go away in neutral but now its all the time in every gear.

Anyone ever come across this one?

Sounds like gearbox. Does the tapping noise stop if you pull the clutch in? How about when holding in clutch and in gear?

So the problem was definitely gears. Jack you nailed it and sorry I didn't respond. I had to leave for 3 weeks for work so the project sat. Once it was in a running stage, I ran it and squeezed the clutch and the noise went away no matter what gear it was in. It didn't have a wheel installed so I couldn't roll rear it.

Interestingly enough though, there were no broken teeth. I had 4 sets of eyes look the gear cluster and the primary and other than a small indent, nothing was broken.

The owner priced out gears and said screw it and decided to spend money on everything else (rear axle, rear seal, rear bearing, selector side axle bearing, new kickstart cog, Cush drive rebuild). He's going to live with the clicking until something breaks or it goes away.

19 secs into that video.. is that the g'box drain hole?

Yes

Reckon that's it

Ok so I went back and forth the last few months. I got two different cush drives and had more people look at parts and no one could find anything wrong.

Eventually I got the idea to spin the rear axle with a drill so I could watch the gear cluster since the cases were open. I narrowed down the noise to a bad second gear and eventually right to the general problem area. Its hard to see but theres a small crack forming in the gear tooth and that was all it took to make that noise.

Massimo hooked me up with a new gear and I installed it and confirmed with the drill spinning that the noise went away.

The owner said lets have some fun and for Christmas bought the two port bolt on Pinasco 177 kit, the pinasco clutch spring/ cups pack, a 24/24 carb and a SIP Road 2.0. We opened up the airbox for the 24/24 carb but right now its running great with the stock points flywheel @ 18*BTDC. I started the main jet at a 110 and it ran great. Kept going up in points to a 128 and the owner says he feels no difference wide open. Will confirm with a CHT soon.

So that wraps up my saga. Glad to finally have this head scratcher behind me.

You're so lucky you got it on time, Malcolm. A friend of mine wasn't with his PX200. A tooth from the "christmas tree" broke (3rd gear), got wedged between the cases and the 1st gear and cracked his cases. Thankfully the pieces fell when he reached home and we were able to weld them back...

Hot damn that's some carnage! Glad you were able to save those cases.

This whole experience has been an interesting one. Next time I told this guy to just pay me to fix his stuff next time.

For now the old gear is going on my wall of shame next to the other bizarre motors I've worked on.

Good sleuthing. Now I know what to look for next time I crack the yellow rocket open. It has the same click.

So what was the final jetting on the project MJ? I have a slightly used Pinasco 2-port kit that I traded for and was planning on using it on the 66 Sprint with a 20/20 carb, rather than the 20/17 that came with it.

So we went with a 24/24, air box matched to the carb. No inlet porting. Stock starter and idle jets, air filter heart drilled. Started with a 110 main jet and kept increasing it to see if there came a point where it was too rich. Ran out of jets with a 128 installed So, I'm making the owner break in the motor and then I'll do some CHT runs to figure out the best main jet for you.

Wow nice find

wow. good thing to be aware of in the future! those things are so chunky I didn't think an epic failure like that was possible.

Have a similar sound here.
Went on an uphill WOT plug chop run. Shifted backwards! Dyslectic style.

Opened the cases. Very small piece of the cruciform found. Not enough to make this light sleigh-bell rattling sound.

All gear teeth are perfect. Primary gear teeth perfect. What am I missing?
Can enough smashed cush springs make this sound?

About to just replace the cruciform and see how that goes. Any advice appreciated.

I've had one where the cush had smoked the springs and sheared some bits and had a funny sound when running. so give it a shake and see? this was just general neglect.

also had one break a cross from a missed shift and somehow wax the cush bearing. don't know if it was from shock load due to everything stopping quickly or what. but same thing, all the gears and teeth checked out fine, just had noise while running. chased my ass on that one real good.

iirc, you're running a pretty stout clutch so I wouldn't worry on that side. but a damaged or loose basket can make some real interesting noises.

good luck!

Ray,

Still have the cases open? Spin the axle with a drill and see if you can narrow down the problem area.

I once had a cruciform break and jam the gears solid. When it was put back together it made a constant knocking sound but otherwise ran fine. It turned out to be a bent drive shaft.

hahah!
Oh man - have been there.
What a gut wrenching feeling to turn the shifter the wrong way.
Like MJ's spin it with a drill.
See if you can create the sound.
I'll keep that one for my own diagnosis the next time I find myself there.
Perhaps you can also spin the clutch so it spins the xmas tree - see if you can find Rudolf.
Keep us posted.

I once found a bit of metal wedged between the gears. Pretty sure it was soo wedged that it was acknowledged & left there, never caused a problem... but i have the odd issue with metal components


No wonder the clutch was slipping!

Crank was also slipping!

As was the flywheel

I do. Gears and clutch are out. I'll pick up a new cruciform and do your your drill test with everything together.
Thanks!

Thanks!
I have the "little brother" version of the BGM superstrong clutch, rated up to 15hp. This may not take distracted backward-shifters into account. Going to take a better look before doing MJ's test.

Gearbox will click if it needs shimming. Check the endplay.

It's a thing.
Fuel tap too.

Or if you forget the thrust washer under the clutch, especially when you roll it backwards.

Okay, replaced the criciform, installed the gears, took the clutch apart no issues, spun the primary with a drill to see if I could get a rattle. No sound.

Went to do MJRally's spin test with a non-impact drill and the nut came loose with maybe 10ft lbs.
Bearing fail?

*Cotter pin was ok. Removed it to fit the drill.

Ray, pull the clutch so there's not too much drag and spin the drill so the nut tightens on itself. You don't need to get the drill rip roaring for the noise to start showing itself. Since there's just the drag from the Cush drive, youre not gonna damage anything on the rear axle. Worst thing is you might need to impact it the nut off when you're done.

Worked just fine for me and no problems after the fact.

Okay, found the issue.
Bearing was shot. Abrasion marks on the face and inside the inner race. Bearing grinds while rotated by finger. Axle slides freely in the bearing. No clue as to how that could happen.

Tried to maybe find a speck of cruciform by blowing brake cleaner through it into a white styrofoam box
I'm getting old.

MJ spin test like butter with a new steel-sealed bearing and FA crankshaft (comes with a lusso nut end*).
*affords one the opportunity to toss another castle nut

Closing the cases tomorrow and giving it a road spin.

Following up.

So I took it for a spin. The rattle was gone, but there remained a light but constant click sound in 1st and second. Rode it for a few months no other issues.

Opened it up again. Gears were shimmed correctly. Two springs in the primary were broken and the bearing was shot.

When rotating(new bearing) with the smaller half off and engine facing down in a vice, one tooth on the cluster would hang-up slightly against the 1st gear cog. All teeth were in perfect shape, so I wrote it off to being out of tolerance with the weight of the driveshaft against it and the shafts not being seated in the small half. Still, it was that one same tooth that hung

Rode again with rebuilt primary and new bearing. Still clicking!
Clicks in 1st, nothing in neutral, less in 2nd, barely in 3rd, nothing in 4th.
Clutch pulled no difference.

Any suggestions?
Just replace the cluster? Replace the shaft as well?
Transmission took about as hard a hit as possible. Shifted backwards, 3rd to 2nd WOT uphill

Can you post a vid or a soundclip?

Sure.
In the middle I'm rolling in neutral with the clutch pulled.

https://www.youtube.com/shorts/5L-nsCD8TYg

I can't hear anything too specific. Can you kill the ignition and coast while recording?

Now that I hear it on my laptop, I see what you mean. Played on my phone through earbuds the clicks are pretty clear, especially during the first and last few seconds.

I'll post another tomorrow, coasting.

Ordered a cush drive and spindle from Scooter Mercado. Unfortunately, the only supplier of the 12-16-20-25 is India.

Ray - I can hear it.
Any a chance the kick start gear is involved/damaged?
Is the kick start lever in any way lower by a hair than it should be?
Just sounds like the tips of the gear might be engaging in some way.

I think you nailed it, Ned.

Replaced the kick start gear with a PX one I had on the shelf after this first happened. Didn't realize the 12 tooth P kick start gears aren't the same(?).

Video below:
Rolling off in 2nd downhill, then 3rd, 2nd, neutral, 1st, then back to neutral.
The clicks trail off into neutral, especially at the end.

https://www.youtube.com/shorts/3btBmLXwIqY

Yeah can hear the clipping noise…

Your gearbox oil should be very glittery now.

Good you have a lead on the problem

New pocket video posted below.
Thanks so much for the suggestion. Hearing it now says a lot.
If it's just an incorrect kickstart gear I'd be really happy.

*There's some distortion with a helicopter overhead. The clicks are also not nearly as loud by ear. No clicks on the bench using a drill to spin gearing, 2 separate times.

Blind squirrel:nut
Maybe someone can comment on your insight on p gear?

Will be interested to hear what the root cause of it engaging if it turns out to be the gear.

Thanks.
Just drained it. No glitter. Nothing magnetic in it either.