Modern Vespa

Hey,
I have a '63 VBN that was modified with 10" wheels by a previous owner. I'd like to put 8" wheels back on it and I'm wondering what I'll need. I know I will need new rims, tyres, drums, shoes and rear hub. Looks like SIP has most everything. However, I can't figure out if I need a new fork. The clearance on the fender is tight with the wheel and with the leg shield. Is there a way to tell if the current fork will fit an 8" hub by just looking at it..without removing it completely? If I DO need a new fork, would Bajaj be good enough or should I look at getting something of better quality. I'm just a mellow weekend rider but I want it to be safe obviously. Pics are included. Thanks

Welcome to MV, and thanks for the beautiful pics! I don't have any useful input for you on the tire change, but someone who does will probably be along shortly.

It looks like you would just need a 8 inch wheel (rims), tube and tire on the front. Everything looks to be already there, but the real experts will be along soon enough to confirm. Need some pics of the back. Good luck.

Awesome. Thanks for the reply. That would be great if it's only rims/tires. We'll see….

Your gearing will need help

Speedo gear

I never understood why people objected so strongly to how 10" wheels looked on a bike that came with 8's…I could barely tell.

But I finally see it here. The fork angle looks wrong and the mudguard looks out of place.

On the front that's just an adapter rim from 8" to 10" like this: https://www.scootermercato.com/Scooter-Parts/Rims/SUPERCONV_2

And I'll bet a dollar the reason they did it is the original motor was replaced w/ a 10" motor. Motor pictures, please including serial # on swingarm?

You could change the motor over to 8" with some gearing work to compensate plus the right brake backing plate, a few random parts parts and an 8" hub, either VNB like your frame had originally or Super style like your front hub. That's the real mystery here, why an 8" Super hub on a VNB? Anything ELSE we should know about this bike?

If it IS a 10" motor in back, you might be better off doing a proper 10" conversion in front just for the bigger brakes if you dont wanna mess w/ the engine and the gearing. Much easier to convert the front properly to 10" and cheaper. Look here, starting on page two for details. Unpainting a scooter

Good point and eights ARE fabulous! But tens can work, lots of ppl have done it and happily ever after. I do think a Super pulls it off better though, but it may be I am just biased.

Thanks so much for the detailed reply. I know the previous owner put a 150cc 64' Piaggio engine in it that was rebuilt by Scooter Bottega many years ago. However, the 10" wheels were done before he owned the scooter. I'll try to get a serial # later. It feels funky in the front when riding so I figured it's all due to the sloppy 10" conversion.

As far as the fork is concerned all you need is the axle for the 8" wheel. Then you'll need the rims, tire, brake shoes, nuts to hold the wheel on and that's all.

I just did it on my Allstate thread. It's super simple.

Sweet. Nice looking bike!

an 8" super fork with a SEA conversion 10" wheel... hmm. okay.

and then I saw the PX center mat...

might not be ALL bad, but you definitely gots shenanigans cooking.

ike voodoo said, what's up with the motor? that might be a big factor in tire size and why it's on 10's

however, it may have all been swapped to super stuff and just come down to snapping on the right rims.

The previous owner put a 150cc 64' GL motor in it that was rebuilt by Scooter Bottega many years ago. However, the 10" wheels were done before he owned the scooter. I agree that there are some suspicious features. Hoping it's not a viet-bodge but not ruling it out either. I just want to get it as safe and reliable as possible. Aside from the funky front wheel it runs pretty well.

what's the rear wheel/hub look like?

I have seen photos of 8" bikes running a 10" wheel on the back and an 8" rim with a larger tire on the front. It didn't look odd in photos…no idea how it would feel to ride one.

As said... the front is simply a 8"-10" conversion rim... just put on 8" & all done.
I have used conversation rims a couple of times, so keep them, as they're hard to get

"I have used conversation rims a couple of times, so keep them, as they're hard to get"
But they never shut up.

Here's the rear wheel.

standard 10, so no big deal to convert it back to 8.

basically, you could scoop the 8" stuff for the back-- it'll be the "correct" 4-lug stuff and that's all easy to get: backing plate, brakes, hub, drum, rim, lug nuts/washers and a seal.

up front, you just need an 8" super rim

but, now herein lies your problem: now you have two different rims front and rear-- which you have now, so whatever. but also you'll have a super front fork and not the "correct" style. but if that doesn't bother you, then go nuts amigo.

for a little more dough, you could hunt down a rear super 8" backplate, brakes and hub and rim and have matching rims front and back at least.

either way I'd take a good long look at that front fork before moving forward.

Thanks man. So in theory, could I also resolve the mismatch by replacing the front fork with a vbb fork and getting the correct vbb hub/wheel setup? SIP sells a Bajaj vbb fork, though I'm not sure what the consensus is on Bajaj quality. If it's worth it….

Also, would I still need to mess with the gearing, given its a '64 GL 150 engine?

yeah, swapping the fork would resolve the mismatch on wheels and also give you the correct appearing front end.

the Bajaj stuff is "okay" but should be gone through. you could hunt around and pick up some used good quality stuff to rebuild for a little less money, but a little more leg work. depends on your timeline and skill level.

the gearing most likely will need to be addressed. you might get away with just down gearing the clutch if possible, but to fix it right you'd have to change out the primary. which means getting into the motor... and that's a whole basket full of snakes.

Ok, cool. I'm gonna look into the cost of this conversion. If I pull the trigger I'll update the post. Thanks for your help.

word. use the search function there's a ton of threads about Bajaj forks and rebuilding standard stuff that can be helpful.

don't hesitate to ask questions here, either. there's a whole lot of knowledge floating around. and a bunch of us have parts too!

Before I commit to converting to 8s. Just how much of a pain is it to correct the gearing in the engine? Not sure I understand how to adjust the clutch for workaround if possible. But if I DID have to get into the gearbox would I have to take the engine out completely? From what I see online, it doesn't look easy! Maybe I should just stick w the 10s!

It's not bad at all on a large frame scooter to change clutch cog if that's all the further you need to go. Pull rear tire, remove clutch cover, remove center nut. An hour if you've never done it, maybe 30 minutes after that. If you need to replace both gears you have to pull motor and split case. Would be a good time to see what you actually have for a clutch, gear and center nut. Old style is a castle nut with cotter pin. New style is a locking nut, most prefer new style nut. Then we can help with a new gear.


I've personally never converted from an 8" to 10", not sure if you can get away with just a higher tooth count clutch cog. You're trying to get closer to a 1:1 ratio with larger gear. I would suspect part will depend on you use and speeds you want to achieve.


Parts people are talking about

https://www.sip-scootershop.com/en/search/Clutch%20cog?model=eyJzY29vdGVyVHlwZSI6IntcIm5hbWVcIjpcIlZlc3BhIDEyNS8xNTAvUmFsbHkgJzU3LVwiLFwic2x1Z1wiOlwiVDZcIn0iLCJwcm9kdWNlciI6IntcImd1aWRcIjpcImI5NjIzNTQ1LWRiMjQtNGE2My05Y2NhLTExNTE4N2FhZmZkZFwiLFwiaWRcIjo2LFwicHJvZHVjZXJuYW1lXCI6XCJWRVNQQVwifSIsIm1vZGVsIjoie1wibmFtZVwiOlwiMTUwIEdMIDE1MCBjY20gMlQgQUMgJzYyLSc2NCBWTEExVFwiLFwibW9kZWxfbnVtYmVyXCI6Nzc5fSJ9&dim=2&page=2

Cool. Thanks for the info. Replacing the clutch cog is something I could handle. Opening up the engine...that seems like something I'd REALLY like to avoid! I don't care much about fully maximizing performance. I mainly want to avoid making a change that will potentially mess up the bike...like forcing too much rpms on the 8" wheels etc.

Just from personal experience, I converted a PX150 engine to put in my UK Douglas 152l2 (VNA1T), so it would work wit the original 8" wheels. I changed the primary drive as per the Scooterhelp gearing calculator and it works really well. I ended up using a Malossi primary drive.

https://www.scooterhelp.com/tuning/vespa.gear.calc.html

Is that a CRACK next to the motor VIN?

Not trying to be a Debbie Downer.

Probably casting marks...

Thanks for looking out but I don't think that's a crack. I see other Piaggio engines have that same line.

Awesome. Good to know. I'll probably end up doing the same. Thanks

I converted a 10" LML (Stella/Star) motor to 8" for my VBB. Sadly, when I went to pull a link for the SIP 10"->8" conversion kit, it's discontinued. You can still get the parts, it looks like, but you'd have to mix n' match them yourself. The axle is the only truly custom bit, and they still seem to have it, though.

For the front fork, I have one of the Bajaj 8" forks and eventually, the only piece it I kept was the fork itself. You're better off either finding a used/NOS fork or just buying the tube and picking up the other parts separately.

And, yeah, the PX floormat on that thing is a baaaad sign. Can you get some pictures of the inside of the tank cavity and up into the tunnel? There's a non-zero chance that scooter is actually multiple scooters, welded into one.