Modern Vespa

Hi there,

Long time lurker, first time poster here. I own an LML NV150 (I believe known as Star in the US market), otherwise an equivalent to PX150E.

As I'm putting to plan the mods I would like to perform to this scoot, it has developed an issue with the gearbox and/or clutch. It's slipping under load in 2nd and 3rd. While I find most describing the cause to this issue to be the cruciform, it feels different. I'm not disagreeing with the former, and I plan to replace it soonest.

But because I suspect the clutch to be near its end of life, and because I plan to upgrade it to Cosa 2 clutch, I may as well do it simultaneously with cruciform. So I've chosen the SIP Cosa 2 clutch series. Specifically this one:

https://www.sip-scootershop.com/en/product/clutch-sip-cosa-2-race-21-teeth-for-primary-65-67-68-teeth-for-vespa-px150-e-lusso-ab-95-98-my-cosa-2-125-150_93403200

And here's the confusion. SIP states that this 21 tooth primary fits 65, 67 and 68 tooth cush gear. I'm confused. In my simple mind, when you change the number of teeth on a gear, it's diameter must change too, in order for the tooth spacing to remain the same. If this is so, then gear meshing will be affected too, considering that we can't bring the shafts closer together. So how does this work then?

I understand that if I put a 21 tooth primary, same as factory one, I don't have to worry about it. But let's imagine I want to put a 22 instead (which allegedly fits my 68 tooth cush). Does this really work?

Thanks in advance

Yes. The tooth contact point moves further in. 22/68 is usually a good choice. If planning for more than the usual bolt on kit. A 23/68 cog is a better choice.

Thank you very much for the wisdom. Can you please give some heads up on what makes 23/68 a better choice? Is it the ratio, or tooth meshing?

I haven't stated, but I plan to put 12" or 13" wheels on my scoot, so I have to account for overall ratio stretch.

Thanks

This will change everything. Decide the gearing once you got the wheels. Might be ok as it is.
Personally, I think the 12" wheels look awful and have no real advantage but if that's your thing...

Even 11" based on my own experience.

Different strokes for different folks

I'm open to hearing about technical issues with what I have in mind (for an example, maximum rim width that fits forward is 2.5"), but as far as looks go, I'm in peace with my choice.

Wheel diameter doesn't make a lick of difference on your gear ratio decisions, only the outside diameter of the tire does. If you wanting to figure out which gearing to go with on the 12" wheels, you need to first buy both the tires and wheels that you want to use. After you get the tires mounted on the rims, then measure the outside diameter of the tires to figure out the optimal gearing.

If you're wanting to go with a wheel that's wider than a 2.5", you'll have to cut and space the engine's swingarm in order to center the tire in relation to the frame. If you also want wider than a 2.5" wheel up front, you might have to cut, twist, and reweld the fork as well.

If you have all the tools and knowledge, then that's all very straightforward. If not, then bodging would be another option.

Thanks for pitching in. 👍🏻 I made my pick for the front, it's gonna be a 13x3 rim, which fits the fork, but without a tire. 😁 Some fork work will be required. Front makes no difference to gear ratio, I'll agree.

Still need to do measurements in the back, before I commit. I've heard about offseting the engine by modifying the swingarm, but how much in order to fit 12" or 13" remains to be confirmed. Also, how it interacts with the exhaust.

This is going to be a challenge, but that's what I like about it. Hopefully I won't throw away too much moneys in the process. 🤞🏻

I'm not going to judge your aesthetic choices on a 10" vs 12" vs 13". You do you. But if you're wanting a taller tire for performance, it will do just the opposite. A bigger tire will weigh more and have a larger contact patch. This equates to a higher rolling resistance and slower acceleration, worse braking, worse fuel economy, more power being robbed climbing hills or headwinds.

If you're still hooked on the look of 13", then realize that modifying the muffler will probably be the easiest part of the project.

The engine's swingarm will need to be moved over to the right about 1/2" or so. That means you'll have to cut off that same amount of material off the swingarm. A spacer will then need to be installed back onto the other side of the swingarm.

The upper rear shock mount should also be relocated over to the right the same amount as swingarm. If you don't do that, there will be a side load on the shock's rod (piston) and eventually it will definitely cause the seals to blow on the shock. It might also cause fatigue on the very upper portion of the rod and cause it to snap off (i'm not joking). There's also close to a 100% chance that the tire will rub against the shock's coil spring if upper shock mount isn't moved over to the right as well.

Of course when the shock gets relocated over to the right, it won't fit because the frame is in the way. You'll need to notch out the frame (and weld back in) sheetmetal to give structural back to it.

Once the frame it notched and sorted, then you'll have to either have to cut out a large portion of the right side cowl and just leave it open, or weld back in a raised bump, or just run with no cowl at all. If you have E start cases then it's even more cowl notching involved.

Once you have the rear sorted out, then you'll have to cut and turn the front fork so that the tires track together on the same plane.

The easiest way to do all of this is to flip the scooter upside down on a pair of sawhorses and first find dead center of the rear tail of the frame. Once you have the rear set, then it's just simple to work your way forward to make the fork align with the rear. And when i say simple, it's because a frame jig must somehow be incorporated to align everything correctly. It would be pretty much impossible to do free hand. Just having the fork tube welded onto the fork link off 1/16" of an inch, could put the alignment at the wheel off 3/8"~1/2"!

And let's not forget about gearing. Of course you'll need a 36t short 4th gear to begin with. possibly a less teeth on the clutch as well?

I'm not trying to scare you off. I just want to give you full disclosure. I'm not really a fan of the aesthetics of super tall wheels like that, but i do appreciate custom builds such as the one you're describing.

whodatschrome great!

That's some valuable advice there, thanks. I'll admit that I haven't even considered the rear shock.

I have some experience in truing a bike on the jig, which will come handy. I'll just have to make a jig befitting of Vespa's corpulence.

Re. the front, I'll be fitting a 110/70-13 tire, which will require me to notch the fork about 10mm. I don't plan to cut it completely, so it should not veer out of alignment too far. Jig will help for sure.

On the rear, I would like to run a 140/60-13, but that a respectable 25mm wider on both sides of the wheel, relative to OEM choice. Hopefully that half an inch of swingarm mod is enough.

Did I mention that I plan to fit a GS style body kit? https://www.sip-scootershop.com/en/product/frame-kit-gs160-style-for-vespa-px80-200-e-lusso-98-my-t5-lml-lml-star_90719100

Can you run it by me again re. the 4th gear? I understood that gearing will be too long in 4th. For some reason I believed this issue is only related to PX200 gearbox. I didn't notice the big rpm drop between 3rd and 4th on my scoot.

Cheers

notched fork and a GS body kit?! I'm getting a suspicion that we're all being trolled here…

Geniuses are often misunderstood

I'm taking cues from this "beast", image curteousy of Rocket Garage blog.

Best I start a build thread, with photos.

This needs a lot of work to proper install and ofc GS handlebar.
Almost all P what I saw with that kits looks absolutely terrible.


This one is from Scooter & Service and it was HUGE work. As almost all their projects.
You MUST to cut fork and turn and rotate the lower part relative to the upper part to get right wheels alignment.

Care to elaborate as to why?

It is better to read and learn by your own. Especially with my bad english it is hard and will take too much time to explain all.

You can start here and then do your own search and research - there is more info on this lovely forum and on other internet.

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Five
Six

Oh wow! Way to consolidate all of those projects. That couldn't have been easy. I might as well add in one more link to make seven-
1958 VB1 200 wideframe Briar Blue project (Post 2731196)

Yes! It is what I'm thought about but couldn't find(as I didn't leave any comments there and didn't add the thread to my faves) - only "Wideframe scuttle bucket" jumped out.

P.S.
I follow and read about all your scooters - I am delighted with your skill and the amount of work done.

Oh wow is right. Man, you sure can weld!

My friend used to tell me "you're boiling the ocean mate", and that's your own choice clearly.

However if you're really going to all that trouble, why not start with a fork that's made for a bigger wheel and tyre anyway? LX, GTS or whatever. The idea that you're going to cut a chunk out of the fork leg gives me the heebie jeebies.

A mate did an LX conversion on his smallframe, he had to cut the very top, re-thread and re-cut a steering lock. WAY easier than trying to force the 13 into the 10 space.

Rear shock. Check out what Jurgen does on his... he was looking for additional wheelbase for a little more stability with his 400. So moved the engine back (amongst so many other things) which required the shock mount to be altered. Lots of interesting approaches on this scooter.
This is a PX frame, he's done a nice job to disguise it with the kit roland87, except for the horncast which even the funky paintwork doesn't cover unfortunately.


?si=X5EZst9guxBNN0aM

So much info is packed into that video. I don't understand a lick of german, but i'm still going to have to come back and watch that video 5 or 6 times in order to get some future fabrication ideas! That scooter build is very well thought out!

Isn't there? That guy really really knows his stuff. Thought you'd like it.
Check out some of his exhaust videos, I'm sure they'll inspire you.

To translate, click the 'CC' to show subtitles. Then click the settings gear icon, you'll see this below. Click on Subtitles, then Auto-Translate. That will bring up a list of languages to choose from.
It's slow going because there's quite a few errors but you can get a pretty reasonable idea. If you use Chrome there is also an option to have the translation read to you. Sounds like a good idea but I found in practice it was worse than reading.

I knew I was gonna like this forum, ever since I started reading CM's build thread long ago. You guys rock, thanks for all of your inputs. 👍🏻👍🏻👍🏻