Vespa + HPI Mini Rotor

Been a little while since i've been on here. I'm putting together a Malossi Ciao motor and I thought i would document what it takes to put a HPI Mini Rotor on a Ciao.

Anyone who's done this wanna chime in?

First hurdle was machining the posts flat. I'm starting with the Malossi Points case for my build. I was told that was the one that worked best with the HPI.

Here's one set of HPI's instructions: This one indicates to machine the posts to the same height as the center ring. The instructions that come in the same box as the ignition say to machine the posts 2mm below the center ring. Considering two of my posts were lower than the center ring to begin with, I decided just to make them flat (cut the tall ones to the size of the short ones)

That's all fine and dandy, but once you level out the posts, the provision for the crank seal (red arrow) hits the stator before the stator sits flat against the posts (white arrows). I used a die grinder to open the center of the stator to clear.

Next, the stator is cut for a 3 bolt pattern, but the case has a 4 bolt pattern. NBD - i made a template and drilled a 4 bolt pattern on the stator. I'll set the timing with the key-less rotor.

Stator Mounted with low profile screws to help clear the rotor:

now that i have the stator on, the rotor sits way too far away from the stator coils. I think the stator would still work, but it would work better if i bury the coils all the way under the rotor. To fix this, i ran some washers under the stator to shim it out.

alright, now we're cookin, right? well kinda. if i install the pulley and clutch (single speed) there aren't enough threads to get the nut on. So i measured across the motor from the right case half to the rotor, and sure enough, the motor is wider than the ciao frame is

Looks to me like i need to move the ignition closer to the case. that means i'll need to re-cut the taper on the rotor deeper to pull that in as well.

I'm gunna make this work, but I'm a little surprised there's this much work involved... It was easier to put a Honda ignition on a V1 than it was to get this together..

I've been debating how to cut the rotor accurately. I'm leaning towards making a cutter from a used crank


Re: Vespa + HPI Mini Rotor

ah crap. looks like i should have had a plate that bolts to the case that the stator would then bolt to. that would have converted me from the 4 to the 3 bolt pattern. woops

Re: Vespa + HPI Mini Rotor

So if I'm reading this right., if you alllign the stator plate to the lowest of the four posts that would hold the stock coils, than the taper of the crank doesn't allow for the rotor to be low enough to cover the coils. So it sounds that unless you remill the taper you should first press and bolt the rotor to the crank and that could actually be done before the crank is

Put into the case. Based on the where the rotor fits is where the stator needs to be set.


Far so insane. What r u doing for a fan? My conception is that this calls for water cooling of

At least the head. This is why Vespas are insane to mod past a mild build u less you are a genius with a complete machine shop that u know how to use at your disposal.

The guy who figures out a good solution taking a

Case and fitting


Hpi reliably and with a

Fan has got my order. Otherwise after

Months of



Mcivering I am back to 6 v plus points.

Re: Vespa + HPI Mini Rotor

I looked on the HPI website and based on the instructions yeah, it looks like there's supposed to be a plate that goes on first. Maybe you can contact them to get it? (edited)

Re: Vespa + HPI Mini Rotor


I will try bolting and tightening down the rotor to make sure I'm not being a dummy. But otherwise you're on to it. With the stator bolted down on the posts and the rotor installed, the rotor sits 3-4 mm higher than I would like. You can see the coils starting to peak out under the rotor. I bet if I had that mounting plate that I'm missing under the stator, it would have pushed the stator out perfectly. But that still wouldn't solve my problem of getting the motor into the frame. The motor is about 1/4" wider than my ciao frame is and I don't even have a fan on it yet

I'm on the fence about the fan. I'm leaning 80% towards a mechanical stock type fan setup and 20% towards an electric fan above the cylinder. The mini rotor should make plenty of juice if I go electric. I wonder how long an electric fan on a rigid 2 stroke would last though with all the vibration

I am no genius, but I do have free reign over the machine shop at work. That's like 80% of why I started working there


I might do that. It would be pretty rad to adjust the timing with the stator without even removing the rotor

I think I'll take it into work today and make a plan

Re: Vespa + HPI Mini Rotor


holy shit, look at that nut in your case. (edited)

Re: Vespa + HPI Mini Rotor

Like Marc said, The guy who figures out a good solution has got my order as well.

Re: Vespa + HPI Mini Rotor

Team Vespa Derek Wrote:


> holy shit, look at that nut in your case.

didn't realize. Malossi wants you to run the bolts from the case out and i liked it better running them backwards. I belt the bolt head fits the case nicer

Re: Vespa + HPI Mini Rotor

Looks like HPI did not do its homework before marketing this product. Even getting the stator and such on right, we found in a mock-up that there was no way you can install the front variator -- as the variator uses a spacer to sit on top of the stock flywheel -- and that problem must be dealt with as well. I doubt HPI ever had this working on a real motor, and assumed that if it delivered a rotor with the appropriately-cut taper, it would work.

Re: Vespa + HPI Mini Rotor

I got an internal rotor hpi on my race bike. When I get back in town I'll take some pics and post some info. I didn't machine the mounts, and I ended up not using the adapter plate either.the taper problem was my only real issue.

Re: Vespa + HPI Mini Rotor

Nice, please post Tyler! I did a writeup on my HPI mockup to send to the manufacturer. I saw no possible way of getting the variator on without machining down the hex on the rotor. Even then it was not looking real good, there was no room left to have a fan on top of the rotor.

I was going to make the fan too, but gave up after the above issue.

Re: Vespa + HPI Mini Rotor

I'm gonna decide to risk it and run no fan. Even doing the Terry dean style fan, ain't gonna happen with the hpi spacing. Mines on a race bike so I'm hoping short run time should keep me out of the red zone.

Re: Vespa + HPI Mini Rotor

Please take some pictures Tyler, I've always been interested in a Vespa HPI system.

Re: Vespa + HPI Mini Rotor

made a little progress. i machined the center of the stator to clear the crank seal when i plunge the stator deeper into the case. then machined the rim off

the taper only really sits on about 3/4 of the rotor, so i took about 1/4" off of the bottom of the rotor's center section. i painted the crank to transfer to the rotor to make sure i wasn't cutting anything that was touching the crank

i think i'm going to make a small boring tool from 3/16 HSS to cut the taper. maybe this weekend

Re: Vespa + HPI Mini Rotor

i wish i had progress to report, but instead here's a closer look at the problem

Here you can see the fan/flywheel sitting well below the case:

here you can see the the mini-rotor is sitting well above the same reference point

Re: Vespa + HPI Mini Rotor

attached is my drawing of the issue last time i looked at this.

Bottom spacer plate is not required.


Re: Vespa + HPI Mini Rotor

Maybe just expand the frame a tad?

Re: Vespa + HPI Mini Rotor


Push that shit out a tiny bit

Re: Vespa + HPI Mini Rotor

Maybe a bit late

But if you weld 2 tiny iron plates (like on the picture

You might be aible to mount a plastic fan

Re: Vespa + HPI Mini Rotor

It's not too late, that was a very similar idea to my backup plan actually, i just never bothered to make the fan since getting the HPI to work in the first place was such a disaster.

Re: Vespa + HPI Mini Rotor

hpi is one of the easiest to adjust

if you know what your doing

in my case ive got a polini evo kick engine so its cdi ignition

the coil mounting points are a bit more sunk in then the points version

im thinking about making a simple sunk base plate

so if i mill the rotor it will sink an additional 3.8-4mm

what would be perfect for the thread clearance

Re: Vespa + HPI Mini Rotor

hpi is located in belgium

only an hour drive will check if they can offer baseplates and offer out off the box install/plug and play

with and engine in front off their noses it should be easier

Re: Vespa + HPI Mini Rotor

i use to have the same problem with the thread

im using a si subframe

the polini vario tends to run into the subframe

so i used a singlespeed clutch spacer and some of these

but modified to this

Re: Vespa + HPI Mini Rotor

Any progress?

Re: Vespa + HPI Mini Rotor

Grande Guru Wrote:


> Any progress?

Re: Vespa + HPI Mini Rotor

Finally some progress. I opened up the frame to fit the Mini Rotor so it can be installed after the engine is fitted to the bike. This allowed me to run without a fan. It rips super hard after being able to adjust the timing. Unfortunately the aggressive timing and high compression are too much without a fan and it gets super hot.

I still need to cut the taper on the rotor to push it deeper on the crank. I'd like to be able to install the motor into the frame with the rotor already installed.

In the mean time, I drew up and 3D printed a fan to work with the stock fan shroud.

Going to try a simple PLA press fit fan for now. If my prints dont stand up to the heat and RPMs, I'll try cutting one out of aluminum. You can probably spot my base spacer in there too. Looking to bump around 2-3mm to drop compression and get the exhaust timing around 185 degrees.


Re: Vespa + HPI Mini Rotor

This is above my pay grade but...the way to make a Vespa tame the heat probably is the mlm water cooler Vespa head. The perfect solution would be a one way bearing on the rear clutch as in the one way bearing on the front variator of a Hobbit. Then fit whatever cdi u want and forget the fan. That one way bearing requires invention. The Vespa heat is even worse than Hobbit heat.

What kit is on that mallosi points case ? Isn't it cut for a 46 mm kit. Which of course has near zero clearance from one or more studs. What did u use and is your ride hot because of that ?

Re: Vespa + HPI Mini Rotor

Hey Marc. I’m running the 47mm DEPS kit. It ran pretty good on points, but there was a lot left on the table. I have mad respect for anyone running a water cooled setup, but that’s just not what I want for this bike. I want it to look more subtle than some of the other stuff I’ve built. I probably would have stuck to points except I love how HPI stuff build revs so damn fast.

Try number 3 fit pretty well. I wonder if it’ll explode at 8k rpm...


Re: Vespa + HPI Mini Rotor

Dirty30 Dillon /

Nice work on this, a viable option outside the malossi CDI would be great for vespa.

To reply to Marc: Vespa's really aren't that wild in terms of heat. The small head obviously doesn't shed like others, but having wrap around fan cooling mean that the cylinder is actually cooler than the head is typically.

Re: Vespa + HPI Mini Rotor

i dunno if you figured out the taper cutting thing or not yet but this is how my toolmaker buddy taught me to do it

#1- put the crankshaft in the lathe in a 4-jaw so you can true that fucker up to the .0001 in terms of runout, put a dial indicator in the actual tool holder of the lathe, like, clamp it in where you would put the cutter, measure the runout at the taper itself, because even the best crank ever won't be that perfecto. when i do them, i will use a sacrificial crank and just bash it into place with a hammer. never done a vespa but with puch and tomos i clamp to the opposite side bearing race.

#2- now you loosen up the cross slide and get the angle close. snug it down a lil' bit and run the dial indicator across the taper. at this point i use a tiny hammer or usually the wrnch from the tool holder to just tap it back and forth while running the cross slide in and out across the taper. obviously you're going to go back and forth and you want the indicator to stay at '0' +/- .0002 or so. Then you rotate the crank like 90 degrees a couple times and repeat. Usually the tapers have some surface roughness so you'll never get it perfect but you get a good feel pretty quick for getting that cross slide dialed in on the the fuckin nuts. once the crossslide is tracking the taper perfect, tighten it down, check again, and remove the crank

#3- put the rotor in the 4-jaw, true that fucker up on the inner surface- this way you keep the factory balance. Take the dial indicator out and put a boring bar in the tool holder. cut the taper to whatever size you need. I usually figure what the smallest diameter will be and use a pin-gauge to guess and check but if you have a DRO or some fancy shit you can probably just get it right on that way. the actual bore diameter is probably only +/- .005 because you can shim your variator out to whatever you want by putting a shim between the flywheel and vari.

this is how i've done it for putting different-taper stators on different cranks.

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