Re: Vespa + HPI Mini Rotor


Thanks for the rundown man. Much appreciated - I will put that to use.

My first attempt was pretty crude. I took an old crank and tried to make a cutter from it. I machined a cutting surface into the tapered portion and cut out most of the material behind the cutting edge. Even after my ghetto hardening attempt it dulled instantly and didn't do a damn thing

Re: Vespa + HPI Mini Rotor

Bring it over Max looks like a lot of fun. :))

Re: Vespa + HPI Mini Rotor

@ scootertrash

I had a lot of fun catching up on your builds. I dig the new stuff

got some work done this weekend. grabbed the old rotor in the lathe, trued her up and measured the taper at exactly 6 degrees


Used a small cutter to get in there and bore it out. Got the clearance I was looking for


New problem.... I was so focused on pushing the rotor into the case to get clearance from the frame, I failed to notice there isn't enough room for the stator under the rotor anymore - the mini rotor is way deeper than the stocker. I'm going to have to get really creative to get this stator mounted. probably going to have to machine back more of the case and get stupid close to the crank bearing/seal

gunna have to stew on this one a bit... major facepalm on my part

Re: Vespa + HPI Mini Rotor

Hah! Hey I have some junk to play with if it helps. Thin scooter pulley, shave off the teeth. Punch a hole thru it then weld the cheek where ever it fits.


I shimmed the crank to bolt one on a hobbit. A lot different than vespa but the thin cheek is useful.

Re: Vespa + HPI Mini Rotor

A spacer that fits inside. Thread the spacer and use it as the rotor nut. Put the thing together and bolt the ramp plate into it as well.


Make me a sammach!

Re: Vespa + HPI Mini Rotor

Notch that bad boy open.. heck u could even slip it on in reverse, ramp plate first, with that flat top rotor. I installed one in reverse on a hobbit motor using spacer shims and grabbed the crank using the clutch wedge. LMK


I cut the teeth off the cheek hunh?!?


Re: Vespa + HPI Mini Rotor

I like that. no meat grinder action on your calf

Re: Vespa + HPI Mini Rotor

A new one is cheap. Hah


Re: Vespa + HPI Mini Rotor

Randomly woke up this morning at 5am totally determined to make this shit work.

Last time I worked on this guy, I cut the taper on the rotor to bury it deeper in the case. When I did that, it looked like there was no way there would be enough room for the stator anymore. I was pretty bummed after all the effort to cut the rotor - I put all this crap in a box and set it aside - again.

I was laying in bed scheming about making custom low profile windings and testing if there was enough current for the CDI to trigger. I remember reading some good stuff someone posted years ago about light coils. When I got up, I figured this time before trying to reinvent the world I should see how much room I have to work with.

I drew the stuff up in fusion360 and was stoked to find out there was just enough room between the crank seal and the rotor for the standard HPI stator to live.


That meant the next step was to see how how the frik to get something to mount under there. I cant drill tap into the case under the stator holes without hitting the crank bearings. Once I rotated the part I could see the mounts had to sneak out between the windings.


Then I realized, duh, that's how HPI does it with their stator plates. I was able to machine more of the OG stator plate from the back side to clear the case where the crankshaft bearing bore. Then I cut the case mounts down another 3 or 4 mm and whammy, the shit fits.


Time to counter sink some screws for the stator plate to accommodate for the ultra tight plate/rotor clearance and I should be back in business.

Was glad to see that this has taken me so long that there's already a bigger, badder case and cylinder from malossi ~facepalm~

EDIT: Had to lol when i realized this has been going on for 3 years now, holy hell (edited)

Re: Vespa + HPI Mini Rotor

And room for some big ass fan and cover ??

Re: Vespa + HPI Mini Rotor

@marc yup


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Re: Vespa + HPI Mini Rotor


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Re: Vespa + HPI Mini Rotor

3D printed fan?

Looks cool man.

Re: Vespa + HPI Mini Rotor

Yup. Thanks dood

If it explodes or melts I’ll have to finally learn to run the CNC at work

Re: Vespa + HPI Mini Rotor


Re: Vespa + HPI Mini Rotor

I bought a roll of PETG for my Ender 3 and i am thinking it might be tough and flexible enough to survive fan duty... its really strong in the x/y plane but it doesn't bond layers super good so not as strong in the Z.

i have made some little airbox parts with it and its fuel/oil resistant. on my printer i run it at the very top end of the heat range to get the best layer adhesion. also warps like crazy so you need a glass bed.

if you wanna send me your model i can print ya one... its just the amazon basics brand and its pretty cheap but you'll need to do some dicking around to get the print settings perfect... print some small test pieces, haha.

Re: Vespa + HPI Mini Rotor

@Graham I knew there'd be a few fellow printer nerds on here.. I think you're right on the money about PETG. I've bee working my tune for a few weeks now.

Printing has been my obsession while taking a break from mopeds.

For PETG, I use a buildtak heated bed, too much extruder heat, and a lot of cooling fan to help with layer adhesion. Usually means running some coast and extra retraction. Running .8 nozzle with .4 layers. I've also used really soft TPU for carb/airbox booties and it works great.

Here's a pic of my modified duct on the Titan extruder. I'm a firm believer that high heat and fast cooling makes for a strong part


Re: Vespa + HPI Mini Rotor

oh shit you are way nxt lvl to my shit, haha, wasn't trying to talk down to ya... surprising how a lot of people have never heard of PETG. i like it way better than ABS plus i've had samples sitting in gasoline for like 4 months now and they are still lookin good... maybe a little more brittle but not much.

yeah i definitely have to set up a better cooling fan rig. my ender3 is basically un-modded, i see it more as a tool than a toy so i've left it alone. the glass bed was great but i'm always down to get stronger parts, i know the PETG has more in it so maybe i'll try pushing hotter

Re: Vespa + HPI Mini Rotor

Welp, I got her together. All the timing marks on the rotor were removed by machining so i had to start blind. I used a timing light and slow-mo on my phone to try to get it to fire at TDC. One I had it firing at TDC I rotated the crank to TDC and made a firing mark on the fan.

Next, I put a small amount of advance and gave it a shot. It was a dog. Waaay too little timing. I was actually pretty stoked that it would even fire and hold an idol, so I called it a success. Now to get more accurate about timing...

My hand drill is supposed to spin about 2000 RPM so I used this graph and a little math to set my timing at 23 degrees at what I was guessing was 2000 RPM (at the time, I was not considering that the drill was probably spinning lower than 200RPM due to the force it takes to spin the motor over)

That was wayyy too much timing. It got to 340 Deg on the stand pretty quickly and didn't want to stay idling.

When I pulled it apart this time to adjust the timing mark was like 30 degrees retarded. I was scratching my head until I pulled the rotor/fan and found some carnage:


I'll have to build some clearance in for this wire retainer dooder, or maybe flip it to the bottom of the stator


When the meltdown started, I'm guessing it shifted the fan's position on the rotor making my new timing marks useless. I'm now 3D printing a timing indicator that locates on the flat of the crankshaft. I'll use that to make some marks on the rotor so I'll be able to mount the new fan any which way without losing my timing marks.


This sucker is really testing my patience. I look back to the days in Rat House where we'd mock some shit up after a few beers, cut/weld/grind/hack some spare parts together through the night and ride a new build to work that next morning.

Miss those days...

Re: Vespa + HPI Mini Rotor

Lots of math this morning

TLDR = after lots of number crunching, this kit will want 2.4mm BTDC when the timing marks align (if they were still there) and I have a plan of how to set the timing


I looked up the static timing suggestion from the Malossi manual for the DEPS kit and they like 19 deg BTDC

Next step was to try to graph (as best I can from the low res HPI picture) what the curve is on the Mini Rotor. My RPM will likely top out around 10k the way I'm setting this guy up. I took an average from 0-10k rpm and it was 19.5 deg BTDC. I then shifted the HPI curve -.5 deg to approximate the best timing curve for this cylinder.

The HPI firing marks (if i still had them) align at max advance which with my adjusted curve is 24.5 deg BTDC. Using 86mm conrod length and 43mm stroke, the piston should be 2.4mm BTDC at 24.5 degrees BTDC.


So I didn't really learn anything except the "Set the firing mark at 2.5mm BTDC" is damn good advice. - no surprise there..

Now to set timing without timing marks..

I now have my power drill set in low RPM mode with a fresh high capacity battery so hopefully the increased torque will more accurately hold it's max RPM (600). I've now marked the 600 RPM firing mark on the case. Next step is to find out where the crank shaft should be at 600 RPM.

I expanded my graph to show better what's going on from 0-1000 RPM. It looks like 600 RPM is dead on 17.5 deg BTDC


After some lunch, I'm gunna hold the rotor at it's 600 RPM firing mark and rotate the crank until it's at 17.5 degrees BTDC. That should get me timed exactly on the money. I'll then make a baseline timing mark on the rotor with the tool I made yesterday. I'll just make some index marks from there +/- and I think I'll be able to make adjustments without even removing the motor from the frame.

Sorry if this shiz is drawn out and boring, but it helps with my thought process to type it all out

Re: Vespa + HPI Mini Rotor

it worked

Here's a look at my rig to mark crank location on the case. The ruler is clamped to the flat on the crank so it stays consistent


I set the crank at 17.5 deg BTDC and used the mark I made showing the 600 RPM firing location to mark the crank location on the mini rotor - this way the fan marks don't matter if something shifts. This turned out to be a good idea - later on, the fan started shifting once the motor fired up

Once I had a mark on the rotor, I used my new timing tool to locate the crank in relation to the rotor. Then I used a 02 sensor socket to bang the rotor onto the taper of the crank so it would stay until I could nail it down with an impact


I think the next step is going to be making a more secure version of this fan. The screeching sound at the end of the video is the sound of the fan dancing around on the rotor. It's shifting around all over the place. I'll either have to epoxy it together or make a new more secure version. Either way, the current fan design is super efficient - I was revving it a bunch on the stand and I don't think I got over 200 deg F


Re: Vespa + HPI Mini Rotor

ᴛᴇʀʀʏ ᴅᴇᴀɴ /

I had to make an aluminum plate and rivet the plastic tfr fan to it to make it work on my ciao's ktm 50 ignition, I'd go with a mechanical connection like that

Re: Vespa + HPI Mini Rotor

Thanks for the last few posts, I was trying to figure out where to set the timing on my ktm 50 rotor. I initially wasn’t getting a strong enough spark to fire my timing light so I picked up a cdi box from a motorized bicycle engine. It seems to have a curve when spinning the crank with the drill. I set it at the 17.5 btdc and got it to fire but the idle set too low and it stalled. When I tried to restart the pullstart cord broke. It was good to hear the engine finally run.


Re: Vespa + HPI Mini Rotor

hey joe

i tried one of those motorized bicycle ignitions on my ktm mini rotor and it has a timing curve that actually advances around 8k. it ran really good at first but would break up, i fucked with the fuel system and changed out carb parts for like a week before i threw the light on there and figured out what was going on. spinning it with a drill wont get it fast enough to show you

Re: Vespa + HPI Mini Rotor

> Graham Motzing Wrote:

> -------------------------------------------------------

> hey joe


> i tried one of those motorized bicycle ignitions on my ktm mini rotor

> and it has a timing curve that actually advances around 8k. it ran

> really good at first but would break up, i fucked with the fuel system

> and changed out carb parts for like a week before i threw the light on

> there and figured out what was going on. spinning it with a drill wont

> get it fast enough to show you

Good to know. Do you know if there is a better ktm cdi box I didn’t want to buy another dud. The motorized bicycle cdi was 7$ I figured it was worth the gamble. I also wonder if all the bicycle cdis are created equal. I’ll have to check it in the higher rpms with the timing light when it’s running. (edited)

Re: Vespa + HPI Mini Rotor

The 32 bucker eBay cdi has never let me down

Re: Vespa + HPI Mini Rotor

> Daniel '' Wrote:

> -------------------------------------------------------

> The 32 bucker eBay cdi has never let me down

I grabbed this one, I had spark with this ignition but it was very weak. It wasn’t enough to trigger my timing light. I wasn’t sure what was causing the issue so I picked up the motorized bicycle cdi and the timing light worked.

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