Ohhhhh minarelli c2 belt shit?


Recently got another safari c2, had a broken rear clutch shaft when I got it. Shout out to Parker from Upjet for selling me a shaft from a parts engine of his. Anyway, she’s got a good rebuild on her, mort matched polini, mamba pipe, 4g weights blah blah blah, fastest bike off the line I’ve ever had, super happy with it BUT it’s stretching and tearing through belts in a matter of miles. And these mamma jammas ain’t cheap. I have my stock pirelli belt, I had a treats belt from a while back (the double sided cogged one), but it officially stopped starting the bike at all, and I have two new DOS belts I just got, here’s a photo of the two dos belts, one is new one has a whole 25 miles on it and struggles to start the bike, it just slips on the front vario like crazy. I can sometimes get it to start with the cardboard shit but it’s a huge hassle, and sometimes fruitless. Seems no one else has had this issue?


I DID mill the inner diameter of the rear clutch on a lathe from 14mm to 19.88mm, with a depth of 17mm to press in a one way bearing and delete my starter clutch shoes. But I’ve seen many people do this mod to Honda and derbi bikes and never heard of this issue. I can’t image that’s causing it, but who knows maybe someone will see something I did not? Any ideas? I measured the new weights they are the same OD as stock (okay it’s like .14mm smaller but pfff) so it’s not like the front is opening more than normal. I will say this c2 DID NOT come with a decomp head like one of my last ones did. But from what I’ve seen most delete it anyway. What y’all think? Any opinions or suggestions?

I REALLY don’t want to just pull start it or something, that’s the whole reason I installed the one way bearing and I feel like that’s ignoring the actual problem at hand.

Bonus photo of polini porting


Re: Ohhhhh minarelli c2 belt shit?

Run the polini with one ring

Re: Ohhhhh minarelli c2 belt shit?

Brandon Weiss (Detective brandon to you) /

Maybe it's slipping too much to begin with because there isn't sufficient tension, or the grunt of the polini is too much and just slips the belt off the line? That would chew through them pretty quick.

It's possible that texturing the pulley surfaces could help the belt stop slipping and eating itself.

Maybe you could increase belt tension a bit by getting creative with the pulleys/variator.

On top of making it easier to start, running one ring would tame it a little and maybe it wouldn't be so hard on the belts.

Re: Ohhhhh minarelli c2 belt shit?

by the picture it looks way too loose. figuring it should be pretty snug otherwise slipp n burn.

Re: Ohhhhh minarelli c2 belt shit?

> pat splat Wrote:

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

> by the picture it looks way too loose. figuring it should be pretty snug

> otherwise slipp n burn.

When I put them on brand new they are super snug and the bike will start quarter kick no problem, that’s what I’m trying to figure out. I did see the dos belts are a-20 belts and not ax-20 and from what I understand the ax belts are a bit tougher? It maybe all these after market boys are just a little too big? Maybe once they settle in from new the get too loose.

Re: Ohhhhh minarelli c2 belt shit?

Dirty30 Dillon /

If you're stretching/wearing them out it's possible your front var is pulling against an early-closing rear sheave and stretch/wearing the belts

Re: Ohhhhh minarelli c2 belt shit?

look for a wider belt, let me know whatcha find, ill be messing with one next year.

Re: Ohhhhh minarelli c2 belt shit?

I don't know a thing about these transmissions except that they're clever. But I would suggest that one good source for weird belts of all sorts is your local farm store, for farm equipment uses an amazing assortment of belts of all widths and farmers don't appreciate high prices. Our local one is called Tractor Supply Company, and Rural King is another. They also seem to be a good source for fasteners, metric and otherwise (they're selling Mahindra tractors, from India, here in rural Ohio) and there are crazy springs and clutch materials as well.

Mark Kinsler

Re: Ohhhhh minarelli c2 belt shit?

Is it possible when you milled the cheeks you didn't keep the angle and contact area with the belt correct? It looks to me the belt is wearing most at the outermost edge. The bottom of the belt looks not worn at all. Check your belt contact area and compare original cheek angle to your modified ones.

Re: Ohhhhh minarelli c2 belt shit?

> Is it possible when you milled the cheeks you didn't keep the angle and

> contact area with the belt

When you de restrict the c2 vario, it’s not actually the cheeks you modify, it’s a spacer piece connected to the outside cheek. You can see here, what I circled in red is shiny, because I faced it off in a lathe. It was longer.


Here you can see my belt is still not going the whole way up, this is because I need to window the variator next so I can allow the weights to actually push it further in. Because the weights work as almost a lever between the ramp plate and the vario this is the max they will push in stock form, I’m almost wondering if because it’s kitted and it’s not opening all the way that’s what’s stretching it? I don’t know anyone who has windowed a c2 vario yet, never seen photos anyway not even in the fb variated minarelli group. So I’m not sold on that idea. See my next post about some belt stuff I found.

Below here you can see in the middle a little bit of that “attached spacer” when it’s the original length, it does not allow them to close near this far, I took off a little more than an 1/8 inch to get this, and you can see it still has about a mm till it’s fully closed. So I never touched the ramp itself


Re: Ohhhhh minarelli c2 belt shit?

So I flipped my belts “inside out” and I noticed the inner taper is way off on these dos belts. The ribbed belt is the stock pirelli belt. It’s from the 80s and I’m pretty sure the bike had like 1000 plus miles on it from the ODO when I got it if I remember correctly. I’ll double check tomorrow but even age could cause shrinkage I was getting anywhere from 8.5-9 mm I’d bet new they were 9.2mm.

The new DOS belt (smooth) is significantly thinner. Both belts outer “wider” edge is 13mm so the taper is way off and it’s deff not gripping the way it should. I’ll contact dos about it and see if I can get some of their nos pirelli belts if I send these back.


Re: Ohhhhh minarelli c2 belt shit?

It was eating at me, so belt math, shout out to Pythagoras. Let me know if I did anything wrong, but I’m stuck here as I don’t remember how to find angles of right triangles. As you can see this is “slice” of the belt. I re-measured everything with my crappy calipers the best I could and rounded to what I think the belt was “meant” to be by my best guess. This will give me this well let me know how far off the geometry is or if it’s actually close to stock (dimensions are different but angles could be the same)

Hope my shit ain’t too confusing, anyone wanna solve that last angle for me? This is stock


And this is the dos belt


And actually just from looking, the dos belt is wider on the outside AND thinner inside so the angle will be much steeper meaning less belt grab. Hmmmmmm still curious if the actual angles. But lemme know if y’all think my logic is sound and these dos belts are the source of my issues.

Re: Ohhhhh minarelli c2 belt shit?

For the unknown angles I get inverse tangent (7.5/1.75)=76.9 degrees for the top one and inv tan(8.25/3)=70.0 degrees.

The other point I recall about V belts is that when they're bent around a smallish radius their sloped sides bulge out. This enables them to grip the flanges of the pulley more effectively than a simple wedging action would. Now, I don't know if wear on a V-belt will affect this extra grabbing ability, and the changing effective radius of your variable pulley will add complications as well.

Personal note: I have learned a great deal about power transmission in highly-stressed machinery. I attributed some odd behavior in mopeds and motorized bicycles to changes in technology and material. However, my short but observant spouse suggested that I factor in a significant increase in gravitational force upon my no-longer-so-youthful body. "I'm surprised it got up that hill at all," said she.

Mark Kinsler

she is an amazing cook, so it's not entirely my fault.

Re: Ohhhhh minarelli c2 belt shit?

I’m no mathematician so I can’t say for sure, but 9 degrees sounds like a pretty good amount of change. My issue is when I go to start the bike, it slips on the front pulley cheeks. So if the angles don’t match up it’s probably not grabbing as hard or as much of the cheek as it could be.

Re: Ohhhhh minarelli c2 belt shit?

I think it's a significant change in angle. These variable-V-pulley transmissions are used in hundreds of applications, perhaps the most common of which are washing machines, which during the spin cycle must accelerate a load of wet laundry from zero to fast with a smallish motor every few days for years. They're also used in tiny diesel cars that you cannot buy in the US, but which have been popular in Europe and I want one.

Clearly further research is needed, and perhaps a website that features discussions and tutorials on industrial power transmission would be a good place to start. I haven't tried it, but maybe the Google search terms "Industrial V-belt wear" might help.

Mark Kinsler

Re: Ohhhhh minarelli c2 belt shit?

OK, I understand the mod now. I think you're on the right track focusing on the belt angle. If the contact area of the belt is uneven it will prematurely wear out that part of the belt, cause more slip and slack.

Re: Ohhhhh minarelli c2 belt shit?

So I put a little oil on the stock belt and it brought the old letters to life I could seriously not read any of this before hand (well, barely any of it)

“pirelli” logo. Followed by “secto flex” then the belt was actually stamped “minarelli”


Now here’s the fun part, the numbers that I don’t know how to decipher,


Looks to be 7254/0 (Or “D”)

Followed by 1702049 6B

Re: Ohhhhh minarelli c2 belt shit?

Someone should be able to cross reference that. In theory...

Re: Ohhhhh minarelli c2 belt shit?

Even still I’m not 100% sure it’s all my issue is. I feel like extra pressure is getting out somewhere it should not be, it I figure even if my front is not maxing out. That should not cause “extra stress” on the belt. Because if the front is not maxed out there’s no way the rear is maxed and “pulling” on the front. It does not make any sense

Blake from dos got back to me, he’s super rad and is ganna let me try one of their pirelli belts out even though that one even does not match mine. These are uncommon engines but I love them and I want to get to the bottom of it, I’m trying to relate it to my one way bearing mod but I can see at all how it would stretch the belt (edited)

Re: Ohhhhh minarelli c2 belt shit?

Someone here has been there, done that and knows what belts work.

Re: Ohhhhh minarelli c2 belt shit?

Alrighty folks, more news.

So, I learned tonight, there are two kinds of rear vario for a c2!!!

Well one part is different, the plastic bit! And this MIGHT be a part of my issue.


Here below you can see the two styles. Mine was the top, with these super cool sharp ass rivets. The bottom is a spare I had. Ignore the red for now.


Okay, so if you read this whole thread, you’d know I milled the spacer on the front vario to allow the front cheeks to close more, granting more belt travel. That’s cool, except what happens to the rear then? It must also give more and spread open wider to take up slack. The belt itself going lower than the ware line on that photo above and it’s possible the bottom of my belt is getting chewed up on those rivets. This is a theory and I can’t prove it as there’s not enough miles on it to show a new belt line on the rear cheeks. **** see a little side note about this as well at the end

So to help alleviate this I’m going to switch the the black plastic jawn. The cheeks themselves are different, so I’ll switch the whole inside cheek over. But also, since the black plastic piece just sits in the cheek, I’d assume you could actually grind those rivets flat and have no issues. What’s left of the rivets should act like posts to hold it in place the same way the black plastic piece does with the three black oval shaped nubs.

A little something else I’m going to try, this relates to the red circles in the last photo.


In the second photo what I circled is the same piece I have circled in the third. It’s a spacer to not allow them to close any more, I’m going to try and grind that down on the lathe just a hair to get rid of half that gap or even make them touch. This will make the rear belt ride higher at idle and apply more force to the front vario. Maybe not letting it slip?

To be honest I talked to Parker about his polini and Gila c2 builds. Both run the decompression valve head and he’s selling me one. I feel like this will actually alleviate the problem more than anything. Belt can’t slip if the compression is 0 haha ¯\_(ツ)_/¯

**** regarding to the stars earlier this is a little bit of a tangent. I also talked to Parker about windowing the front vario to get full use of the front cheeks, he has and he still can’t get the belt all the way to the top of the front. I feel this might actually be part of the back vario restriction, the plastic piece in question on this whole thread acts as a stopper, the front might actually max out because the rear can’t go any further. I’ll continue this post below so I can upload another photo to explain.

Re: Ohhhhh minarelli c2 belt shit?

Scottie Hartpence /

i know this is not the right place to post this

but i just got a C2 general

I will be working on it in the summer

i am a Jersey guy and build some V1's and E50"s

working on aZa50 non oil inj. now

i would like to rebuild the C2 but not sure what tools i need

it is still stock with about 3000 miles on the speedo

i think i may be more the rear tire was pretty bald compared to the front

what tools do i need if any ,i have basic pullers,and holders,and circlip tools

never worked with a variation engine

treats just made a C2 crank and as a v2 engine /seized for sale 2/12/2021

i want to rebuild it and kit it with a polini,but don't want to break it

any manuals on what to do?



Re: Ohhhhh minarelli c2 belt shit?

Hepatitis J [OFMC] /

> Scottie Hartpence Wrote:

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

> i want to rebuild it and kit it with a polini,but don't want to break it

> any manuals on what to do?

I couldn't find a manual but only did a quick search.

Theres a diagram in the wiki

I rebuilt a v2 without any special tools, you should be fine with the tools and pullers you've got. As always, don't lose anything and take pictures as you go.

Re: Ohhhhh minarelli c2 belt shit?

Scottie Hartpence /

i thank you for the diagram

but the V2 looks like a V1 with a belt

i am not sure how to split the case

i have the V1 case splitter

not sure

it is cold here now

i will try in the spring months

Scottie :)


Re: Ohhhhh minarelli c2 belt shit?

Totally normal JBOT /

Try this.

Shim the movable vari cheek so it’s tighter at rest.

This is a common problem on hobbits.

You shim the vari to push it in farther taking up slack so the belt is tight af in the cheeks and you can pedal start.

I doubt it’s the belt angle. Belt angle in my experience isn’t that important, like almost at all.

The test for this is if you can spin the vari by hand at all when the rear pulley is locked. If you can spin the vari you have to shim it or get a wider belt.

On hobbits the shims go between the vari and ramp plate to push the vari in further at rest. The shims float on the boss.

Hope this helps. (edited)

Re: Ohhhhh minarelli c2 belt shit?

Scottie Hartpence /

built my new wheels


new rims aluminum 32 front

36 rear 3 cross each one

puch spokes

smooth hubs ripped old rims off

like a highschool girl at a kegger

detail at the valve hole purple /pink spoke


more pics to come


Re: Ohhhhh minarelli c2 belt shit?

Scottie Hartpence /

Also custom seat (I got a Guy)

got a NOS rack

Got some metal blinkers

got some rear holders for the blinkers(treatland)

new kickstand

NOS fuel tank (Treatland)

Nos Fuel caps (719 and 459) Score Treats

More pictures to come

in the spring



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