Moto Guzzi Robin Sprocket

I have a Moto Guzzi Robin that I am restoring. I had an idea, and I wanted to get your opinions on it. there are two chains on my moped, obviously. One for the pedals, and one for the drive from the tranny. The chain to the tranny is much wider than the chain for the pedals. In theory, if I could switch out that front sprocket for a more narrow one, and replace the drive gear on the rear wheel with a mountain bike "set," and use the mountain bike chain and tensioner, I will have created a multigeared transmission for a moped that was orginally a single speed. This would increase low end torque, and increase top end speed. The question is strength. Do you guys think that the change in chain width would make the chain too weak to handle the power from the engine??? Do you think the idea is way out in left field? I just wanna know what you was just something playing around in my mind, and I wanted to get some response before I give it a shot. I am very mechanically inclined, so I probably wouldn't have any problem doing the switch....

Re: Moto Guzzi Robin Sprocket

Ron Brown /


At first glance, this sounds clever. After all, how could a 500 cc moped motor load a chain more than a mountain biking gorrilla with a full head of steam?

On the other hand, you may find yourself uttering the magic words, "oh sh*t" as the chain feeds its self to the hub and locks up the back wheel. Keep in mind that you must have the free wheel mechanism on the rear sprocket and that the sprocket assembly will be considerably wider than the standard one.

But hey, go for it and post pictures.

Oh, try not to do anything to the Robin you can't reverse, I have a soft spot for Guzzies.


Re: Moto Guzzi Robin Sprocket

Reeperette /

This has been tried, and it did not work so well as that, alas.

The chain did break, more than a few times, but the main problem came from switching the little gadget to make the chain jump to the other sprockets.

Consider the speed and Rpms of a mountain biker going full-gorilla flat out VS the 6000-7800 Rpms that a moped engine will throw - not only did it saw up the chain and sprockets in short order, but more often than not it would throw the chain entirely, or jam it between the sprockets, which is a right pain in the ass.

Now the guy who did that did eventually find a semi-solution, with a little help from yours truly, as far as that kind of system...we found another, smaller sprocket of the same thickness as the one that came on the back wheel originally....and drilled a couple holes and bolted the smaller one to the outside of the larger one, using the original moped chain with a very modified ten-speed flipper-thingie (whatever the hell they call those).

So he wound up with a two speed that served fairly well, and didn't throw or lock up the chain when he shifted, I guess you'd consider that a marginal victory there.

Let us know how it goes tho, for future reference....Good Luck.


(Oh, FYI - that 'ped was a Puch single speed, if it matters any)

Re: Moto Guzzi Robin Sprocket

Well, I could do that....the only problem is that I have a couple of questions for you...First....where can I buy new sprockets?? much modification did the "ten speed flipper thing" take? I sure it took plenty, but I'm curious as to if any springs or actual mechanics of the "flipper" had to be changed??? Thanks for all the luck :)...I'm sure I'll need it....I will defininetly post before and after shots and performance comparisons on the site it all goes well...

Re: Moto Guzzi Robin Sprocket

Reeperette /

>>First....where can I buy new sprockets??<<

I suspect you can find them at many moped shops, I would try mopedjunkyard first....but we found ours digging in a cycle salvage yard, so no real idea what it came off of to begin with.

>> much modification did the "ten speed flipper thing" take?<<

A lot.

>>I'm curious as to if any springs or actual mechanics of the "flipper" had to be changed???<<

We didn't really mess with the springs, we just hand to bend it out wider, then it broke, so we had to make it bigger so the chain would pass through it without hanging, and we played with the mounting for a long time before we were satisfied with it.

We also wound up adding this little pincher-gear kind of thingie, one wheel over and one under the chain, on a spring bracket so it would move with the chain when you changed minimize the damn thing throwing the chain off, why it helped, I dunno - but it did.

Good luck, this is a really frustrating mod to try.


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