Modern Vespa

Hi all,

Over the summer I was curing issues with two bikes and swapping cylinders and pistons. I have a spare new SS180 cylinder and piston on the shelf and went to fit it to the GS160 crankshaft but the piston shaft was thicker and wouldn't go into the crank.

I assumed it would be the same as the GS160. Does this mean that I need to swap the crank to accept the piston shaft if I want to fit the cylinder and piston?

Do the GS160 and SS180 have different size piston shaft?

I'm talking about the shaft on the right hand side of this picture btw.

Thanks!

Piston pins are different. If I'm not mistaken, the only option was to use a special O.S. piston from Grand Sport and reboring your GS160 cylinder. Unfortunately the GS pistons are not available anymore…

https://www.sip-scootershop.com/en/product/piston-grand-sport-race-180-cc-big-bore-for-vespa-160-gs_75004000

The common thing to do was replace the connecting rod of the GS160 crank with one from an SS180. They accommodate a wrist pin bearing. The rods used to be available separate but I don't know if they are now. The crank assemble has to be pressed apart to swap the rod.

The SS180 wrist pin uses a needle bearing and the GS160 has no bearing just a connecting rod bushing.

There was a conversion piston made by Meteor in the sixties but they are hard to find. I have one new in the box. It is made to fit a stock GS160 rod/wrist pin but the piston is the size of an SS180.

I found the connecting rod here.

https://www.scooterwest.com/rod-kit-ss180-090648.html?srsltid=AfmBOoqs6O-eU0moZB-nfC-11o2csA7WB8ZRISsKAbmCYUW9x39M-rHs

This might be better for you.

https://www.sip-scootershop.com/en/product/conrod-kit-mazzucchelli-90684-for-vespa-160-gs-2-vsbm-0036098-180-ss_BCO0500?cr=e993ab67-6807-4109-bbed-f6374ebf9f9b

OK, thanks for the info, so the change in piston requires swapping the connector rod, but that requires the crank to be removed and disassembled.

Much thanks. I don't need to do it now luckily.

I have two different GS160 cylinders and pistons. One is much larger than the other. I assumed the bigger one was an SS180 item. Maybe it's just a custom item.

C

Is Grand Sport still in business?

My supplier told me that the owner moved to Taiwan and got married to a local. He now works for SIP supplying parts made there. Apparently SIP brought all stock. On their site though they have the following announcement…

Shame. They did good stuff.

I have not seen the GS brand pistons available for the GS160 for quite a long time.

Sadly, there are not many GS160's left in the world. It's a very small market to sell products to.

Best revving piston I've ever had.
Wish I could get another one

Are Meteor the same thing?

Unfortunately, no. They were custom made by Meteor for Grand Sport…