model 20 us export pistons

model20nut · Post by **model20nut** » Fri Aug 03, 2007 4:17 pm

I've just bought a 1955 U.S export model 20 engine. I can see why the fella wanted to sell it because it was minus the pistons and they are proving hard to find. The cylinders are bored out to a 545cc capacity (69mm). Can anyone point the way to a pair?

Don Madden · Post by **Don Madden** » Fri Aug 03, 2007 7:57 pm

If you look at the engine stamping see if it is: 55/20B. The G9B/20B were the factory 545cc varient made especially for Cooper Motors, the West Coast distributor. All twins shipped to our West Coast in 1954 & 1955 appear to be the "B" varient.

I am often asked for a source of pistons & have asked the few specialists on these motors but know of none, although they do turn up occasionally.

I suggest you bite the bullet & have some made up. JP Pistons will likely make them for you & if you buy a minimum quantitiy of assorted sizes, probably get a reasonable quote.

Post a inquiry on this forum & the Yahoo! also as there are more over here. Also send a quiry to the North American Section Secretary, (John Deiderich, cycletoys@aol.com), & ask for it to be placed in our newsletter.

Cheers, Don.

GSAX1 · Post by **GSAX1** » Fri Aug 03, 2007 9:01 pm

I saw two new ones at a jumble some month ago. Didn't buy them because I didn't think they were worth anything.

model20nut · Post by **model20nut** » Mon Aug 06, 2007 12:11 am

model20nut · Post by **model20nut** » Mon Aug 06, 2007 12:14 am

Thanks Don. I can design a piston myself on autocad and get a firm here to make one, do you know where i can get all the dimendions from? John

Don Madden · Post by **Don Madden** » Mon Aug 06, 2007 3:02 am

Sorry, I have none, & don't know of any outside an engine although the bikes are not rare here.

Try asking in the Yahoo! forum & if no results, try the North American newsletter.

As Michael says, they do turn up now & then.

According to the spares list, which you will find in the archives, the heads are the same as the 500cc. You should be able to use a piston from the G9 as a reference & the standard bore for the G9B is 69mm.

The tricky part would be the dimentions of the inside structure. Perhaps you can cut a scrap G9 piston in half for access.

If you come up with a solution, please advertize the fact so that others can share.

Cheers, Don.