400cc pistons VS 500cc pistons

Hello everyone,

As presented, I'm trying to restore an 500cc Gnome & Rhone 500cc ABC motorcycle.

I bought, a constellation of boxes including pieces and I try to reassemble 400cc and 500cc engines and one bikecycle.

The external diffirences between 400cc and 500cc motors are clear.

Now I try to understand if the pistons of the 400cc and the 500cc engine are or not the same.

If they are the sames, I will be able to remake (400-500cc) pistons. In the other case I have to know the dimentions of the 500cc pistons

Does anyone have any informations to help me on this point?

Regards, Frédéric

Bonjour Frederic,
I have an Illustrated Spares Book of the Gnome et Rhone, but it is of no help in solving your problem.
Only one part number each is given for piston, piston ring, and crankshaft. There are two numbers for the cylinder, of course (left and right).
I wonder how many 500 cc. models were made: perhaps too few to warrant issue of a separate Spares Book.
Several G&R machines went to Australia, and Ozzie Harry Beanham certainly had a couple. Howard Burrows knows more of this than I. Over to you, Howard...

G'day Frederic & Paul.
Yes I own Harry Beanham's Gnome Rhone that he bought on 19 March 1923 and still owned it when he died on 1 September 1996, his ownership lasted 73 years and 9 months. He was a character that's for sure, at one time he declared he wanted to own every ABC in Australia and I think he got fairly close!
We are moving into our new home tomorrow morning so an early rise is called for (not used to that anymore) and when I am living there I will be able to tally up what I have in the way of ABC parts....I did buy my old mate Len Masser's ABC after finding a small note to Harry amongst the paperwork I also bought at his final auction detailing who owned it and giving an address.I also bought a lot of the spares that were on offer at the sale.
The second ABC on offer that day was sold to a VMCC member who later sold it to Yesterdays NL, its pictured in their Archives and its the one with the American saddle.
I did find a pattern for the ABC pistons amongst my bits and pieces (I think I only have some of what is needed) and will take some photos of it tomorrow. I seem to remember a mate having part of the puzzle.
I am afraid I cannot comment on the 500cc version...apart from the collection of parts on this site some few years ago I have never seen one in the flesh.

Greetings All,

I have been watching this thread and thought I would toss my bit in for the record. My ABC had severely beaten up pistons due to the usual valve failure in its somewhat checkered and violent history. Some years ago I replaced them with a small Daihatsu car/truck piston. Pin height was the same, dish top but the gudgeon pin was all that required attention. I think I also 'wasted' a fair bit to get the mass down to relieve any stress on the rods. Even though they are pistons designed for water cooled use I have had no issues so far. They also have an oil scraper so she doesn't smoke as much! If anyone is interested I will try and find the information which I am sure I have tucked away somewhere. They should be relatively easy to source.

The great thing was that I did not have to re-bore as they went straight in!!! Also, being ABC barrels, they were not worn at all in spite of the many dusty miles.

Happy ABCing

Guy

P.S. I am still looking for a rear brake back plate with shoes and drum if anyone has one they can spare. I would like to fit it to the front wheel to improve the stoppers a bit. This may be a 'mod' which we can all use after I sort out the bugs if there are any. Also a set of original'Rams Horn' bars would be nice if such things exist anywhere.

G