Thinking out loud - - 350 RBH engine

[adrie.degraaff]

You also need a 500 clutch, 23 tooth sprocket, cam, followers, clutchdome, petrol tank and a lot more so maybe it's easier to buy a complete machine or just stay with 350.

Maybe you can enlarge it to 360cc, a friend of mine has 2 pistons wich could do it.

[nevhunter]

The crankcase, mainshafts and rocker parts are common. The longer splined mainshaft in the BAP box is recommended if the engine is an "improved" 500. There's also extra clutch plates advised as mentioned. Generally the best way to do these projects is to have lots of abandoned Ariel projects and make up what you want from the pile and sell off the residue, afterwards. Nev

[Leejm]

Why do you want to change it to a 500cc? Is it just for abit more go? If this is the the reason then you could just keep it a 350cc and add a HS cam and a high compression piston. I have both of theses in my NH, and there is plenty of go in it. It's the quickest 350 I have ever had.! And pulls very well. Lee

[adrie.degraaff]

If this is the the reason then you could just keep it a 350cc and add a HS cam and a high compression piston. I have both of theses in my NH, and there is plenty of go in it. It's the quickest 350 I have ever had.! And pulls very well. Lee

All depending on the weight of the rider.

[Leejm]

I'm 12 and a half stone, your right ardie it's about power to weight.

[paul.jameson]

Let's turn this round and look on the bright side. The crankcases, timing case and cover, timing gear and rocker boxes are all common with the 500. Your camshaft is probably an F cam (stamped on the end) which is low performance but used in the VG 500 and interchangeable with a higher performance cam. So you need a 500 crank, cylinder, piston, head, pushrods and pushrod tubes. Yes, the 350 crank will work at 500cc with a 1932-34 cylinder and piston but these are scarcer than rocking horse manure. 500cc bits are less common than 350cc bits because a) the factory made far more 350s (postwar) and b) the conversion to 500cc is so easy.

[nevhunter]

Over boring a 350 is not good practice if you go rather big as there's not a lot of metal in the wall thickness. Sleeving is a similar problem if the sleeve is too thick. The sleeve doesn't carry the load in tension. The "standard" 350 sleeve is ok but people didn't race 350's on sleeved cylinders. If you run a350 crank I would go for the steel one. You still have to use a 500 OHV conrod and remove 1/2 the stroke difference from the base of the 500 cylinder and the piston ends up at the right place at TDC. The displacement of the motor is then stroke of 350/stroke of the 500 x 498. in ccs. Nev

[adrie.degraaff]

You still have to use a 500 OHV conrod and remove 1/2 the stroke difference from the base of the 500 cylinder and the piston ends up at the right place at TDC.

Nev you have forgotten the shorter conrod making a total of 13mm taking of the barrel foot, there are standard 500 barrels with an inch foot who'm can handle that, i have done it on a 1934 OH with a Goldstar piston that was a great succes.
http://www.yesterdays.nl/ariel-1934-red ... -1697.html

[nevhunter]

Yes there's plenty of "meat" in the later 500 barrels at the flange. The VH conrod is a very nice item. I picked up a new one recently, and consider myself fortunate to have done so. The longer rod makes piston slap less noticeable. Nev

[adrie.degraaff]

Didn't have to balance the 1934 OH crank with the goldstar piston, if i used a VH conrod and maybe the bigend it would be much heavier.