Thinking out loud - - 350 RBH engine

[davewasere]

Hi I have a 350cc RBH engine on the bench to rebuild. I was wondering if I could rebuild as a 500cc.
The bike in question was given to me in exchange for work I did. Pulled from a hedge in a very very sorry state.
1. To rebuild with a 500 head and barrel would the flywheel and con rod from the 350 work ?
2. Is it possible to bore the 350 cylinder out to 500 and use different stoke maybe ?.
Any advice please

[dave.owen]

You will need
Head ,Barrel,Piston,crankshaft,3 plate clutch,pushrods.

350 will not bore out to required size

have you any pictures

Dave

[adrie.degraaff]

1. To rebuild with a 500 head and barrel would the flywheel and con rod from the 350 work ?

Yes but only with a 1932-1934 shortstroke head and barrel.

[davewasere]

1. To rebuild with a 500 head and barrel would the flywheel and con rod from the 350 work ?

Yes but only with a 1932-1934 shortstroke head and barrel.

This is the first time I have used a forum so be kind thanks
Thanks Adrie. this sounds very interesting.

[davewasere]

You will need
Head ,Barrel,Piston,crankshaft,3 plate clutch,pushrods.

350 will not bore out to required size

have you any pictures

Dave

I am new to using forum's so there should be a pic attached hopefully
Thanks Dave ...so when you say crankshaft you mean the lot ? I had hoped it may have been possible to connect the new 500 top to my 350 crank at the crank pin to use my bottom end (flywheels/etc)

[adrie.degraaff]

1. To rebuild with a 500 head and barrel would the flywheel and con rod from the 350 work ?

You could also use any Ariel 500 head and barrel if you put a 500 sidevave piston in, these are easy obtainable becouse there are many around and not much Ariels for it.

[nevhunter]

The thick flange 500 barrels could have about 3/8 off the bottom without significantly weakening them. The 350 cylinders are not very thick in the wall and the head bolts are not far out. so don't overbore much. Some 350 sleeved barrels are weakened by reducing the metal too much and fail.
If you change the flywheels and shorten the rod compare the original throw of the crank plus rod length to the ones you propose. Take account of the comp height of each piston as well. Some "trials motors have a short stroke option when built with the cylinders available in alloy. Without checking fully I suspect that your piston will not reach the top of the cylinder with the 350 rod. If you obtained any 500 ohv conrod and machined a bit off the cylinder base, you could get the piston level with the top of the cylinder and still have 350 CRANK , but I would want to run the steel one. You have to shorten pushrod tubes and push rods as well . Calculate the capacity of your new engine. It will be 498 x 350 stroke divided by 500 stroke.ie Reduced proportional to the stroke change. Changing the 500 conrod from VH to VG needs a modified hardened steel bush in the bigend as the pins are a different diameter, where the rollers run. Lot of trouble. A VH 500 rod with original B/E sleeve only fits the parallel VH pin. Why not find the correct parts, and stay as a 500? Happy to clarify any of this and have the relevant parts to measure, if you can't get the information otherwise. Nev

[davewasere]

AT last attached pic...

You will need
Head ,Barrel,Piston,crankshaft,3 plate clutch,pushrods.

350 will not bore out to required size

have you any pictures

Dave

[davewasere]

The thick flange 500 barrels could have about 3/8 off the bottom without significantly weakening them. The 350 cylinders are not very thick in the wall and the head bolts are not far out. so don't overbore much. Some 350 sleeved barrels are weakened by reducing the metal too much and fail.
If you change the flywheels and shorten the rod compare the original throw of the crank plus rod length to the ones you propose. Take account of the comp height of each piston as well. Some "trials motors have a short stroke option when built with the cylinders available in alloy. Without checking fully I suspect that your piston will not reach the top of the cylinder with the 350 rod. If you obtained any 500 ohv conrod and machined a bit off the cylinder base, you could get the piston level with the top of the cylinder and still have 350 CRANK , but I would want to run the steel one. You have to shorten pushrod tubes and push rods as well . Calculate the capacity of your new engine. It will be 498 x 350 stroke divided by 500 stroke.ie Reduced proportional to the stroke change. Changing the 500 conrod from VH to VG needs a modified hardened steel bush in the bigend as the pins are a different diameter, where the rollers run. Lot of trouble. A VH 500 rod with original B/E sleeve only fits the parallel VH pin. Why not find the correct parts, and stay as a 500? Happy to clarify any of this and have the relevant parts to measure, if you can't get the information otherwise. Nev

Well...a creative solution that's not out of the question as I see were your coming from. I could do quite a bit of this but would have to pull a few favors and work out cost....but Thanks.. a lot to think about.....maybe I should try to obtain a 500 engine and rebuild this as a 350 !!!

[adrie.degraaff]

maybe I should try to obtain a 500 engine

That's not easy, you can find a loose head, barrel or crank but rarely a complete engine. .