Monday, July 26, 2010


A curious racing motorcycle appeared in my mailbox today, of an engine configuration I've never seen.  I have an idea that the chassis is a Smith frame from Australia, which was a scaled-down Norton Featherbed built to house mainly Velocette engines for 250cc racing, and which was based on the Beasley frame from England.  That this machine uses Velocette forks, gearbox, and wheels supports the theory.  Typically, Velo MOV pushrod engines were used in such frames, often with special cylinder heads in bronze or aluminum cast by enterprising tuners such as Carey.  Some frames housed sleeved-down KTT engines, which were certainly heavy but fast and durable.
Australian racers did battle far away from the epicenter of the motorcycle industry; spares took months to arrive, and tuning advice dispensed in a mere trickle from the factories.  So, the 'bush tuners' made their own racing heads, frames, or whole engines.  It appears this curious motor is entirely home-made, and appears to be an 'OP' (opposed piston) engine, in which two oppposed crankshafts move two pistons towards each other in a common cylinder barrel, forming between them the combustion chamber at the top of their stroke.  Fairly common in marine applications and sometimes aircraft, such an engine is very rare on a motorcycle!
There are as many variants on the internal combustion engine through its nearly two-century existence, as there are dinosaurs with outlandish teeth, armor, and body shape.  And, most are equally extinct, for the moment.
Can any readers shed light on this machine's history?


The Velobanjogent said...

I've raced a Smith framed Velo special in the past and the frame looks like that made by Nugge Smith, but the steeper front down tubes seem to be the question recollection and looking at pics the tubes sloped back more on a Smith frame.
Nugge never numbered his frames, made a little over 20...BUT..Dennis Fry in the past borrowed Nugge's frame jig, made his own off it and himself made a small number of frames, possible 6.
They fell out over this.
Dennis comes to the Sydney Velo club nights. I'll try to remember to take a copy of this photo and quiz him....
Kindest regards,
Dennis Q.

Nortley said...

It looks like an OP engine. Note the chain which frames the side of the engine, and its sprockets, big equal sized ones top and bottom, and idler/tensioners front and back. Given the relative size of the idlers compared to the crank sprockets, and that the engine is air cooled, I doubt they drove any accessories, but using one as a blower drive could be interesting. But, by the carburetor and exhaust locations, it looks like it is basically two two stroke singles joined at the head joints, giving essentially two engines sharing a combustion chamber. OP diesels, which were quite successful, had the scavenge (transfer port equivalent)ports at one end of the cylinder and the exhaust ports at the other. At least, that's what this appears to be...

Anonymous said...


Thanks for posting such an unusual engine. I've never seen
a opposed twin with common combustion chamber before. Two
crankshafts....Wow! I can't help
wondering how it sounded and ran.


Anonymous said...

Hey Paul,

Is that a marine engine? I remember something but don't have any documentation.

Larry D.

John Nienhuis said...

Hi Paul,

I am 100% sure that a picture of this bike once appeared in a copy of Classic Racer, end of the eighties - start of the nineties.
With the picture was a little bit of info. So 'we' have to find that copy of Classic Racer - I will try to dig out my collection somewhere this week.
Cheers, John Nienhuis from Holland
aka Sidecarracing

occhiolungo said...

there is a decent animation of an OPOC motor here:

The motor in your photo could be similar to half of what is shown, with opposing cranks though.


DAN_DAN said...

Sorry i'm no help on this one, but great post
I finally got where the exhaust pipes and carbs were sprouting from. Def should get an award for not using pushrods this early in the game of race bikes.
Got to love those aussies!

John Nienhuis said...

Found it!
Spring 1990 issue of Classic Racer.
The weird and wonderful 'Barker
headless' twin crank four piston racer of 1957...that's all I'm afraid!
Cheers, John

John Nienhuis said...

It seems to be described in here:

Cheers, John

Anonymous said...

Why is he wearing mary janes?

Vegavoxbanjo said...

Back from the Sydney Velo group club night...Dennis Fry was there.
He didn't make it and there are several, like me, who had Smith frames and the consensus is that it isn't a Smith frame and so unlikely to be in Australia.
Kindest regards,