Yes - the Square Four was produced in England in the late 50s-early 60s (dates approximate). It was a premium touring bike built by Aeriel which had been building smaller motorcycles for decades. They aren’t common - but you still see them around vintage bike shows here and there.
I worked with a guy who rode one and it really was a very cool bike. The 1000 cc engine was basically 2 x 500 cc Aeriel cylinder barrels, cranks, rods and piston sets with a new crankcase and 1-piece OHV cylinder head. The valves were operated by the stock <I think> 500 cc cams which were driven off the cranks in the usual Brit-bike fashion. It used a single carb under the seat behind the cylinder head which fed the air-fuel mixture into the middle of the “square”. The ignition system used points and a neat little 4 terminal distributor for the spark. The exhausts were at the sides of the engine and were also very neatly done.
The Square Four ran extremely well and was as smooth and quiet as a Gold Wing. Starting was kick-only and had a four speed gearbox with chain final drive. My colleague used to start it with his
hand - simply grabbed the kicker and pushed down hard - and away she went.
This is just a pipe-dream of mine, but I’d use a reversed XS650 head for the front cylinders (to make it easier to adjust the timing chains) and just keep the stock cams and valve gear. I’d use a modern EFI system to keep the fuelling simpler and install a Pamco system on each cam for ignition. Ideally, the “
XS1300 Square-Yam” would use a shaft drive and it would need a MUCH more robust gearbox than the stock XS650 unit for reliability. I suspect it would be easier to use an XS-11 lower end as the basis of the new power unit. Theoretically, it would be a very smooth engine with perfect primary and very good secondary forces - just like the old Aeriel.
The other way to do this would be to simply mate two XS650s end-to-end to form a big transverse four cylinder (just like an XS11, CB750, Kawasaki 900 etc.). That would be simpler, but it wouldn’t be as smooth as the Square Four configuration.
BTW - this sort of thing
IS quite feasible - check out the amazingly creative work of British bike builder
Alan Milyard who has taken Kawasaki triple two-strokes and built several four, five, six and seven-cylinder engines out of them. The recent winner of the
Practical Sportsbikes Bike of the Year Build contest is a beautiful 3 cylinder variant of the Yamaha RD350LC. The details on this RD550LC are really such that it looks like it is a factory job.
The key difference is that all of those modern-day multi-cylinder bikes are in-line two-strokes which in many respects are much simpler because they don’t need cams or valves etc
and they use just one crankshaft whereas a “square” engine would need two cranks geared together.
Anyhow, lots of fun to dream.....
The key thing is to NEVER ask ....
why....
Pete
