Skip to content

Contra-rotating Cranks


Back in 1939, Harold Willis’ answer to BMW (whose motorcycles were dominant in racing during that period) was an engine for the Velocette Roarer with contra-rotating cranks, because he thought that BMW’s longitudinal crankshaft setup affected handling. This engine was essentially a 498cc twin cylinder, but, only one of the cranks drove the clutch and the gearbox. The pistons in both cylinders rose and fell together, but one cylinder was used for supercharging the other, and its crank was used to cancel the gyroscopic effect generated by the other. When I read about this bike, I wondered why there are no engines with contra-rotating cranks anymore, until I stumbled upon the following engines…

Revetec engine

the Motoczysz C1’s engine

Neander’s diesel engine

I think there might be more of these kind of engines which I haven’t found yet.

What I find really disappointing with the current state of motorcycles is that most of them use the tried and tested formula – twin spar aluminum frame, inline-4, telescopic front suspension and a swingarm on the rear. Exceptions, if any, are rare… What is even more disappointing is that BMW is following this path with the S1000R, in spite of having a reputation for doing things their own way. Come on BMW, we need something different ! How about companies going their own way and coming up with innovative and competitive designs like Norton did with it’s rotary engine?



2 thoughts on “Contra-rotating Cranks Leave a comment

  1. It’s not only about handling, but first about balancing. In that, BMW did come up with their own solution in their 800 parallel twin: a 360 deg. twin with a reciprocating balancer, driven by a third throw in the crankshaft. Yamaha did the same in their T-Max scooter. It works so well they even allowed themselves to leave out the middle bearing. And, of course, no more need for expensive gears. This solution is so obvious that one wonders why nobody thought of it before. It might have saved the Britisch twins….

  2. A few years too late with the reply… BMW did come up with a solution already solved by the Yamaha XS650. Yes, the twingle was supposed to solve things and now we have 270 degree BMW. On the scooter note, we can chat for days about how tweaking stuff can improve cost efficiency. This blog is not about that…

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: