Balancing of a Commando Crankshaft

I am in the engine overhaul stage of restoration of my Norton. I will soon be ready to have the Commando crankshaft that I am using balanced. I need reference to somebody that does this work.

Where in the world are you.

I was thinking of doing this during my current rebuild, but had problems finding someone reasonably local to do this. several car shops who advertise balancing, but I was not very impressed when I called them (what's a 360 degree crank? from one of them..)
Anyway, talking to one of the very few older brit bike experienced workshops here in Copenhagen, I was mentioning this. He reckoned that since the Norton crank is rather short, and on the Commando it's all rubber mounted anyway, there was not a lot to gain.

/Steve in Denmark.

I had a crank dynamically balanced on one of my Commandos, it was well worth the effort and made a big difference to the smoothness. My problem is that I live in Hong Kong and would have to send the crank to the US, UK or Australia to get this done, otherwise I would do so every build, You have to send the carnk complete with con rods, pistons etc so that they can weigh everything.

Or, you can weigh the components yourself and just send the crank and the weights of the components. Really not too difficult to do.

Really no way getting around shipping that big lump of a crank though.

The only times I would re-balance my crank, is if I fitted heavier rods or pistons. The balance factor determines at what revs the motor will run smoothly. Dynamic balancing can improve secondary balance (the rocking couple across the length of the crank) however is not usually necessary unless you are using a mix of crank parts - old and new ? - I'd never do that.

Well worth the effort. Mine was balanced some time ago and, other people remark that it is the smoothest commando they have ever ridden. And I run a 4 thou clearance.
Unfortunately Triton motorcycles of melbourne had the work done for me and he doesn't to nortons anymore. He did mention that the guy who did it had a "special" way to balance the crank and it was expensive. $80 ! Obviously I said just do it.

johno

Could those people who report an improvement after Dynamic balancing their cranks please post if it was a 750 or 850 ?
There is a theory that Ive heard that says the 850 cranks were better balanced.

I doubt that the Norton factory individually balanced the crank in every Commando engine. They might not even have changed the balance factor to compensate for the heavier pistons when moving from 750 to 850cc capacity. My 850 crank did not have any balancing holes drilled in it as standard, apart from the big hole in the other side of the fly-wheel, to which I fitted a threaded and punched and loctited steel plug to make the motor suitable for rigid mounting. With the plug fitted, the balance factor came up to 72 %, which is very good for my purposes. I started to look for more, but stopped before I started drilling holes which might weaken the flywheel. My motor is super-smooth at 6000 RPM, but rocks when idling. You would not do that if you intend to use the motor in a commuter bike with isolastics .

SteveBorland said:

Could those people who report an improvement after Dynamic balancing their cranks please post if it was a 750 or 850 ?
There is a theory that Ive heard that says the 850 cranks were better balanced.

Click to expand...

I had my MKIII crankshaft balanced static & dynamic and it made a huge difference.
My machinist said he didn't think the factory made much effort in balancing the crank to start with.
I use a local (Cincinnati O) machine shop that specializes in racing engines for cars and boats. They will work on motorcycle parts if you ask nicely.
Ride On
Dave