I removed the cylinder and the piston is at BDC resting against the front of the crankcase . Now the crankshaft moves anti-clockwise and the piston rises about half the distance of its stroke. Clockwise when resting backwards
The engine sprocket and timing gear are removed so the shaft can turn freely.
Does that mean it is well balanced 
John 
email (option): john.kater@chello.nl
The quick answer is no..
Conversely though, it doesn't mean the balancing is incorrect either..
It is simply the case this is not a viable method of testing crank balance..
Crank balancing is a procedure which is quite complicated and should be regarded as work for a professional unless you are prepared to spend the time studying and understanding the procedures and have the equipment to carry them out..
It would not really be possible to describe that here without a very lengthy post!..
Most standard cranks are in a reasonable state of balance. The BSA balance factor was 58% for these single cylinder engines but there was a production tolerance so they are not always absolutely accurate. Never the less they run within reasonable limits usually.
If you are particularly concerned about having the smoothest engine you can then get them rebalanced by an engine shop to a 60% balance factor...
Note also that having the flywheel assembly running true within the specified limits will have just as much, if not more, effect on smooth running...
There should be no more than .002" run out on the main shafts and .005" run out on the flywheel rim faces.
The main shaft tolerance is the important one of those mentioned...Ian
email (option): ian@wright52.plus.com
It would not really be possible to describe that here without a very lengthy post!..
It is no use anyway Ian, because I do not even understand why the piston rise from BDP, keeping in mind the weight of the piston.
John
email (option): john.kater@chello.nl
Hi John...The flywheels are round but have more weight opposite the conrod and piston (the bobweights) to counterbalance those parts when the engine is running.
So, if you turn the crank by hand and stop the crank with the piston between top dead centre and bottom dead centre, the weight of the bobweights will fall to the lowest point in the crankcases, slowly turning the crank and moving the rod and piston as it does so....Ian
email (option): ian@wright52.plus.com
Hi Ian,
I spoke to a professional from a workshop about this matter. The piston should stay motionless in any position. In my case the piston is to light because it rises (half its travel). 
John
email (option): john.kater@chello.nl
I don't agree that UNDER THE CONDITIONS YOU DESCRIBED in your initial post the crank will stop in whatever position you choose, even if it is correctly balanced...
I state again that this is not a credible way of determining whether the crank assembly is correctly balanced...but I'm not about to enter into a discussion on the subject....
If you have concluded that your crank is out of balance based on what you have told your professional and what he has told you, then I suggest you strip your engine down and take it to him for rectification...
However, assuming you have standard flywheels and an original piston you will find this a wasted effort, apart from having the opportunity to eliminate the minor production tolerances present in most flywheel/piston assemblies...
And to improve the 'balance' of your engine shops bank account.....Ian
email (option): ian@wright52.plus.com
I have "1949" flywheels and a Heplex 470 gr.piston (with rings).
John
email (option): john.kater@chello.nl
Ian, in my earlier post I thought that my Heplex 0.60" o/s piston was too light. Now, after searching this forum about this matter, I know that my piston (with rings and pin), is too heavy with 557 grams.
John
email (option): john.kater@chello.nl
I spoke to a professional from a workshop about this matter. The piston should stay motionless in any position. In my case the piston is to light because it rises (half its travel).
John
Maybe I did not understand the professionel correctly, not with the piston but a small weight of 7 ounce must be attached to the small end.
The wheels must remain stationary when places in any position for static balancing.
Not rocket science if you ask me.
John
email (option): john.kater@chello.nl
OK...Assuming 7oz is the correct weight to apply in your case..what are you going to do if it is out of spec. and doesn't stay where you put it?...
The test should also be done with the crank assembly on knife edges or on rollers...Not in the crankcases with the rod resting against the crankcase...Ian
Hello Ian,
All information is on BSA service sheet 712X. And I will ask the people from the workshop for the static balancing. I know them from earlier work on my engine.
John
email (option): john.kater@chello.nl
Making friends here, Douglas