Powerdynamo, problems in 4 strokes with weight reduced flywheels

Powerdynamo brings new ignition & light
to your vintage motorcycle



Technical Help



Problems in 4 strokes using weight reduced flywheels (in BMW e.g)

We write in our instructions e.g. for BMW systems "not for BMW with lightened flywheel" such as e.g. aluminium flywheels. Also, we clearly state that our systems are exclusively destined to replace stock ignition systems in classic and vintage motorcycles whose engine characteristics have not been modified aftermarket.

We write this as we know from experience that this problem exists and we had some quite frustrated customers who blamed us for their aftermarket modifications.
We get from time to time customers who think that there must be a solution and who bombard us with questions how to overcome the issue.
Would there be a solution, we would tell, but there is none. So, the only thing we can do, is to expressly warn. We are sorry if customers knowingly ignore this warning as they are convinced they know better.

The problem concerns ignition systems and not our only dynamo systems.

In our eyes, whatever significant modification on engines a customer may undertake (with the aim to get more power from the engine) is not a good idea and is bound to bringt negative effects. Would such changes be good, the manufacturer with all his experience, skill and money surely beyond what the a single customer has now at his disposal, would have implemented them from start. (BMW did use lighter, aluminium, flywheels for a short time in their singles and stopped this experiment shortly after as problems amassed.

In our system the advance unit sets ignition by first reading crank revolutions (in systems with external sensor by taking the time the rotor trigger sign needs to pass the sensor) and than setting the calculated time for the  spark.

Right after the value for crank revs is found the advance unit consults an inbuild table to find what the value for pre-ignition has to be. This is however not a value by angle, but time.

And there exactly is the problem with lightened masses.

If crank speed changes very rapidly the calculated time for ignition does not correspond any more to the real position of the piston. Ignition happens at wrong time with various strange effects.
This problem can not be circumvented with the material we use.

The same basic problem manifests on singles with high compression. Here kickstarting is hard and leads to quickly changing crank speed. See our info on this.
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