Another newbie question gents. Having done a bit of dismantling I found my crank cush spring was broken, luckily it had dropped inside itself and was still functioning. Among the bits that came with the bike was a spare cush spring, etc. The sprocket on the bike was a 4 lobe, 19teeth on a square section spring, the spare cush is a 16T, two lobe on a round section spring. What bit I've found on the forum says these springs have different strengths and so I'm guessing are not interchangeable? Am I better off getting a two lobe 19 or 20 T sprocket to go with the round spring - or forget that and get a replacement square section spring? I'm guessing the 2 lobe (later) items are supposedly an improvement, hence the change. Or just fit the round section spring instead of the square? Your views? Rog.

Are we talking m20 here Roger ?
I would use original parts, 4 lobe, 19 teeth and a square spring.
Should be easy to find.

The springs are not interchangeable....

The 4 lobe parts are more common and as Mick says sticking with that set up is probably the best thing...

As well as the changes to the spring and the cam lobes when the 2 lobe assembly was introduced, the width of the splines was also changed...

So, to change to 2 lobe you need the whole assembly and it is the sleeve that fits over the crank that is the hardest part to find for a 2 lobe set up...

Also worth noting is that the two lobe sleeve looks similar to the one for the A10 but isn't the same..an easy mistake if you're not familiar with the various parts...

You can probably get an original spring from Russell Motors...or there are still quite a few used ones about...

Try a posting on the 'wanted' section of the forum...If you are looking at used springs you should be looking at an overall length of 1 5/8" or just under.
The outside diameter is 2 7/32"...Ian

email (option): ian@wright52.plus.com

Yes Mick M20. Thanks for the input. I do have a 2 lobe sleeve - everything seemed to be there for the alternative, other than it being what must be a sidecar sprocket. i.e. the sleeve is the right splines. But I will start a search for a new spring, Point taken about sizes. Thanks again, much appreciated. Rog.