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The Cyclemaster Flywheel Hub and How She is Fixed

by D Turner, C.Eng, F.I.Mech.E

Chocolates with hard centres are fine, but soft flywheels with hard centres tend to leave a nasty taste in the mouth.

About two years ago, Andrew Roddham told me that all his flywheels on his Cyclemasters were loose on their hubs and asked for ideas on how to fix them. I took one home and repaired it. It was then fitted to his machine which, among other things, did Lands End to John o'Groats in four days. The repair has held, so Andrew asked me to write down what I did to effect so wondrous a cure. The trouble is, I can hardly remember what I had for lunch today, so I certainly couldn't remember what I did to repair a flywheel two years ago. It was thought that I should take another flywheel home and fix it (this was Andrew's thought, not mine) and such an action should stir my memory of what took place.

First of all, there is no point at all in trying to join things together if there is a lot of metal dust, oil or dirt between them. It is a job requiring some patience, but the hour or so spent is a good investment. Cleanliness is important, but what you use as a cleaner is even more important. If you are going to use one of the Loctite compounds you must not use any petroleum-based cleaning agents as a solvent. Trichloroethylene is OK, so is Loctite primer and activator; methylated spirit is probably OK too, but definitely not Bostik thinners or cellulose thinners.

My method of getting the muck out is to grip a tapered punch (pointed end up) in the vice and drop the flywheel onto it so that the centre bore is jammed tightly on the punch. The outer rim of the flywheel can then be rocked, squirmed, wobbled and squelched about while the cleaning fluid is floated into the gap around the loose hub. By checking the underside occasionally and wiping off the dirty liquid, one can eventually tell that the cleaner is coming through clean. One can then also tell that there is a fair bit more clearance than when one started the job.

At this stage there is a temptation to put the Loctite Retainer or Loctite Engineering Adhesive into the gap; don't do it. Leave it for several hours, preferably in a warm place, so that all the cleaner dries out. This is important.

After a suitable time, put the Loctite around the gap and work the flywheel on its hub just as you did for the cleaning and flushing process. Keep adding Loctite and keep lifting the flywheel off the punch occasionally so that you know when it has percolated through.

When it is seen to be through, with the punch still in the vertical position, put the flywheel on it and waggle it about in all directions, and up and down, finally leaving it where you think it is central - ie: not biased to any side. You can't guarantee that it will be right but it's pretty sure to be better than it was!

The secret now is in the refitting of the flywheel to the engine. Fit it carefully, keeping your fingers crossed while so doing. This makes the operation more difficult but is all part of the magic.

All that now remains is to run it in carefully; I would strongly recommend you keep your speed below 60mph for the first 1000 miles.

First published - April 1991

Additional comments

by Andrew Pattle

The flywheel referred to in this article is the Wico-Pacy Series 90. This flywheel is also fitted to many other makes of cyclemotor: Power-Pak, Mini-Motor, Cyclaid ...   The problem can also occur on other flywheels of similar construction, ie: where the body is die-cast around a steel centre, the Wipac Bantamag for instance.
The problem seems to occur sooner with the Series 90 than with other types, and particularly on Cyclemasters. Why Series 90s are vulnerable must be a result of their particular construction. But why Cyclemasters? The problem could be exacerbated by running at high temperature; differential expansion of body and centre will help the separation process. The Cyclemaster has the flywheel in an enclosed cover nestling in the curve of the exhaust pipe, so it gets quite warm in there. If your flywheel is OK, consider running it with the cover removed; this should prolong its life.
One further point: the Series 90 has two types of steel centre: newer ones are hexagonal, earlier ones are knurled. If you are making the repair on a knurled centre flywheel, be careful not to twist the flywheel around the centre, upsetting the timing.

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