Modifying cowlings for AF flywheel..

[J1MS]

First if your fitting a small flywheel modify the casing by removing the alloy that would normally be the edge to a standard flywheel As Paul Green has already shown... (The pick-up on the stator has white paint on it, which is in line with the laminates, this is to help align the magnets on the flywheel on assembly... incase any one noticed and wondered what was going on)


Then the head cowling needs to be give a cooling fin (Similar to the Italian GP) to help direct a little more air to the exhaust side. A cardboard template was made first, from this the fin cut from a sheet of steel, the edge folded in a vice and then clamped in place onto the head cowl.
The welding was done by drilling small holes in the cowling (but not through the cooling fin) these lined up with the fold of steel from the cooling fin, then welding the two together through these holes (plug welding), then a tack at either end with the mig to prvent it vibrating... (A spot welder would have been better)...
This fin helps cool the hottest part of the barrel a little more than on a standard SIL cowling. pic below...

In the pic above, I also add a second 8mm bolt hole to the head cowl, so that it can be bolted onto two long cylinder head nuts instead of just one as standard, giving four mounting points, which has to be better...
The last thing to do is to make sure the flywheel cowl is as tight a fit as possible to draw air in and push it into the head cowl where it cools the engine. The one in the picture has had the front face of the flywheel cowl cut off and then slid down till it touches a piece of card layed over the flywheel while all bolted to the engine and then tacked back in place then the small front piece which joins to the head cowl was cut out of a piece of sheet with snips and folded and beaten to shape then tacked, then the cowl was unbolted removed and welded with a mig, the fit is now so it sits about 1mm from the fins before it was about 20mm...pic below

The plug welds can be seen in the picture above that secure the fin into the head cowl an easy way to weld when no spot welder is available...

[J1MS]

I posted this as I thought I had seen far too many scooters with fantastic kits well set up but when a small flywheel is fitted the cooling is a little poor but this seems to slip by on the build, a well cooled engine will normally run better than a hot engine and the cooling on the original was intended for a low stressed standard motor not 20-30 HP TS1's and RB's, and I dont like seeing blown motors when I know how much they cost and hard they are to get to the finished state...
So I hope my post is of help to someone...

[byron]

yes thanks, everything that can be done should be done to keep an air cooled running cool.
like the extra cowling mounting trick too

[CANbus]

So I hope my post is of help to someone...

Yes it is and I always enjoyed reading your posts and viewing your photo’s J1MS, this one has certainly got me thinking.
I have a lightened AF flywheel and went out for a blast yesterday here in NZ, I kept getting nips that stalled the engine, the ambient temp would have been around 22°c which isn’t that hot for this time of year. Once I removed the side panels I had no problems.

There could be a number of things that caused my issues, so before I start to pull off the carb too rejet or check the timing etc I thought I’d check the basic stuff and I couldn't help but notice my flywheel fin tip cowling clearance, it measures around 20mm .

Would anyone know what the fin tip to cowling should measure as standard?

I see the cowling you use J1Ms the fins are very close, is this custom made or purchased from somewhere?

Thanks.

[minotaur]

as close as possible without touching, 1mm

[soulsurfer]

I see the cowling you use J1Ms the fins are very close, is this custom made or purchased from somewhere?

Thanks.

The last thing to do is to make sure the flywheel cowl is as tight a fit as possible to draw air in and push it into the head cowl where it cools the engine. The one in the picture has had the front face of the flywheel cowl cut off and then slid down till it touches a piece of card layed over the flywheel while all bolted to the engine and then tacked back in place then the small front piece which joins to the head cowl was cut out of a piece of sheet with snips and folded and beaten to shape then tacked, then the cowl was unbolted removed and welded with a mig, the fit is now so it sits about 1mm from the fins before it was about 20mm...

[cezeta]

as close as possible without touching, 1mm

i was thinking of filling my fan cover with expanding foam then spinning the fan so it carved out its own shape but leaving the fan tight to the cowling. if it ever touches then its only foam.

anyway i asked mbd their thoughts and they have done the same with good results. not letting the fan carve the foam though, cut it and shape it.

if anyone wants a head cowling with a fin inside then look out for spanish ones as they have them too. i picked up a few on ebay for a tenner each.

[Knowledge]

Excellent thread J1MS. Well written with good photos.

I had a long chat with Ian Frankland about this at the last Peanut Duck. His solution was to fit a doughnut of polythene plastic inside the cowling, machined to the specific depth that is required to stop the cavitation of the air (cavitation is where the air rolls off the tips of the fins, rather than being pushed along by the fin).

This seemed a pretty simply alternative solution, and it avoids the need for any welding to the fan cowling.

I have a Beedspeed plastic fan on my Ducati lightweight flywheel (boy, does it sound good when you blip the throttle, but ....) and the fins are much nearer the centre of the flywheel than on most flywheels. I am about the construct a new cowling with a smaller hole in the middle, so that the fan functions properly. I would fit a doughnut with a smaller hole, but the fins are already 1mm from the inside face of the fan cowling.

It is good that you have highlighted the matter, J1MS

[soulsurfer]

What happened to the MB "Turbo" cowlings

[GP Kevo]

I think those will debut with the new MB auto advance / retard electronic ignition.