Scooterotica

I've heard it said on another forum by that Knowledge chap that a gap of 1mm is desirable between the fin and the cowl for optimum cooling. I have a SIL flywheel that's been turned down and should be the correct height. However it will scrape the inside of a standard flywheel cowl. A very clever friend of mine has modified a cowl so that it is deeper with the result that I now have something more than 1mm clearance. I'm a bit concerned by this and don't think it's an ideal solution. Will it really reduce the cooling. If so what should I do, whip the flywheel off and get it turned down another couple of mm perhaps?

Very few people go to the trouble of getting the clearance down to 1mm, including myself, so don't worry. I am sure it will be fine.

My response to Corrado's enquiry was the best I could come up with to his very specific needs. If you are building a fan to blow air over the cylinder for his application, then it might as well be as efficient as possible (well, why not?), but it does not mean that if yours is less efficient, it will cause a problem with over heating.

Doom Patrol wrote:I've heard it said on another forum by that Knowledge chap that a gap of 1mm is desirable between the fin and the cowl for optimum cooling. I have a SIL flywheel that's been turned down and should be the correct height. However it will scrape the inside of a standard flywheel cowl. A very clever friend of mine has modified a cowl so that it is deeper with the result that I now have something more than 1mm clearance. I'm a bit concerned by this and don't think it's an ideal solution. Will it really reduce the cooling. If so what should I do, whip the flywheel off and get it turned down another couple of mm perhaps?

Don't get it turned down any more, providing it is only scraping slightly (i.e. it still turns over ok) them try lovering the cowl out from the fins and if that doesn't work you can file the holes that the mounting crews fit though. That should give you enough clearance to stop the scraping, check where it is c=scrapping first as you might not have to releive all of the holes.

I've had all kinds of trouble with this. On my GP I resprayed the flywheel cowl and it was looking great, then I forgot to Loctite one of the screws which fell out on the motorway. The cowl then skewed and started scraping on the fins. Terrible noise and it burnt all my lovely paint off in a neat crescent.

I seem to remember it was Taffspeed that recommend the 1mm clearance and I think it really helps to suck the air in. I have a Mugello engine in a Li S3 with just about a 1mm gap and when wearing shorts you can feel a blast of warm air on your right leg.

Ben

and when wearing shorts you can feel a blast of warm air on your right leg.

On a Lambretta scooter. How very dare you??

Thank you all for the replies. Given Martin's advice it may not be anything to worry about. Although, if I do relieve a standard cowl I will have the score marks to guide me at least.

just to balansce the argument,
i have an indian rayspeed s type with af lightened fly wheel under an indian long fin cowl.
the gaps are massive but no over heating issues.