Scooterotica

It seems to have become a Lambretta "fact" that SIL lengthened the fins on their flywheels to increase cooling but that in practice it made no difference.

Has anyone ever actually tested this?

I ask because my 240 is suffering cooling problems and I know for a fact that the fuelling and timing is spot on as it has been set up on a dyno. I have a spare Indian flywheel and cowling and wondered if it was worth fitting.

And a supplemental question for a further 10 points: Who does the best high efficiency fans?

ArmandTanzarian wrote:I know for a fact that the fuelling and timing is spot on as it has been set up on a dyno. I have a spare Indian flywheel and cowling and wondered if it was worth fitting.

And a supplemental question for a further 10 points: Who does the best high efficiency fans?

Dyno is only part of the picture and is no guarantee that it is set up sorrectly as there is no load as you would get on the road. A third gear full throttle run won't tell you what your engine is doing in all conditions and throttle positions. Did you dyno guy road test the bike too and check the plug?

There is a lot of debate regarding fans and cooling and more recently cowlings and their proximity to the flywheel fins. There is also a preference to have a fin inside the cylinder cowl to direct air flow to the exhaust side. I'm not convinced on these plastic fans either

I'd be interested to know too, the indian flywheel I have just bought for my Ally 225 engine has the long fins. I bought a long fin cowling but I'm not sure if I can use it with a std (125S) head cowl?

If you fit one of the flywheels with the longer fins you may then run in to problems accommodating it behind your foot board. So that is something you will need to look out for. Are you sure your problems aren't related to your particular barrel before you start?

and with longer fin flywheel cowling, you need to then make sure that there is no gap to cylinder cowling, or fill that appropriately...
I wanted to buy a cylinder cowling for longer fins at wicksteed to go on a bike I was working on, but nobody seemed to know of one... surely that needs to be longer too, to reach the edge of the flywheel cowling.... i ended up making up an alloy plate to fill the space, otherwise all the air was just coming straight out on the outside of the clylinder cowling...

I appreciate that a dyno run isn't everything but its as close to a definitive answer as I'm likely to get.

The operator took lots of temperature measurements while doing the dyno run and said that there was a heat build up on the side furthest from the fan that would be eased by better airflow. He also suggested a re-profiled cylinder head design but obviously that wasn't something that could be done on the spot.

Short term, I have a big finned flywheel and cowl sitting in the loft and if it helps, I'll fit it. If someone sells a better designed fan then all the better.

Lambrettas are notoriously undercooled even in standard trim, doubling the power output and raising the rpm makes it all much much worse especially during sustained high speed cruising.

If my plan for the ultimate cruiser is to be realised then I need to get this sorted.

running an af lightened flywheel in an italian cowl, i have pushed the cowling as close as possible to the face of the flywheel fins 1 - 2mm distance.

the distance from the outer diameter of the flywheel and the cowling diameter is a lot in my opinion , especially at the bottom.

just filled the flywheel with expanding foam, ready to carve out to fill the gap, as anyone any recommendation on the diameter gap difference from flywheel to foam?, do i have it at 1mm at 12 0'clock 3mm at 3 and 10mm at 6 o'clock positions for instance????.

as anyone done a test on this as i know it's been talked about recently

I was looking at my cowling yesterday as I've just fitted a long fin flywheel that I had in the loft.

The gap at the bottom struck me as being huge. I can see that the gap might need to be bigger to encourage the airflow into the cylinder head but what the optimum is I can't begin to guess. Trial and error is probably the only way to find out and even then it will be quite hard to measure subtle changes.

Good luck and be sure to let us know how you get on

Just by the by, but I bought a GP electronic kit off Scooter Restorations last year with the flywheel fins turned down. Although, we still ended up having to extend the cowling. Not sure if they weren't turned down enough or what.

If you look at a fan laid on top of a cowling the size of the gap is very apparent:



A completely unscientific guess based on no knowledge at all would suggest that the red area could be filled.