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Folks, I thought I'd share what I consider to be some excellent, cheap improvements to the cooling system.

I take very little credit for this, it came up during discussions with Fast and Furious (a very helpful chap, thanks) and watching some fella in Spain on Youtube called steelweasel. I've taken a little from each of their advice and come up with something I'm nearly very happy with.

First thing I looked at is probably only relevant to those of us with cheap remade cylinder heads, but important nevertheless. You can see the casting blocks the air way through the cooling fins. This was easily remedied with a file.
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This next one comes from steelweasel and although I see his point, I'm not convinced it makes a huge amount of difference, but i did it anyway, just because I liked the idea of it and it was easy/free. I domed the dust cover to promote efficient airflow into the fan. From my little knowledge of fluid dynamics, I know it will help, I'm just sceptical as to how much.


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Here, I've removed the middle of the fan cowl as it's nothing more than an obstruction. Actually I bought this already cut for a tenner and saved my original cowl.
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These next few ideas are from Fast and Furious and I think are the most important.

This plate is actually fixed in place inside the cylinder cowl but I've shown it here to explain the principle. Instead of the air disappearing out by the exhaust and doing nothing of any good, it's kept in the cowl and blown over the top of the cylinder where it really matters. Remember that the transfers cool the sides of the barrel up to about exhaust port height.
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I cut a slot to allow the air to flow freely over the cylinder head (normally, it's just blocked off in this important area). The stainless plate keeps air flowing up the starboard side of the head and upper barrel. I've noticed since i put it back in the bike that the area below exhaust level on the side shown in this photo has no air flow but is under the cowl; this portion will be cut away later and exposed to the open air.
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Some foam tape helps seal the cowl to the mag housing.
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Here you can see how effectively the air is stopped from disappearing out past the exhaust stub

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And this photo shows the section which will be cut away later as all it does is hold hot air in.
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As an aside, this is a cast 175 bored from a 150 and tuned by my own fair hand. It seized after 40 miles, which i never 100% knew the reason for, but it's sensitive to cooling (as are all lambrettas). I'm so pleased with this, that I'll be doing to future builds too.

Thanks very much, particularly to F&F.

Very interesting and relatively easy to do, thanks for sharing Dickie

The changes to the cylinder cowling as depicted were mentioned some time ago, though this is the first opportunity that I have had to see them. Thank you for showing them

In addition, any encouragement to get air to the fan & then keep it from cavitating must surely help, particularly in the instances where the smaller 'J' derived fan is concerned. Only yesterday, I measured the gap between the fan & the cowling on such an equipped engine & it was around 6 mm. In that instance, there is a flanged, alloy ring fitted inside the fan cowling that matches the 'bore' of the smaller fan to take up the space, with a spigot protruding toward starboard. Back when Group Four's were all fan cooled, I cut a semicircle shape in the LH floorboard in line with the fan & riveted a thin alloy plate to the 'board to scoop air through the cut-out. On one occasion, the plastic fan (from an auto, not electric motor) disintegrated toward the end of a race, but the engine somehow survived, very hot & smelly.

These things evolve, so I will be attempting another version of the fan cowling modification & if it works I will post some images up.

As for the head cowling, that, too, has to be 'improvable' though the precise science of the ultimate set up-may take some testing to prove. I remember Webbo removing the deflector plate in a GP head cowling on a Group Three & blaming that for the consequent seizure in the next race

Mark, yes, as I was typing this up, I was thinking I'd seen something like this before from knowledge?

I don't have a gp cowl to hand, so I'm not sure how the plate works in them.

I bought a few items from Steve Richards aka Streetweasle and the results where a drop of 20* on my CHT gauge. Also there was no change in temp from my EGT even when powering up hills

ULC Soulagent wrote:I bought a few items from Steve Richards aka Streetweasle and the results where a drop of 20* on my CHT gauge. Also there was no change in temp from my EGT even when powering up hills
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Impressive and quantified rather than just 'better'. I nearly bought these, but I'm too tight. I don't think he uses an internal reflector plate, does he?

dickie wrote:

ULC Soulagent wrote:I bought a few items from Steve Richards aka Streetweasle and the results where a drop of 20* on my CHT gauge. Also there was no change in temp from my EGT even when powering up hills
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Impressive and quantified rather than just 'better'. I nearly bought these, but I'm too tight. I don't think he uses an internal reflector plate, does he?

No Dickie, I can’t use the flywheel cover as the Bgm flywheel don’t have any space for the clip but I think with a dremmel I could make some and try and create more or better airflow into the cowling

I remember years back Allstyles used to sell a 'half' head cowling like the one above.
The theory being that hot air escaped so it was a constant flow of cooler air. They had run engines for years like that.

ULC Soulagent wrote:No Dickie, I can’t use the flywheel cover as the Bgm flywheel don’t have any space for the clip but I think with a dremmel I could make some and try and create more or better airflow into the cowling

I meant the deflector plate inside the cylinder cowling that I added. You mean the flywheel dust cover, don't you?

interesting stuff, always thought there was room for improvement with the head cowl/flywheel cover- it never seemed a very efficient set up for cooling

dickie wrote:

ULC Soulagent wrote:No Dickie, I can’t use the flywheel cover as the Bgm flywheel don’t have any space for the clip but I think with a dremmel I could make some and try and create more or better airflow into the cowling

I meant the deflector plate inside the cylinder cowling that I added. You mean the flywheel dust cover, don't you?

Head cowling has no deflector in it.
And I’ll be taking the dremmel to the Bgm flywheel and cut slots so that the dustcover retaining wire can be fitted

ULC Soulagent wrote:I bought a few items from Steve Richards aka Streetweasle and the results where a drop of 20* on my CHT gauge. Also there was no change in temp from my EGT even when powering up hills

Is this what Casa have now done with there new cooling fan?
I like this idea.
Cheers Shane.

Just mulling over this idea, radiated heat from the body of an expansion pipe can't help in this area? Would a heat shield or wrapping the pipe body help?

Solid Air wrote:

Just mulling over this idea, radiated heat from the body of an expansion pipe can't help in this area? Would a heat shield or wrapping the pipe body help?

Theoretically, wrapping an exhaust, thus retaining the heat, can influence power delivery, but it may be that in doing so may affect whereabouts in the rev range the power spread occurs. Similarly, cooling via water injection has an effect.

That said, a good expansion chamber with the correct bleed (the tailpipe diameter) shouldn't get hot like a generic exhaust will. Such an exhaust increases torque by creating back pressure, which increases torque. Not necessarily the best thing to do with a powerful kit, but some are determined to have them. I'm not sure how a well kitted Lambretta can be ridden fast on right-handers with such poor ground clearance......

Solid Air wrote:

Just mulling over this idea, radiated heat from the body of an expansion pipe can't help in this area? Would a heat shield or wrapping the pipe body help?

A heat shield would definitely help, just some polished stainless, but you'd need to keep it clean to maintain its effectiveness. I guess the section I'm aiming to cut away could be raised away from the cylinder instead of being removed and made from polished stainless. Radiant heat isn't a very effective method of heat transfer compared to conduction though so you're not gaining as much as with cowling mods, assuming they're useful cowling mods. These things work well in static situations. I've fitted them to electrical cabinets at work where we use them on ships' decks operating in hot regions. They can drop the internal temperature by about 30 or 40 degrees, it's pretty amazing how effective they are. Very different scenario though.

Here ye go fella's
https://scooterlab.uk/stickys-kit-book- ... tion-news/

dscscotty wrote:Here ye go fella's
https://scooterlab.uk/stickys-kit-book- ... tion-news/

Amazing how quickly people copy isn't it? I only posted yesterday

Good video. I hadn't considered the running board.

i'll try n post up some cowlings that I've modified over the years, also deflector plates in head cowlings that can be quite advantageous in directing flow over cylinder,

Looks like we're going over well-trodden ground. I started to think it rang a bell.

Some very good discussions here.

http://www.ilambretta.co.uk/forum/viewtopic.php?f=7&t=7386&hilit=cowling&start=20