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Cooling Lambrettas
Posted: Tue Sep 01, 2009 9:29 am
by J1MS
Have just helped a mate with a 205 Honda kit which now seems to be up and running. After a few teething problems. It's making most of the power it should after a problem that caused a near total loss of the piston an bore (don't you just hate shot blast in petrol tanks). Anyway that's all sorted but the engine retains a little too much heat. When the light AF flywheel was fitted I said the gap on the cowling needs to be less so that the fan can suck more air in. Also a large head cowl is fitted which leaves a half inch gap between the cowlings. This sort of makes the cowlings as a cooling system totally redundant. It's now an insulatian with a pretty good tog rating. To overcome pinking the timing is usually retarded this puts some of the power into the exhaust as heat to stop pinking. To make power and good torque this power needs to be kept and to do this the cylinder and head needto be kept cool then the heat that's developed instead of being wasted it can add to the pull of an engine while still having reliability. That means It dosnt want to slow up if it gets hot or start pinking. So if you have a cowling that's similar to this and an engine that's quick till it gets hot start modifying cowlings so that they can do what there supposed to....:and that's cool the engine. !!!
Re: Cooling Lambrettas
Posted: Tue Sep 01, 2009 9:40 am
by whonatic
J1MS wrote:Have just helped a mate with a 205 Honda kit which now seems to be up and running. After a few teething problems. It's making most of the power it should after a problem that caused a near total loss of the piston an bore (don't you just hate shot blast in petrol tanks). Anyway that's all sorted but the engine retains a little too much heat. When the light AF flywheel was fitted I said the gap on the cowling needs to be less so that the fan can suck more air in. Also a large head cowl is fitted which leaves a half inch gap between the cowlings. This sort of makes the cowlings as a cooling system totally redundant. It's now an insulatian with a pretty good tog rating. To overcome pinking the timing is usually retarded this puts some of the power into the exhaust as heat to stop pinking. To make power and good torque this power needs to be kept and to do this the cylinder and head needto be kept cool then the heat that's developed instead of being wasted it can add to the pull of an engine while still having reliability. That means It dosnt want to slow up if it gets hot or start pinking. So if you have a cowling that's similar to this and an engine that's quick till it gets hot start modifying cowlings so that they can do what there supposed to....:and that's cool the engine. !!!
Re: Cooling Lambrettas
Posted: Tue Sep 01, 2009 8:21 pm
by mickdale
the wide cowlings tend to have gaps in the fit up with the mag flange and head cowling - is it worth sealing these with mastic?
is there a new flywheel coming onto the market made by bgm?
(or was that just a rumour)
cheers
mick
Re: Cooling Lambrettas
Posted: Tue Sep 01, 2009 8:39 pm
by davidblythe
cut the flywheel cowling down tonight to fit snugly with an AF ducati flywheel, you can actually feel air blowing through the head cowling now
Re: Cooling Lambrettas
Posted: Tue Sep 01, 2009 8:42 pm
by J1MS
mickdale wrote:the wide cowlings tend to have gaps in the fit up with the mag flange and head cowling - is it worth sealing these with mastic?
is there a new flywheel coming onto the market made by bgm?
(or was that just a rumour)
cheers
mick
Its worth sealing gaps from the Flywheel cowl to the head cowl as any wasted cooling air makes for a hotter engine... This isnt a problem bimbling around town running to the local scooter club and short rides....
But hot summer days and National rallies when your riding up and down Motorways and Long A roads, just seems to find any weakness in a Lambretta.... How many people have a scooter, then pay thousands for an engine, but worry more about how shiny it is, before they even think about how hot it gets... Then ride it locally to run it in then heat seize on the first long ride...
Mine, or one of them. I put the engine together to go to Holland 2001 I think...
Might have been 2002... Anyway the cowling was about 20mm to high missing the fan, It was the night before we set off for the ferry & no real air was moving across the inside of the head cowl. As it was a new kit not run in and needed to stay cool... So I hacked it and welded a temporary fix to get me there... It looks a proper dogs dinner... but it worked, I didn't paint it just cut it and welded and modified the head cowl so it fitted... But cus it worked its still on today 8 years later, still unpainted and rusty but the engine stays a little cooler...
Re: Cooling Lambrettas
Posted: Tue Sep 01, 2009 8:49 pm
by sean brady scooters
also butcher the N/S floor board........cut away the inner guard that prevents any cool air entering the flywheel..............
Re: Cooling Lambrettas
Posted: Wed Sep 02, 2009 12:55 pm
by lammer205
I,m very interested in this topic as i am running a honda 205 which i think runs really hot, no siezure problems though, i'm also running with a old AF lightened flywheel,i have two questions here really, when you modify the flywheel cowling to make it fit closer to the fan is there not a larger gap now between the flywheel cowling and head cowling, and can this gap be closed?Also the center peice of a flywheel cowling, the rings if you know what i mean, are these needed as i've seen quite a few scooters with this part removed is there a gain to be made from this larger opening more air getting in?One last thing if anyone has a picture of the modified cowlings could they post it if possible just so i'd have a better idea before i go butchering cowlings, cheers Hicksy.
Re: Cooling Lambrettas
Posted: Wed Sep 02, 2009 2:22 pm
by J1MS
lammer205 wrote:I,m very interested in this topic as i am running a honda 205 which i think runs really hot, no siezure problems though, i'm also running with a old AF lightened flywheel,i have two questions here really, when you modify the flywheel cowling to make it fit closer to the fan is there not a larger gap now between the flywheel cowling and head cowling, and can this gap be closed?Also the center peice of a flywheel cowling, the rings if you know what i mean, are these needed as i've seen quite a few scooters with this part removed is there a gain to be made from this larger opening more air getting in?One last thing if anyone has a picture of the modified cowlings could they post it if possible just so i'd have a better idea before i go butchering cowlings, cheers Hicksy.
If you lookat a standard cowling when it fits the correct flywheel the center holes line up with the very edge of the inside of the fins.
But the lightened flywheel runs inside this meaning not only is there a bigger gap but the hole in the middle is actually too large so the fan even after the cowling is fitted closer is still not as good as it could be,but alot better than it was.
If you have a donor cento or vega cowling welding the front of this into a modified cowling would if it was a tight fit shift even more air. But if you have a little sheet of metal it can be fabricated into a better more efficient cowling than just fitting it close as more of the fin area comes into play. As for the head cowl it needs to fit as snug as but don't beat it on the engine as theag housing lugs that hold it will probably snap.
Re: Cooling Lambrettas
Posted: Wed Sep 02, 2009 4:19 pm
by Snails
J1MS wrote:lammer205 wrote:
If you have a donor cento or vega cowling welding the front of this into a modified cowling would if it was a tight fit shift even more air. .
I wouldn't try to weld a Vega cowling as they are plastic.
J range are metal ones.
Re: Cooling Lambrettas
Posted: Wed Sep 02, 2009 6:18 pm
by J1MS
Snails wrote:J1MS wrote:lammer205 wrote:
If you have a donor cento or vega cowling welding the front of this into a modified cowling would if it was a tight fit shift even more air. .
I wouldn't try to weld a Vega cowling as they are plastic.
J range are metal ones.
ment to say Starstream, but I lost the plot all together, too busy thinking of Vega sized flywheel and Vega was much easier to write on my I Phone