LCGB Forums

Hello folks, have recently returned to the Lambretta fold after a short break (only 50 years). I have a '62 Li 3 125 which I would like to treat to a cheap upgrade. Back in the 60s we bored out to 175 and fitted an Amal. Very basic, but good fun and cost effective. I want to do something along similar lines, I've been given a 150 barrel and believe it or not, in the garage I found a brand new 62mm piston, still in it's box c/w both rings, gudgeon pin and circlips. Hoarder? Me? Make is GPM and Italian. So will bore out to suit this piston. I intend to use an SH1/20 carb and an AF Rayspeed Clubman. Now the questions....any comments re the make / quality of the piston, any comments re suitability of retaining the 125 gearbox, any comments on my intended conversion? Please, no "fit an Imola, Mugello, Casa " etc etc I don't have the finances for those. Thanks a lot, Mike.

If you're not going to tune the cylinder, why not just use a standard clubman? They make more power up to about 5000rpm.

Good luck.

don't forget to have the head re-profiled to suit the new piston/175.

I have this conversion on a gp and an li both originally 125. The gp has a scootopia clubman the li still
on standard exhaust . The gp does go slightly better but I am told it is a better engine power wise in the first place. I am swapping the gp back to standard exhaust while it isn't over noisy I prefer the standard exhaust note . Hopefully it won't effect the power to much. They both have the front sprockets changed to 17 tooth.

I would buy a 175 conversion head so you keep your old 125 top end in tact and a little porting work would help on the barrel your re-boring as for gearing you may have to change the sprockets but I would wait till you've run it in then see also worth considering is an electronic conversion

mikeyb1 wrote:Hello folks, have recently returned to the Lambretta fold after a short break (only 50 years). I have a '62 Li 3 125 which I would like to treat to a cheap upgrade. Back in the 60s we bored out to 175 and fitted an Amal. Very basic, but good fun and cost effective. I want to do something along similar lines, I've been given a 150 barrel and believe it or not, in the garage I found a brand new 62mm piston, still in it's box c/w both rings, gudgeon pin and circlips. Hoarder? Me? Make is GPM and Italian. So will bore out to suit this piston. I intend to use an SH1/20 carb and an AF Rayspeed Clubman. Now the questions....any comments re the make / quality of the piston, any comments re suitability of retaining the 125 gearbox, any comments on my intended conversion? Please, no "fit an Imola, Mugello, Casa " etc etc I don't have the finances for those. Thanks a lot, Mike.

Before you launch too hard into changes, you would do well to obtain a "Sticky's" manual as a good starting point. You might get the older version cheap or (even free) if place a 'Wanted' advert on this Forum.

If the piston is as intended for a 175 motor, then it will be a different compression height, unless it is a 'conversion' piston to suit bored out cylinders such as 125 & 150.

if you do hanker for more capacity, beware the 'cheap' kits available of Indian production. To make them serve any purpose takes many hours, & you'd be better to wait until a secondhand, fully sorted, larger capacity kit comes up for sale.

However, there's no reason that a 150 engine cannot perform very well on a budget. In the 70's, my GP150 kept up with most scooters of the time running it's SH2/22 but with a gutted, 'straight through' exhaust which wasn't too loud.

Gearing wise, you'll need a 16T or even a 17T front sprocket but shop around for chain. I've never bought from a dealer as 3/8" duplex is obtainable from any good power transmission stockists & will be far better than the Indian manufactured variety, which is stretchier than a Government promise....

As for reliability of the ignition, just check out this Forum, & you will see that points based set-ups win hands down there! It would be wise to convert to 12 volt, but there are far cheaper ways of doing so, & one method can be found on this Forum.

Thanks for all the advice chaps, to answer a few specific comments:
dickie, What's a standard Clubman? I thought there were standard exhausts and then the Clubman, which externally looks like a standard box but with a large cone added.
MickYork, sorry, should have mentioned the head, was intending looking for a good used 175 head.
Warkton Tornado, I bought Sticky's manual before I bought the scooter! Re the piston, thanks, am aware that I need a conversion piston, I'm hoping that that's what I've got, but have yet to investigate further. I do intend to stick with points, they were fine for all of us in the 60s, so they'll do me just fine. I do have electronic in my classic car, but I carry a spare set of points just in case. Cheers for now, Mike

Those old GPM pistons were never very good. Very prone to seizure on a thin walled barrel unless you're generous with the clearances and then they can be quite slappy and prone to skirt breakage.

Fast n Furious wrote:Those old GPM pistons were never very good. Very prone to seizure on a thin walled barrel unless you're generous with the clearances and then they can be quite slappy and prone to skirt breakage.

That's a shame, I was hoping to save a few quid, but thanks for the info.

mikeyb1 wrote:Thanks for all the advice chaps, to answer a few specific comments:
dickie, What's a standard Clubman? I thought there were standard exhausts and then the Clubman, which externally looks like a standard box but with a large cone added.

Sorry, you're right. There's no such thing as a standard clubman, I meant a standard exhaust.

Thanks for clearing that up dickie.