LCGB Forums

Want to up gear an LI150 as I have fitted a RT 190/200 kit, thinking of raising the front the front sprocket to 17t (I think 18t might be to much? ) from the standard 15t, does this sound about right, if so what chain will I need 81link or 82.

I most definitely would NOT go with either 17 or 18 front sprocket.
17T will give you a final gearing of 4.6:1 and 18T will give you a completely unrideable 4.34:1 final gear ratio.
Whilst the top speed calculations look exciting, in reality you will never be able to rev the engine that high.
A 16T front sprocket will give you 4.89:1 but you will need the right exhaust to reach maximum revs in 4th gear.

Thanks for that, I might go with the 16t then, to be quite honest I have not had much experience with small block motors and kits, would an 80 link chain go with the 16t sprocket, got a MB BGM big bore to go with it

A used 80 link chain should work with a 16 x 46 set-up

Thanks all

You'd be better off with an 81 link and a pull down chain tensioner. Though Martin was right in saying "used" ie, well worn and not "stretched".

I'm doing something similar,
I have chosen a 16 front sprocket with 47 rear using a new 81 chain,
30mm carb and a 50mm Gori.

MB had this on their Tech Site about RT kit gearing.. hopefully will help someone.

GEARING RATIOS

As with jetting it is so variable as we don't you the customer. There's loads to read in our Tech-Site on gearing. But what you need to think is how you ride? How heavy you are? Do you ride 2 up loaded? And how fast do you want to ride? Gearing which has worked for customers varies from 5.20:1 down to 4.3:1. If your not bothered about a high top speed but want power all the time in each gear regardless of road conditions and an easy ride - use something like Gp125 gears with Gp200 sprockets 18 x 47 which is the same as Li150 Italian gears with standard sprockets 15 x 46. All the kits pull this gearing easy, it will limit top end speed but makes a really nice ride-able engine especially if your a big person or you constantly ride 2 up.

If you want more top end speed and through the gears increase the sprockets to get around a 4.80:1 gear ratio, which is a Sx/Jet200 gearbox with standard sprockets 15 x 46. If you set your motor correctly the RT kits have power to pull 4.3:1 which is the Gt/Tv200 gearbox with 15 x 46. Larger carbs produce more power, these help you gain power through the rev range. Have a kit tuned or especially Reed valve converted and expect to increase the gearing quiet alot to really feel the benefit of the kit.
http://www.lambrettaspares.com/info/setting-up-*-engine-carbs-2-/setting-up-*-cylinders-mbgm-rt+255.html