small block virgin

[wurzel]

I'm going to build a small block engine for my kid brother and like me he's not getting any smaller.
He doesn't want to change the original casing out to put a 200 in but he wants something faster than
the 125 motor that was in it when bought.I've got a 175 top end,22mm jetex and 42mm AF Clubman
lying around.The thing is the only gearbox that he has is the original Li125 with 15 tooth front sprocket
and I've got a 46 tooth solid crown wheel he can have.Would this set up work well enough in a series 3
mostly ridden one up and give him a descent cruising speed.

He doesn't need a balls out race machine just a useable scooter and he hasn't got the money to put a Casa,
GT186 or RT kit on it,also the original Li crank is in good condition but he would like to put an electronic
kit on for reliability.Would the crank be ok or would you swap it for a GP crank and if so what crank would
be sufficient for this set up.

Would appreciate any feedback

Regards Mark

[rosscla]

If you're not going to tune it to the hilt and simply up the cc to 175 if the original crank is actually in good nick then you should be ok.

You can get electronic kits to fit the the Li cranks which will be fine on a standard type kit.

[corrado]

15 x 46 with an Li125 will be screaming it's head of at 55 mph. 16 front sprocket, stretched 80 chain [or 81 chain and pulldown chain tensioner] would give it 5.3 final drive in top so it should cruise at around 50 mph and just top 60 flat out. It's what I started out with and performed ok for a while, in fact it was the best engine I've ever had for round town riding, trouble is that I started doing rallies on it and flat out all the time, hence it didn't last long and I'm only 10 stone.
Tell him to start saving for a decent kit. MB RT 195 kit with 17 x 46 gears should cruise closer to 60 and touch 70 flat out.

[wurzel]

Would changing the gearbox to an SX200 or Indian GP200 be a better option.
I've got a spare pull down tensioner and my serveta 200 gearbox that I pulled
out when I put my Cyclone in (was keeping to one side just in case) and also
got a spare 47 tooth crown wheel.

[Muttley McLadd]

Is it a proper 175, or a bored out 150?

A 175 can be taken out for more power.

I'd have thought that a 175 would struggle to pull 4.8 gearing. Especially if one is a bit calorifically challenged.

[corrado]

You need to play around on Tony Cassidy's gearbox visualiser ... download it here.... http://avantone.wordpress.com/ You can compare different gearbox set ups, you just need to be realistic with your power assumptions from a 175 kit with 22mm carb, it's not going to rev above 6,000 rpm. Taller gearing will IN THEORY give higher top speeds but in practice if you go too tall then it won't pull it and won't rev as high and end up giving you a lower top speed. Just because an SX200 with 8bhp could pull 4.8 gearing doesn't mean your engine can pull it. My 16 bhp Imola couldn't pull 5.00, I spent more time in 3rd gear.

[wurzel]

It's a bored out 150 so I'll take it there's not much more I'm going to be able to
do with it.
Starts to shed a lot of light on how much you spend when you've suddenly got a budget to
work to

[Muttley McLadd]

Realistically.. doing anything with a Lambretta with a budget isn't an easy task these days. And hasn't been for some while now.

[crooky]

I had an af 175 on my series 2 went well with a 16 front as said before I tried a 17 and it struggled. Was a good 50 odd plodder and good on hills. I've an li boss you can have if you need one.

[Chris in Margate]

Most cost effective route in my opinion is the universally tried and tested converson bore to 175 with the proper 175 conversion piston; 16 tooth front sprocket matched with the standard 46 tooth rear sprocket; stretched standard chain or new 81 link chain and tensioner; Clubman exhaust; upjetted carb (or fit a 22mm Jetex). Sounds good, runs good and the performance increase feels like 60mph and will show 60mph on the speedo but in truth it will be good for a genuine 55mph and under good conditions with wind and gradient it might get close to 60mph.
Stories of 2 up on this set up cruising all day long at 60mph are as accurate as a Lambretta speedo !