Scooterotica

Why is there a new crank for the RB20? Why don't they use the one AF has already for the RB22? Or why not use this one on the RB22? What's the difference?

Don't tell me there's a 3rd one for the rb25?

a 58mm crank is used for the RB22

RB25 uses a 60mm crank

Different conrod - 116mm (same as the TV175).

I think in order to bring the cc's up to 200, it uses a 65mm bore + longer conrod to make it about 198cc's? Someone correct me if I'm wrong?

The piston has a low compresion height on the RB20 so a long 116mm con rod is used (like on the TV 175).
Conrod length has nothing to do with CCs ,its crank stroke and piston size that give you that.

CPH Lambretta wrote:The piston has a low compresion height on the RB20 so a long 116mm con rod is used (like on the TV 175).
Conrod length has nothing to do with CCs ,its crank stroke and piston size that give you that.

Correct ...Top of the class....I was told the Pitons 9mm shorter, and the rods rods 9mm Longer to make up for this....

im sure the lenght of the conrod has nothing to do with cc,s its the stroke that decreses ot increases them

To help...

1) Rod length has nothing to do with cc capacity
2) Stroke (58, 60, 62 etc) will change cc capacity
3) The RB20 uses a piston based on the Yamaha blaster piston, its compression height is less than the standard Lambo piston.
4) Compression height is the distance between the centre of the gudgeon pin and the edge of the piston, if i recall correctly a standard lam piston is 39mm from edge to pin, and a Yam Blaster is 30mm.
5) To compensate for the shorter comp height on the piston, the RB20 uses a 116mm rod instead of the 107mm on a standard Lambo
6) 107 + 39 = 146 & 116 + 30 = 146
7) A 116mm rod gives additional tuning benefits such as a 2:1 rod/stroke ratio (58mm stroke x 2 + 116mm) and helps reduce piston rock
8) Consumers maybe unhappy at not being able to use a standard 107 rod on the new kit, as it means additional expense....but it is a better rod/piston combo than 107/39.

Do you think that if they were starting from scratch that they'd of found a piston to suit 58 x 116 for the 225?
Is anyone using such at set up and if so which piston?

Oh, and is anyone using a 60 x 116 in the RB20?
Does anyone know if the 60 x 116 would be a good upgrade for a track / race engine?

If you can get a trade catalogue off Grampian motors ( Grampian motorcycles, Musker st, In Crosby) , as the old catalogue used to quote all dimensions of pistons, year, models, conrod dimensions, width & length of small end I.D. and big end I.D. and probably more than a hundred pistons listed... The catalogue I have dates back to the late 80s if you get in touch with them ask for John hes usually very helpfull and has a wealth of knowledge ........ A word of warning .... He dosnt actually like Lambretta's but loves 2 stroke engines....

They used to have a couple of racing bikes in the old shop, a Yamaha tzr and some other Yam 2 stroke....they used to give me so much stick when I took my old Lambretta barrels and Cranks in to be bored or pressed....Then I realised why he gave me so much stick when I had my first ride of a Twin cylinder 2 stroke Jap bike ... Jesssuuuussss!!!!! were they fast....