Scooterotica

I am looking for a heads up on what I'll need to build myself an RB20 engine. What top and bottom end requirements are needed, whats the best gearbox to use, best crank, best piston etc. Any info mucho appreciated in advance, so c'mon all you RB guru's spill the beans (please).

bryansmudge wrote:I am looking for a heads up on what I'll need to build myself an RB20 engine. What top and bottom end requirements are needed, whats the best gearbox to use, best crank, best piston etc. Any info mucho appreciated in advance, so c'mon all you RB guru's spill the beans (please).

Bryan, for what its worth I have a RB20 but I suspect you would have to ahve the same set up pipe & carb wise as well to do like for like comparison.

I initally had an Li150 box in which was gash and would not pick up in 4th at all, then tried Italian GP 200 but 4th was still an issue unless i was really high up the rev range. Finaly ended up with an indian GP200 box which has one less tooth. Now pulls in 4th both up hill and into a headwind. Have a 18x 47 set up with a 30m delly and an NK mid pipe. The crank is a race job from Tasffspeed, not sure about squish but can check if you want?

Sef

The Indian GP 200 4th. is the same as the Italian GP200 4th, its 3rd thats different, its closer to 4th.

SYD ...I cant believe that you ditched the LI 150 gearbox as all that was possibly wrong was your sprockets.....

Still have it, ready for the cutdown that one day may happen... plus i wanted to try and shorten the gap between 3rd and 4th and was told that the best box for that was the Indian. But then again im a novice...

Components like gearbox / sprockets and exhaust depend on your type of riding but taking into account that it's primarily a high revving engine that should still produce decent power as high as 9,000 rpm then I'd be looking at components that will bring the best out of the kit, like a close ratio gearbox (AF do one), Franspeed race exhaust, TMX35 or Dellorto 34, from there it depends on how deep your pockets are, £400 Alpha crank, £400 AF race clutch, Wiseco piston, etc..... Build it as bullet proof as you can afford.

corrado wrote:Components like gearbox / sprockets and exhaust depend on your type of riding but taking into account that it's primarily a high revving engine that should still produce decent power as high as 9,000 rpm then I'd be looking at components that will bring the best out of the kit, like a close ratio gearbox (AF do one), Franspeed race exhaust, TMX35 or Dellorto 34, from there it depends on how deep your pockets are, £400 Alpha crank, £400 AF race clutch, Wiseco piston, etc..... Build it as bullet proof as you can afford.

Totally agree.
I would advise Alpha crank, race tour piston (or the japanese RB20 piston), LTH clutch (i got sick of having a sore left arm and shoulder with my Tino six plate), franspeed race exhaust with carbon muffler (the lighter this piece is the longer the rest of the pipe will last IMHO), suitable carb, i use a mikuni but a well set up delly will work just as well and perhaps most importantly for reliability a LOW compression cylinder head. Gearing is up to you and how you want to ride. Take your time and get it built right.

Before you go weighing out £500 on an alpha cranks and 34 m carbs and race pipes with f**k off expansion chambers you want to ask is there a down side? And depending on what you want from the scoot then there could well be.

For a start a RB20 is one revvy baby even straight out of the box and the addition of a race pipe means you will be spending a lot of time in the petrol station and may want to consider buying BP stock while the price is down as you will be using sh*t loads of 2 stroke.. . I get approx 40 miles from a standard tank, with oil that’s pretty much £10 for 40 miles.....ouch. and that’s with a mid pipe not a race and with a 30m delly as opposed to bigger TMX. It’s also a pain to ride unless you’re in the power band which won’t kick in until higher revs.

So to sum up, if you are minted and love to drive everywhere at 100 mph and like to spend a lot of time on petrol station forecourts you want to have a think re the parts. For what its worth the 30m is fine and I like the look of Ads touring pipe for the rb which is out soon and has a more usable power range.

Sef


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Well i drove my RB22 from Ghent in belgium to Lincoln in England (Gent- zeebrugge/ hull- lincoln)on one standard lambretta tank of fuel, and even on long fast runs i was getting around 70 miles to a tank and thats with a 35TMX and franspeed race.
I thought the original question was for advice from people who had built and run one? all i did was list the spec that i use reliably (so far give or take the odd clutch!!) for around 3500 kilometers or so. If i wanted fuel economy and touring characteristics i'd buy a casa lambretta kit or something.

johnd wrote: If i wanted fuel economy and touring characteristics i'd buy a casa lambretta kit or something.

Exactly. The plan with mine is to build an engine for Street Class racing. That's about £5 per mile just in entry fees. I'll be building it as bullet proof as I can.