RB improvement

[MilanoMod]

I’m running an RB22 and it has performed wonderfully so far. I’ll be stripping the scoot down for paint and while I’m at it would like to give my top-end a look over, maybe even improve it.

1) I keep hearing RB reeds hit it the cylinder. Should I be grinding a certain area down in the inlet to prevent this? If so, where exactly?

2) Is there anything I can do to get even more power out of the kit? From reading here it sounds like certain pistons don’t let transfers blow right out the exhaust, should I switch from the stock Asso? Would putting a 60x110 crank help a lot with power? If so, should any of the ports be altered? Running an NK road pipe at the moment.

I’m in the US so dropping by the local performance shop isn’t an answer. I’m comfortable doing minor porting.

[Warkton Tornado No.1]

If the reed petals are causing an issue by hitting the piston, then packing the manifold from the barrel may be the solution. I am unaware of a more compact reed assembly to suit, but you may find them more easily Stateside. Packing may necessitate eccentric cones.

The crown of the piston relative to ports is controlled by the stroke & rod length. A piston with exactly the same compression height with a flat top will exert the same exhaust & transfer port timings as a radiussed top. Other reasons may have you consider an alternative piston from the aspect of strength & even cost. If building any 'enhanced' Lambretta engine, the Lambretta specific pistons as you have fitted now, or even those made for & sold by Lambretta tuning emporiums are the last that I would consider whilst OEM pistons for Honda, Suzuki, Yamaha, Polaris etc & Wiseco (of course) exist that can be fitted. Just make sure that the ring peg positions are alright (easily 'moved') & the ring material is compatible.

[Warkton Tornado No.1]

If the reed petals are causing an issue by hitting the piston, then packing the manifold from the barrel may be the solution. I am unaware of a more compact reed assembly to suit, but you may find them more easily Stateside. Packing may necessitate eccentric cones.

The crown of the piston relative to ports is controlled by the stroke & rod length. A piston with exactly the same compression height with a flat top will exert the same exhaust & transfer port timings as a radiussed top. Other reasons may have you consider an alternative piston from the aspect of strength & even cost. If building any 'enhanced' Lambretta engine, the Lambretta specific pistons as you have fitted now, or even those made for & sold by Lambretta tuning emporiums are the last that I would consider whilst OEM pistons for Honda, Suzuki, Yamaha, Polaris etc & Wiseco (of course) exist that can be fitted. Just make sure that the ring peg positions are alright (easily 'moved') & the ring material is compatible.

[MilanoMod]

Thank you!

I don’t know that the reeds are hitting the piston, I thought I read that the corners are hitting the barrel inlet somewhere.

I don’t know that I want to reinvent the wheel looking for a piston, l was hoping that someone had tried one that didn’t have the faults of the Asso.

I suppose what I’m really after is DIY in the mold of one of the TT kits. It sounds like he’d prefer to sell them locally so he can service them. The recipe seems to be longer stroke RB (possibly monoport exhaust and blocked boysen feeds, not sure), inlet cleaned up to avoid reeds and improve flow, exhaust raised to compensate for stroke and rod’s affect on transfer timing, an Avanti or mammoth head, a fat copper head gasket, CHT gauges and remote choke, Avanti Ex box, short manifold to allow full filtration under panel, and perhaps variable timing. This would lack any of TT’s special tuning but if I got 30-35 reliable hp out, starting sooner in revs, I’d be happy. You’d think there’d be instructions in this forum but maybe the UK has so many shops depending on making these type of setups that it would hurt financially. Hence my desire to try to come close on my own.

[Warkton Tornado No.1]

I don’t know that the reeds are hitting the piston, I thought I read that the corners are hitting the barrel inlet somewhere

.

Sorry! My mistake in misreading your Post. I'm not aware of the reeds fowling anywhere.

I don’t know that I want to reinvent the wheel looking for a piston, l was hoping that someone had tried one that didn’t have the faults of the Asso.

I would be nervous of using the piston that comes with the kit. Before now, I have asked Forums for any verification that the DT250 piston is/was being utilised in 70 mm bore reed valve cylinders. No responses were received so I went ahead anyway with a non Dykes ring Mitaka piston. I re-profiled a heavyweight SIL head to suit the piston & fitted it to the TS cylinder with a 60 mm stroke. Inevitably, I ported the kit as it had a MAHOOSIVE slot on the intake skirt & a smaller slot on the exhaust skirt after throwing a rod. Fortunately, I am of the opinion that increasing case volume is a good thing, so it now communicates directly with the port running through the inlet port.

All the transfers & the 'boost' transfer are the same duration. The boost is one, large slot as I moved one piston peg rather than fanny around to make fingers.

If I were to do the build again with a written off cylinder, the only thing I would change in the process would be to go for even more stroke @ 62 mm & probably add supplementary exhaust ports for the pulse benefits.

Before the build, the 66 mm x 58 mm TS was reputed to be making "over 30 BHP" so I hoped to match that. The only test has been via the owner's "seat-of-the-pants-dyno" but he claims this engine is far stronger & more powerful. He used to run an RB but reverted to TS because he didn't like the manner in which power is delivered via the RB. He certainly wasn't scared of it, but found it hard work.

I suppose what I’m really after is DIY in the mold of one of the TT kits. It sounds like he’d prefer to sell them locally so he can service them. The recipe seems to be longer stroke RB (possibly montoport exhaust and blocked boysen feeds, not sure), inlet cleaned up to avoid reeds and improve flow, exhaust raised to compensate for stroke and rod’s affect on transfer timing, an Avanti or mammoth head, a fat copper head gasket, CHT gauges and remote choke, Avanti Ex box, short manifold to allow full filtration under panel, and perhaps variable timing. This would lack any of TT’s special tuning but if I got 30-35 reliable hp out, starting sooner in revs, I’d be happy. You’d think there’d be instructions in this forum but maybe the UK has so many shops depending on making these type of setups that it would hurt financially. Hence my desire to try to come close on my own.

You probably need to think things through. Have a chat with Ben @ Rayspeed, especially about any exhaust port issues. Personally, I like wide, bridged ports & they work well in the old cast iron barrels.......

Not had head problems other than in the 70's since when I have never used a gasket. The squish must always be optimised, the head or barrel preferably spigotted & the CR sensible. Super unleaded fuel is mandatory.

Box exhausts. Hmmmm. I run one with an inch out of the side to give ground clearance, fully rubber mounted, l - o - n - g reverse cone, one inch bore bleed & a silencer. The 'U' pipe is as short as it can be & spring connects to the 'box' The pipe is only 38 mm, but works well, though I have others to try. BTW. This is a 71 mm x 61 mm Rapido. It works very well & pulls unfussily from town speeds to WOT in fourth (TV200 equivalent) But, is it a "box exhaust" anymore? I will be making a replacement soon as it suits that engine configuration & the style I wanted. Would I stifle an RB engine though, with the same? No. Would I investigate similar configuration engines (KTM?) & source an expansion chamber as a basis with modifications to the cones? Yes.

Filtration needs to be of adequate size, specifically the 'plumbing' if remote. Some carburettors are more filter friendly than others. I've been extremely surprised & pleased with the PWK's that OKO & the like sell, even though I must have a dozen or so Dell'Ortos. You have a wide choice where you are though.....

As for ignition, fully programmable systems are available, again from motorcycles, than can be made to fit. Plastic fans from the autos are super strong.

[MilanoMod]

Ended up going RB252. (Monoport RB25 w/62x118 crank).

Very pleased with the kit and and with Darrell Taylor, who needs an admin assistant so he can leave off answering endless “is it ready?” and fitment questions from punters like me.