Fitting Lambretta’s best lightweight scooter with Vespa’s finest 2-stroke engine.
If you missed Part 1 of this series, then you can find it here.
I’m not expecting anyone to use this article as a blueprint for building their own smallframe engine because the parts we are using are so incredibly disparate. This is more an exercise in using odd bits gathered over the years that would otherwise sit unused in boxes in my garage.
Well, let’s start with the cylinder kit chosen. I literally found that in a bin.
The barrel is an old 1980s Pinasco 125cc reed-valve kit that I’d never previously even seen before. It was never imported to the UK to my knowledge.
The bin was outside a Vespa workshop that we found by accident in the mountains of Italy on a ride from Rimini to the legendary Elba scooter rallies.
I picked up the cylinder out of interest, expecting to find scored Nicasil or a damaged piston, but all the parts including the head and inlet manifold were all in usable condition. Only the single-ring piston has some light scoring.
Through Dean’s translation I asked if I could buy it, only for the mechanic to tell me that I could take it because it was rubbish. He’d taken the kit off a customer’s bike and fitted a far more powerful Polini 135 to replace it.
One man’s rubbish is another man’s gold.
In the 80s I was a bit fan of Pinasco parts, running their 225 kit on my Rally 200 (chopper) for a couple of seasons. Andrea Pinasco’s focus at the time was to improve on standard parts in terms of quality but only slightly in performance.
This reedvalve barrel followed the same pattern. In terms of a casting it is beautiful: die-cast with great quality plating. It has five transfers and a single exhaust port like the Polini so the potential is quite good. It’ll never perform like the new reed kits from Falc, Quattrini, Pinasco, Polini, Malossi or Parmakit, but you don’t tend to find those in bins. If we need more power we can always upgrade later.
What lets the kit down is the porting and the piston. The standard single-ring piston is only 55mm for 125cc when the Polini and Malossi are 57mm bore giving 135cc. Worse than that, is that Pinasco layout leaves the piston never fully opening all of the ports at Bottom Dead Centre (BDC), much like a standard Vespa barrel. I couldn’t tell how modest the original port timings were, but I’d be surprised if they were any greater than standard.
No wonder the dealer thought it was junk. You’d be upset to spend a lot of money on an expensive alloy reedvalve kit only for someone with a cheap cast iron Polini to blow you into the weeds.
I didn’t have any idea what I was going to do with the barrel but it was too good to leave in the trash, so I took it with the dealer’s blessing. It’s been in my garage for over 15 years…
Production Class Casing?
In 2016, at the outset of the BSSO Production Class, I had an idea to tackle the Lambretta dominance of the category with a smallframe Vespa. Initially the rules were written to allow Vespa smallframes and Large-frames to compete against the RB20 Lambrettas, but not really on an even footing. None of the bolt-on reedvalve cylinder kits were initially approved, so if you wanted to race a Vespa then it meant fitting a rotary inlet kit. The rules meant we could modify the inlet port but not weld it up.
Of all the smallframe standard casings the 3-stud inlet PK XL 125 has the best potential inlet port so when I was passing Darrell Taylor’s place once, I asked him to match the casing to a cast MB smallframe inlet manifold. What became quickly apparent was that there was no way to get a big enough inlet port without breaking through the casing into fresh air. If the casing around the port was welded, even to repair where it was broken through, then that would be cheating. With a maximum predicted power output of around 15hp, even with an illegally repaired casing, the project was a non-starter and shelved.
So that’s where the casing comes from.
As an aside, the Production Class rules have since been adjusted to allow Malossi’s latest reedvalve smallframe kits; which allowed Dave Delaney to be competitive on a smallframe, while the large-frame Vespa rules have also been tweaked to allow Mad Dog McKenzie to even win races on a large-frame Vespa. In my opinion if all the different types of hand-gearchange scooters can be accommodated evenly, so different types have different advantages depending on circuit, then it makes for a more interesting championship.
Core to the original idea of racing a rotary inlet engine was having the best crankshaft possible within the rules. Again this was complex but Denis from DRT was good enough to help with the project. He supplied a 54mm stroke drive-side crankweb and a long 105mm billet con-rod. Sadly because of the PX-style flywheel bearing used by the ETS casings he had no flywheel side crankweb to match, so a full-circle one for reed motors was sent and we’d have to get the crank assembled in the UK. That’s not a problem when you have the likes of Harry Barlow on the doorstep.
Another failing of the original Pinasco kit is that the piston has a full skirt on the inlet side. That kind of missed the point of having a reed-valve. Normally reed-valve pistons have holes in so that the inlet can flow whenever pressure dictates.
Thankfully, Dan from Vespa paint and body specialists Total Revamp managed to locate an oddball New Old Stock 55mm Malossi single-ring piston which had a large hole in the skirt on the inlet side. On the down-side the piston has a much shorter compression height (the distance from the gudgeon pin centre to the crown) than the Pinasco one.
Long Stroke Advantage
The crank I had from DRT was 54mm stroke, compared to 51mm stroke for standard. 3mm longer stroke effectively that means that the piston rises 1.5mm higher and drops 1.5mm lower on each crank rotation. That could be useful in obtaining some longer port timings.
Having a piston with approximately 5mm shorter compression height would be more than compensated by the crankshaft having a 105mm con rod instead of a 97mm rod as standard. Effectively the piston would end up sticking out of the top of the barrel if just bolted down. What would be required was an aluminium base packing plate to set the ports at the right height. The resulting question, like watching a Jerry Springer show, was “how thick”?
With Harry Barlow’s useful mantra of “to measure is to know” ringing in my ears, the only sensible solution would be to assemble all the parts as a dry build and use a selection of spacers to calculate it all properly.
I’ll show you how we did that next time.
Words & Photos: Sticky
NEXT TIME – We look at juggling the mismatched bunch of components to get our port timings right.
Project SuperLui gallery part 2
New products always in development…