Yes you read that right. 407cc for Vespa and Lambretta…

Just when you thought that it was safe to get back in the water… a new monster arrives.

We’ve been tipped off about a new kit that should take the air-cooled single-cylinder Vespa and Lambretta engine layouts over the 400cc barrier.

Italian overbore engine specialist Egig is currently machining a batch of air-cooled scooter cylinders that not only fit the BFA engine casings for Vespa largeframes but can also be adapted to crankcase-reedvalve induction Vespa smallframe motors (from the likes of Fabbri) and Lambretta engine casings like the CNC Killercase.

Presumably, it will also be possible to adapt it to other crankcase reed induction cases like the GT Intercontinental, KR Automation and modified CasaCase as well.

The sand moulds for casting Egig Zero-G cylinders
The important dimension required is for the crankcase mouth to accommodate the 105mm diameter spigot to a depth of 25mm; along with the correct layout for the four studs to fasten the cylinder down.

The intended configuration is a relatively modest 64mm stroke combined with a humungous 90mm Wössner piston that weighs almost half a kilo. Yes, that will definitely require a specifically-balanced crankshaft. At least if you don’t want your eyeballs to fall out of your skull while riding.

At the moment the cylinder has not been fitted to a Lambretta casing but we can expect there to be a few challenges on the way: not least of all in exhaust design thanks to the long 4-bolt exhaust outlet placing the downpipe very close to the floor.

A Zero-G 407 mounted in a lathe for machining
The specifications for the kit are very impressive:

• Suitable for BFA306 engine block and its crankshaft with connecting rod or the KillerCase for Lambretta from MMW
• 90mm bore
• 64 mm stroke
• 500g Wiseco piston with 18mm gudgeon pin diameter.
• Transfer timings of 122 ° to 130 ° depending on the positioning of the cylinder with packing plates.
• 30 ° blow-down (decreases with increased stroke)
• Cylinder head with 10-point fastening and a choice of 10.5: 1 / 11.5: 1 / 12.5: 1 compression at 1.3mm squish
• Exhaust is via a large main port and two very wide sub-ports. Included is a 4mm diameter decompression hole to permit easier starting.
• Cylinder plating by Monardi

Triple exhaust port layout with decompression hole to aid starting,
Anyone who is expecting this sort of engine to be a truly practical proposition for rally use in a Lambretta chassis needs to have a little head-wobble. I’m not sure practical is really the point of the Zero-G; particularly when Egig makes statements like “your penis will immediately become 5cm longer.”
Test-fitted to a set of BFA casing. As if 305cc wasn’t big enough…
Admittedly, Egig doesn’t mention the level of inflation required for initial measurement, so perhaps that’s not as unfeasible as it sounds, at least after a swim in a cold lake…

Even Egig admits that he considers the Zero-G as the ‘Mount Everest’ of single cylinder scooter kits: the last peak to climb.

What is at the top of this particular mountain you ask? In early testing on a Vespa it has already exceeded 60hp but not in a peaky way that required the use of a Sherpa and climbing ropes. This graph looked like a rolling hill that you could cycle up if you hadn’t eaten quite so much during lockdown.

We’ll be following this project closely at SLUK.

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