Scooter Review: The evil twin
By: Sarah Wilkinson
Dave Briggs is no stranger to these pages; we’ve featured his auto engine hybrid Lambretta Vega, ‘Lunacy’, plus a road-going twin cylinder Lambretta auto ‘Twin Peaks.’ He’s been busy in the garage improving things to try and make this latest home-built twin cylinder engine a bit more useable.
Piaggio didn’t design their feisty little two-stroke auto engine to run two Malossi 172 cylinders and put out over 46 horsepower and there are a few components that don’t particularly like having all that extra power thrown at them. The actual crankcases have always been a bit weak, the later type (identified by the black cover over the external nut at the rear of the casing) were modified by Piaggio and they are a big improvement, so Dave opted to use them for this scoot. He’s also made a rear strengthening brace, (with his initials cut into it) to help protect the engine and so far all is well. The belts don’t like spinning quite this quickly either and the crank (or should I say cranks) really are the weakest link.
It takes two new cranks to make one twin opposed crank for one of these engines and Dave has spent a fair few quid trying different techniques to make the mating process more reliable. For this engine, the long stroke cranks were joined by a male and female six-sided spline (which is turned down). The cranks are drilled out, splines pressed in, then welded inside and out to strengthen things. Obviously the casings have to be a bit wider to accommodate two barrels, pistons and cranks, so Dave uses two sets of damaged casings (damaged casings are used to cut costs) and a 70mm packer plate to help centralise the rear wheel. To keep the power under control, the rear end is hung on a pair of shocks, as opposed to the usual single item - quite advisable when you’ve got a 364cc two-stroke motor to harness. The ignition system is something else to consider when you build a twin; you need to use two CDI units, two coils and two pickups, so it can start to get a tad expensive. Team Dwarf Racing at Wellingborough built those lovely exhausts for him and the engine was set-up at auto tuning specialists PSN Scooters in Batley.
Dave has done his research into running a twin cylinder auto the hard way, through trial and error. He wanted to be the first to build a road-going machine and (as far as we know) he succeeded with ‘Twin Peaks’, a scoot that has since been sold on and improved by the new owner. This latest attempt has seen Dave trying new techniques to overcome the crank and belt problems which caused his first motor to be a little bit temperamental and so far it’s looking good. Whether it will ever be a practical day-to-day scoot is too early to call (rumours of a production run of twin cranks from PM would certainly improve things), but when you’re pushing 46bhp on the road in such a light chassis, it’s never going to be a sensible means of transport and while the engine is running it’s great fun and more exciting to ride than any two-stroke you’ve ever ridden.
The donor frame for this project came from a Purejet 50; he had to modify the engine mounts to accommodate the new engine. He’s also turned the oil tank into a fuel header tank to try and solve a slight fuel starvation problem which showed up at just short of a ton up on the Dyno at PSN when they set it up.
Aesthetically, the stock panels were replaced with an Evo bodykit and given a simple, but effective, yellow spray job and a few vinyl cut graphics. Add a bit of polishing and chrome and it’s enough to make you look twice at the scoot when it’s at a standstill. With the motor running you don’t need an excuse to look at it though; the machine sounds like an angry chainsaw and its power is more than enough to pull down a mature oak!
The scooter was finished and road-legal just in time to receive a runner-up prize (no pun intended) at this year’s Isle of Wight Custom Show. So will Dave be putting his feet up over winter - what do you think? He’s already got an air-cooled twin engine almost completed which will go into a Lambretta frame; he’s also planning a Vespa auto and has a whole host of other projects and crazy ideas lined up, so don’t think this will be the last you’ll see of him.
If you want to own a unique road-going scoot, give Dave a call - he may just part with this scooter to enable him to carry on with his ‘research.’ You can contact him on 01472 371253 or 07786 650101.
Words and main photos: Iggy
Engine photos: Dave Briggs
Responses to “Scooter Review: The evil twin”
Current Issue: Nov/Dec 2015
• Next issue on sale: 16th December 2015