Precision engineering? ‘That looks about right.’
Precision engineering? ‘That looks about right.’

 

“Putting a Vespa engine in a Lambretta? That’s a hanging crime in some States mister…” Yeah, like Scooterboys young and old give a shit about your opinions.

 

This is the long-awaited edition where we finally perform the unholy matrimony, in a bid to combine the economy and performance of a home-tuned Vespa smallframe motor with the lightweight lunacy of Bertone’s Lui chassis.

 

Engine Fitting

 

Those who’ve followed this story since the outset (if not, read back to parts 1, 2, 3, 4 and 5) will remember that we set ourselves a particular task. It’s not tricky to fit a Vespa engine into a Lui using a fabricated and welded bracket, but we wanted to develop a conversion that could be carried out with the minimum of disturbance to the original chassis. Ideally, this would actually mean zero chassis modifications by developing a fully-reversible conversion using a bolt-in engine bracket.

 

Engine bracket MK1
Engine bracket MK1

 

Where to start?

 

The starting place was initially pretty simple; balancing the Vespa engine beneath the Lui chassis and experimenting with angles and taking measurements. The first decision was to try to maintain the original Lui wheelbase, even if that meant raising the rear ride-height slightly. A jacked-up back end is no problem for us because we plan to replace the front forks with something less liable to bend in a stiff breeze than the original pressed steel Luna forks.

 

With the engine balanced in position we noticed a joyous harmony. Unlike Li-series Lambrettas, the Lui engine mount is centrally positioned either side of the centre-line of the wheel. Happily, the same is true of the Vespa smallframe engine; even if the engine mount is much wider. Thus our prototype welded engine bracket could be utterly simple; a horizontal piece of box section steel with two metal brackets going forward to meet the Lui chassis, and two wider-positioned ones going back to meet the Vespa engine.

 

‘Zip zip’ said the ginder. ‘Gzzzg gzzzg’ said the welder. Bosh!

 

The prototype engine mount bracket takes shape. It’s not pretty but we learned a lot.
The prototype engine mount bracket takes shape. It’s not pretty but we learned a lot.
Changing the engine bracket angle alters the wheelbase.
Changing the engine bracket angle alters the wheelbase.

Mocked and loaded

 

The mocked-up bracket revealed a couple of things worthy of note.

 

The first was that if you changed the angle of the bracket where it was bolted to the Lui frame then it altered several factors:

 

  • Swinging the bracket altered the wheelbase of the machine
  • Moving it also altered the clearance between the exhaust downpipe (as it exited the barrel) and the spring of the rear shock.
  • Rotating the engine bracket also altered the ride height of the rear of the machine.

 

Bring in the professionals

 

The other issue that immediately became apparent was that I wasn’t entirely happy about the main connection between engine and chassis being a welded joint between two different pieces of steel. I trust my welder and welding to a certain extent, but I’d always prefer to make a joint as important as this out of one piece of material if possible.

 

This desire for simplification drove me to see my friend Phil the Engineer with prototype in hand and a beer-mat sketch of what I wanted making. Amongst the many medieval torture devices in Phil’s workshop is a massive hydraulic forming tool capable of bending, crushing and slicing thick sections of steel like Plasticene.

 

I wanted Phil to drill and bend some 6mm-thick steel bars with shallow angles so that they could form left and right-hand connections between engine and chassis. Then, all that would be required would be a weld-in a connecting piece to make sure both sides always remained parallel. This system meant that all the factors mentioned above could be altered simply by adjusting the position of the bracket.

 

Folded steel plates make a much safer form of bracket.
Folded steel plates make a much safer form of bracket.
The jig we knocked-up to hold the brackets in position while the centre-bar is welded in.
The jig we knocked-up to hold the brackets in position while the centre-bar is welded in.

 

Bad Vibrations

 

We had two options at this point. We could mount the Vespa engine solidly to the bracket and have the whole assembly pivot on the Lui engine bolt. Alternatively, we could fix the bracket rigidly in position and let the Vespa engine pivot from it exactly as it would in a Vespa frame.

 

We chose the second path for one very good reason. Vespa engine mounts work. They let the engine swing without transmitting tons of vibration into the chassis. The Lui system on the other hand was famous for not working very well, except as an entertainment device for Nuns.

 

Mk2 engine bracket, now with box steel crossbar and rounded ends.
Mk2 engine bracket, now with box steel crossbar and rounded ends.

 

Fixie

 

With all these factors now established it became obvious that what we really needed was some way to set the angle of the bracket in relation to the frame. Ideally something that wouldn’t require any frame modifications, but would be adjustable.

 

I began dreaming up all sort of elaborate and ugly threaded rod solutions between the engine mount bracket and the frame. We were lucky that on this particular version of the Lui there was a small bracket for the HT coil under the frame, roughly in the centre of the fuel tank. This bracket, no matter how weedy-looking, should hopefully be enough to make a top mount for some sort of ‘angle adjuster’.

 

If only I could find a tidy solution…

 

How do you find one of these if you don’t know what it is called?
How do you find one of these if you don’t know what it is called?

 

EvilBay to the rescue

 

Whenever I come across situations like this; where you have something in mind but don’t know what it’s called, there are two modern tools that prove invaluable: Google and eBay.

 

The first step is to try to describe what you want – i.e. ‘threaded rod adjuster’ in Google and then look through the Images tab for the closest thing to what you want. Then after you’ve found out what the rest of the world calls this device you can hone the description until you have a term that you can put into eBay.

 

With eBay again having almost everything in the world on sale, and being image-based, it’s not too tricky to find what you want.

 

It turned out that what I wanted – as a tidy, adjustable solution to fix the angle of Sam’s engine bracket – was called a ‘turnbuckle’. As soon as I had that term then I could find the type of turnbuckle that we needed.

 

The type I settled on was originally intended for tensioning rigging, fencing or thick wire cables. Essentially it’s a thick stainless steel tube threaded at one end with a right-hand thread and left-hand thread at the other. Into this screws two threaded eyes (or sometimes hooks) with lock-nuts. In use, you can bolt it in position through the two eyes and simply adjust the overall length by twisting the central part. The type we ordered from eBay was made from stainless steel with an eye at each end and cost £7.95 delivered. There’s no way that I could make something as tidy or effective for that money. Why try to reinvent the wheel?

 

Sam made some simple steel plate brackets to bolt the turnbuckle to the HT coil mount on the frame, and similar brackets to weld to the cross-member of the engine bracket at the other end.

 

Hey presto, a super-strong but adjustable Vespa engine mount for a Vega with zero frame modifications required. When we’ve tested it we might even put a few into production as a kit for anyone who’d like to do the same conversion.

 

Handmade brackets for the turnbuckle bolt to the HT coil mount on the frame.
Handmade brackets for the turnbuckle bolt to the HT coil mount on the frame.

 

It’s a shocker

 

For all the majestic tidiness of the front engine bracket, the rear shock mount is a bit more Heath Robinson.

 

Again, figuring that Piaggio knew what they were doing with the suspension and vibration elimination of the Vespa smallframe we chose to use a standard smallframe rear shock as well as the big rubber silent-block that normally attaches to the chassis. A simple welded construct allowed this to slip onto the rear shock stud sticking out of the Lui frame. I’m sure this is something that we’ll improve given time.

 

Using the adjustment on the engine bracket we were able to get a working gap between the exhaust and the shock. This all looks like it might even work…

 

To be continued.

 

Words and photos: Sticky

 

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