Author Archives: Carsten Lorenzen

Yamaha RD50M 1979

A new project again. I’ve had this Yamaha RD50M for a while, and no plan for it. It’s a german 5 speed model, it can never be ridden as a Moped in Denmark. What better to do than a tuning project?

Right now i’m stripping it for parts that i don’t need, less weight and fewer parts that can fall off 😉

The engine will get new bearings, seals and some porting for a larger cylinder kit. At the moment it has a 45 mm Polini kit with a 20 mm Mikuni. A good daily driver with a topspeed of 80 km/h, nothing you can win a race with. I need something faster, more about that later.

The gallery will be updated with more pictures in the future.

Polini Evolution Engine

I got another engine for my Piaggio mopeds, a Polini Evolution engine. I have no plan for it yet, but since i got it for a good price, i bought it for future projects.

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I could only find an italian manual, so i used google translate to make it understandable. I only gave it a quick cleanup, so expect a few weird sentences 🙂

Download the english manual here:

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Polini Speed Engine

Next Vespa Bravo upgrade, a Polini Speed Engine. A very nice engine case with enlarged intake and bored to accept 46 mm cylinder kits. Nothing you can’t achieve on a stock engine case, but i got it for a good price from my friend Nikolaj.

polini-speed-engine

I bought a special intake manifold from Italy, made for a 15-16 mm SHA instead of the normal Piaggio SHA 13 mm carburetor.

I mounted the engine with a used original crankshaft, new bearings and seals. The intake opens 130° before TDC and closes again 51° after TDC, giving me a total duration of 181°. Good for many of the cylinders that are out there.

The setup will be:

  • 46 mm Polini cylinder kit
  • Dellorto SHA 16 mm carburettorchanged to 13 mm
  • Proma Circuit exhaustchanged to Sito
  • Polini variomatic – changed to non-variated

Stay tuned for future updates!


Last update, the Bravo is done for now, onboard video:

Kreidler 3 speed engine repair

A local guy brought me this engine, he bought it restored many years ago, but didn’t use it much. The changing temperature differences gave condensation in the engine case and caused a lot of rust damage. The oil was brown and very thick like mayonnaise.

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I changed the damaged parts, did some machine work to worn bushings and rebuild the engine with new bearings and seals.