Yamaha RD50M – Engine

I pulled the RD engine this weekend and disassembled everything. Of course it will get new bearings and seals, the crankshaft is still very good, as are the gearbox and clutch. But the clutch has to go, it’s a two plate model, i will try and fit a four plate clutch from a DT80.

There will be some machine work done to the crankcase, as i will fit a cylinder from a Minarelli scooter engine. The gasket surface needs to be lowered 2-3 mm, the bore for the cylinder skirts will be enlarged and the transfer ports need to be matched.

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.

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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: