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.
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.
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.
I changed the damaged parts, did some machine work to worn bushings and rebuild the engine with new bearings and seals.
I thought i didn’t need more mopeds for now, but then a old friend messaged me. He had this Vespa Bravo that he couldn’t get done. Everything was disassembled, engine and everything. The price was ok and included delivery, so i felt it was my duty to save this (once) fine Moped.
My first plan was to assemble everything as is, but the paintjob is just terrible . Everything is sprayed over, it needs a new paintjob.
The engine got a quick cleanup, new bearings and seals. The crankshaft was a bit abused, i’m giving it a chance. I’m running a original cylinder, the inlet timing and restriction are modified a bit. Just enough to pull a grown man, no racing engine… yet!
More information is found in the image descriptions, i will update the galleries with additional pictures when i get more work done.
To get better acceleration on my Puch Maxi, I adjusted my clutch to engage later at a higher engine speed. There isn’t much bottom end in the Airsal kit, with a heavy gear ratio it needs to build up some RPM before take-off.
I started with some stiffer springs, with as much preload as possible. Then i took about 12 gram weight of every clutch shoe. I ended up taking it down to 73 gram before i was happy with the result. I wouldn’t mind making them even lighter. Remeber to get an even weight and spring adjustment on all shoes.
I haven’t used my Puch Maxi in a long time, the aftermarket wire rims and cheap tires had a bit of vibration and the engine lacked power. I bought some Grimeca cast wheels and nice Schwalbe tires. For the tuning i got a new engine from my friend and club member Esben, don’t want to race the original number match engine.
I rebuild the spare engine with new bearings, seals and a stuffed DMP crankshaft. The topend is a 45 mm Airsal 4 port cylinder with a DMP head, the head isn’t designed correctly, i will need to make some adjusting. I started with a 15 mm Bing replica, but liked the 12 mm original square Bing more. The exhaust is a Jamarcol straight pipe, doesn’t make much noise and has pretty good performance. I need to adjust the clutch with lighter shoes and stiffer springs, there is not much bottom end in this Airsal kit.