I have got a Worb 5 Polossi cylinder and after having major problems with the Malossi pistons ( x 2) seizing I have had the barrel rebored to accept a 2 ring 68.8mm Polini / Asso piston. I am going to run it like this for this season and then redo the engine. Its got a MMW Polini head, 23t Serie Pro Clutch, PX200 Lusso gearing, I use a standard Si24/24E carb with a 128 main jet and a SitoPlus at the moment. Electric start flywheel with the ring removed.
I hope to use the same cylinder with a longstroke MecEur crank as I want a good reliable tourer with good torque for hills and overtaking - can anyone advise if the long stroke is the way to go ? Also if SiP carry a suitable packing plate 1.5mm . What effect will this change have on my jetting ? Any advice appreciated thanks,
Hello Steve, the longstroke crank only works well with a 1,5mm headgasket, a thicker basegasket makes the cylinder porttiming realy bad.
Importend is to center the head and gasket with a 1,5 headcompansasion. The piston tops the barrel with 1,5mm so the piston could touch the head if not centered correctly. I use two stud bushes art.nr 87105000 to correctly center the head on the barrel.
The longer stroke gives better torque butt the power shifts back in revs, this generale means a lower topspeed without a longer transmission
The Meceur crank has a shorter inletttime then the Mazzu and Pinasco, 165' open, it opens 110' BTDC and closing at 55' ATDC, this a safe timing for the risk of blowback.
The 24si is a real polini killer on long runs due to overheating a longer intake tract and bigger carb. Give better cooling. The jetting with a 60mm crank will sometimes be slightly larger. Very importend is to set the Si correctly, start with 50/120, Be3 150, an a correct main jet on color.
when i find it again i'll post you a link to a possible answer...
it says (or LaRocca says) that the long stroke crank will give more torque whilst the short stroke will give more revs in mid to high revs. (I do hope I got that right!) Im not sure how that affects you???
But I'm sure it was with reference to a similar engine to yours