mark wrote:could you please explain what this modification will do
?
Ha ha....good question!!
But to save a lot of debate....i'll refer you to a previous post:
http://scooterotica.org/forum/viewtopic.php?f=7&t=40
And here is an excerpt from said post........
OK, so.......what the f@@k are we doing machining down Lambretta cranks??
Well, its fair to say that this is a liitle experimental from our end, well at least on Lambos anyway, Sean has done a lot of these cranks on Vespas, and they prove to be a great success. Of course, the induction system on a Vespa is different to a Lambretta, but there's a lot more to this than just the inducton.
So, what are we hoping to achieve? Well a few things really, non of which are MAJOR big deals, but all add up, and along with the rest of thE engine mods, make for a more efficient and powerful engine. So we should see.....
1) A decrease in rotating mass.......ever seen BHP increase when a lightened flywheel is fitted? Same principle.
2) The crankcase volume does come into play on a Lambretta, slightly differently to a Vespa, but the gasses will flow in a smoother fashion (especially in conjunction with point 3).
3) The version we are doing for the racer will have the crank case metal removed to lower primary compresion, the reduction of material on the crank will further assist lowering the PC also.....especially as the 'full race' version will be more of a 'bell' shape than a circle.
4) Increased lubrication to the crank big end.....which on an RB kit (which is what we'll be using it on) is a useful thing!
So.....decrease in rotating mass, improved gas flow, lower primary compresion, increased lubrication. Add these items to all the other minute changes we make (a finger boost port direct from the inlet tract to the casings, etc etc), and the race engine should be a sweet little number
