dans new crank

[sean brady scooters]

dans new fully modified crank for RB20..........took me ages to do..........









approx weight of a std crank...............2114 grams
..........this one now...........................1810 grams......so 304 grams lighter

[mark]

could you please explain what this modification will do ?

[Avantone]

If it works as good as it looks..........

What are you expecting Sean? Dyno before/after?

[drunkmunkey6969]

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

[drunkmunkey6969]

What are you expecting Sean? Dyno before/after?

Not the world......but sufficient to make it worthwhile.

We already know from other milder versions Sean has done, running on other Lambrettas, that this type of mod actually makes for a smoother engine, with snappier throttle response and extra revs at top end. One chap had a longstroke crank that was "making the scooter rock forward on the centre stand at tickover".....this mod gave him an extra 500 rpm at top end, smooth tickover (no rock) and a snappier throttle response......so we shall see.

I have some more info re dyno results......but i have to wait until ive got all the 'bits n pieces' together.

[davidblythe]

Always did wonder why noone seemed to have tried it on a Lambretta, it was a common mod to knife edge cranks on Cars

[drunkmunkey6969]

SX150 casings...i've fitted the Li150 gearbox, got it all shimmed up, race bearings & rolf seals fitted, i then took a standard innocenti crownwheel and trimmed it to accept 5-plates (6 with FOXHAT spider) and drilled to lighten, casing mouth shown as standard still...but Sean will port to match RB20 soon. When thats done i'll get rest of build finished and check port timings before whipping cylinder off for Sean to continue working some magic with the old die grinder!!!

With this spec and Seans porting to cylinder, casings and crank.....it should be lethal!!

[joespeed]

well it does look good,keep us informed of how it performs,
regards
joe

[camel]

hope your fillings are secure!! ..interesting stuff,keep us posted

[Bufficus]

What bike is it going into Dan?