Scooterotica

with all the current debates going on regarding cranks..........
i thought i would just put this up to see what you all think...............

a mate of mine..Niel bought a std li 150 about 6 years ago..........and asked me to rebuild his motor and to also tune it..........

it had done approx 15000 miles...........
i then gave it a stage 4 tune..........still on 150........std piston......but with 30mm delly/fresco pipe.............
on inspection his crank was still spot on......which quite surprised me...........so it was refitted................and so for the next 2/3 years he blasted about on this ............
he then wanted more power/speed..........so we fitted a tuned AF 175 kit.........sterling pipe
........which he has run now for the last couple of years...........
its fast and reliable............75mph tops maybe..........
but the point is ..............its still on the original crank that has done now in excess of 25000 miles.......................
this may well be strange and unusual...................but is true

I wouldn't say unusual.

We can tend to be "blinded" by the fashion to replace every component in an engine. More often than not, it appears, the replacement parts aren't up to the quality of the original parts.

If it ain't broke, why fix it?

Chris

apart from the taper size whats the differance between the gp and li crank?

Back around 1970 when I was in my first flush of scootering, sheared woodruff keys and mangled tapers were the biggest problems. Mind you, we didn't posses sockets sets back then let alone exotic things like torque wrenches

I also had the standard crank on my TV200 twist and a friends Royspeed tuned SX sheared it's crank. Apart from that and concidering a lot in our club were into grass track racing crank problems were fairly rare.

My 1964 LI 150 engine with a Muggy 186 engine still uses the origiinal LI crank. The muggy kit has been on since 05 though not constantly ridden.

My Saxelby 185 motor ran a thin taper crank for god knows how many thousand miles and would rev its tits off! So not realy that unusual.Made sure the flywheel was light though.And only used semi synthetic.

A smaller taper should only suffer through Inertia when using a heavy flywheel deceleration and acceleration forces. The rods are not the strongest but a similar crank was pretty reliable in an SX200 or the Servetta... Some on the track are running very quick motors using SX/LI webs but with a decent rod kit fitted and a light rotor for the ignition....

But I have ported Three engines that have used these cranks that broke... The taper of the crank broke at the mag Bearing shoulder..

There are some massive forces indeed happening around the crank and the crank pin especially, if the pressure fit of the pin is only marginally out there may be trouble.
I found this of particular interest it’s not really relevant to a scoot but the principles are the same, beats punching the numbers into a calculator any day.

http://www.mscsoftware.com/support/libr ... stress.pdf