The end of the Lambretta crank as we know it ???

[Avantone]

no mate...............
if bottom end grunt as you call it was worse................how then would such motors accelerate..............
the pins are tighter ........just to accomodate the extra power ...................derived from these..................

Not sure I agree Sean, but what do I know...................... had too much red meat today as you'll see from my posts .................... think I should retire.

[drunkmunkey6969]

........can we assume it doesn't lend its self to bottom end grunt and 4-speed boxes?

I dunno, its hard to say....i wouldn't like to commit either way.......but i guess Steve Conneely will be running whatever Charlie runs...and Steves scoot is whacking out 35bhp peak power, and the peak torque of 21ft-lbs is only at 7800rpm. Thats a high-level race tune...so is it inconceivable that the same crank could be used to make a torque tuned motor??

[tony]

Sean I do know the figures but I really dont want to say if thats ok.
Re steve's motor..That is what Charlie terms a customer engine as it says in the article. There are a few out there in group 4.

[tony]

in a HPC ratio motor.......much of the inertia from the inlet charge is cancelled out because of the higher pressure in crank /flask area.................

where as ,a lower primary comp ratio will let more charge in,and also has more space inside to accomodate it.............
a lower PCR therefore allows an engine to not only rev higher and more freely(due to less pumping pressures).........but inhances the effects of tuned intake pulses and ex pulses to the max effect....................

So it's good for extra power at high RPM? i.e racing?

As the exponents have been CE, Stuart/SRP and MX in general, can we assume it doesn't lend its self to bottom end grunt and 4-speed boxes?

Reading between the lines on MB's quote regarding "problems", is balance an issue with it shaking out of balance on the big end? (hence the mention of "tighter")

How big is Charlie? he's pretty tall and must weigh a fair bit. So to get that thing of his to pull he needs big torque.

Sean, i see the pins take ten tonne to press. Here's a test when it comes around. After running the motor for some time see what pressure it will need to press it apart and back together. Be interesting to see it it stands up to the abuse we all give our motors.

[Special X]

Surely the PCR of a 200cc lammie case is too high. The crankcase volume was designed with 125/150cc in mind and then 175cc made it too high and the 200 even higher due to the increased swept volume. IMHO (having tried the HPC route with spectacular lack of success) losing 40cc on a 225 motor would still leave the primary compression on the high side allowing for copious porting of the transfers while maintaing a decent primary compression. I think the crank will work well.

Let's see some graphs

[Special X]

Tony . . I believe MEC flywheels take about 10 tons to press and they tend to stay straight, unlike a very popular race crank that takes about 3/4 tons if it's a tight one

[Avantone]

Surely the PCR of a 200cc lammie case is too high. The crankcase volume was designed with 125/150cc in mind and then 175cc made it too high and the 200 even higher due to the increased swept volume. IMHO (having tried the HPC route with spectacular lack of success) losing 40cc on a 225 motor would still leave the primary compression on the high side allowing for copious porting of the transfers while maintaing a decent primary compression. I think the crank will work well.

Let's see some graphs

Yeah - who do we know with a crank, a Gp.6 scooter and a dyno?

Come on Dan, the floor is yours...................

[drunkmunkey6969]

Going back to the infamous CE article, if you read between the lines you can pick out the info...first he refers to Gerry Pell (top LC tuner) that does work on his cranks.

Then in his tuning philosophy he refers to the combination of crankcase pressures, in combinatin with big pipes and madder porting etc. He next refers to packing the crankshaft as being 'old mans route' and the 'wrong way' . He outlines a standard Lambo with box pipe as being 1.65:1 and a modern motoX machine as being 1.2:1.....and the fact that on a Lambretta that runs a decent pipe, you actually need to increase the volume in the crankcase. He again goes on to repeat his statement yet again, that low crankcase compression is one of the keys to making good power, and that you have to have the right pipe to work with it.

Finally, in the section at the end called 'inside the beast' his crank spec is listed as: Modified Tino 'supercrank' webs, fitted with a long Japanese conrod and welded pin.

So you tell me......if HPC and crank stuffers are old mans route and the wrong way, and he repeatedly refers to crankcase pressure and crankcase volume as being key to making good power, he has top LC tuner Gerry Pell re-working his cranks, to use a long rod (presumably this a lower comp height piston with packer plate) and his crank webs are 'modified'.......am i completely mad to be thinking that Charlie is running an LPC crank similar to ours and similar to MBs??

Mark Broadhurst was using these types of cranks back in 1990, and the scooter it was in is still running! Sean Brady has been doing them for a similar period in Vespas, and has more recently (amid much negative speculation ) being turning them out for Lambos.

Now Mark comments the following:

OK, I asked Paul Baker what cranks they were using in Stuarts bike, they said a low primary one, I ask if he had problems and the upshot was I said I would see if we could make a balanced, tighter LPC crankshaft for them to test. SRP Racetec run an LPC crank too, and I built the one in the thread before I set off on the Euro. Interestingly, I spoke to a tuner who said they get 3-4 bhp more on a RB with a LPC crank! They can not get the power from an RB without lowering the primary compression!

So........we dont have the graphs to show you back to back....but the evidence is there for all to read, and interpret as they wish. Nobody except Charlie and a select few friends knows exactly whats in his crank case.....maybe he's scooping metal out inside there somewhere and its not off the crank, or maybe it is off the crank but in a different way....who knows....but those that want good power in either fast road or ractrack applications might find that little something they are looking for, in something like this by MBD:



or this by Sean Brady:

[drunkmunkey6969]

Yeah - who do we know with a crank, a Gp.6 scooter and a dyno?

Come on Dan, the floor is yours...................

I can feel myself caving into peer pressure!

I may have to bring forward the timetable for fitting the LPC crank to the racer....i just need to get a 70mm reed-piston from Mr Broadhurst with a 30mm comp height first.

[Avantone]

So you tell me......if HPC and crank stuffers are old mans route and the wrong way, and he repeatedly refers to crankcase pressure and crankcase volume as being key to making good power, he has top LC tuner Gerry Pell re-working his cranks, to use a long rod (presumably this a lower comp height piston with packer plate) and his crank webs are 'modified'.......am i completely mad to be thinking that Charlie is running an LPC crank similar to ours and similar to MBs??

Maybe ................. but as Blackadder might say "They're as cunning as a fox what used to be Professor of Cunning at Oxford University but has moved on and is now working for the U.N. at the High Commission of International Cunning" .................. you never know!