Lambretta LD flywheel restoration

[Bettagetabrettabolti]

Chaps
Has anybody rebuilt the automatic advance built into the ld flywheel. The pins seem loose on mine.
Any hints tips or guidance would be appreciated.
Thanks
Bolti

[jbcollier]

Warning, personal rant mode engaged:

Really? You want the timing to ADVANCE as the engine picks up revs?!!

They really didn't have a clue about 2T porting, combustion character and ignition timing back then. You should see some of the whacky designs they came up with: deflector pistons, double pistons, etc. Dump the advance.

Rant mode off.

[Bettagetabrettabolti]

So JB would you suggest the variatronic conversion? Did want to keep it standard but appreciate this is the 21st century and things have moved on.
Cheers
Bolti

[jbcollier]

No need to fit a turbo and an intercooler, just disable the advance and run fixed timing.

BTW, nothing against the varitronic, I run one in mine along with a bunch of other mods.

[Steve J]

Whoa - take it easy! The auto advance on the D/LD models is nothing more than a device to RETARD the ignition for starting, in an attempt to prevent it 'kicking back' when trying to kickstart it. The device was designed to provide the spark at around 8 degrees BTDC for starting, rapidly advancing the ignition timing by 18 degrees to the normal running timing of 26 degrees BTDC by the time the engine had reached around 1800 rpm - equivalent to around 18mph in top gear. Ever tried riding a D/LD below that speed in top? FWIW, early D/LD machines did not have that mechanism, and were set to 26 degrees BTDC static for the 150, and 28 degrees for the 125. And before anyone claims those advance figures are excessive compared to later Lambretta engines, remember that the LD engines had a lowly compression ratio of 6.5:1, a hemispherical head with no squish, and the mixture burnt more slowly - hence the requirement to start the bonfire sooner!

The varitronic ignitions are designed for higher revving engines, giving full advance at starting, and retarding the ignition for safety at high revs, especially above 6000 rpm. As this is above the operating range of (unmodified) D/LD engines, I question the usefulness of the varitronic on these engines, other than to get rid of the contact breaker. A system based on the GP type electronic system would probably be all that's needed, but watch the weight of the GP flywheel on an engine with such a narrow crank taper.

Bolti - if you do decide to keep the 12 volt LD flywheel, be aware that the flywheel cam on the AVV engines is different from the cam on the usual 6 volt magneto setup. As the 12 volt system uses a conventional coil and battery setup, the cam is designed to keep the points open for most of the flywheel rotation to reduce the average current drawn through the ignition coil. Fit the wrong cam, and the battery will probably go flat even sooner, and there's a good chance the coil will overheat and fail.

[jbcollier]

Yup, no squish, hardly any compression, a crude carb and an exhaust designed like a small suitcase. There's a reason you never see D/LDs popping wheelies. Also agree there's nothing wrong with the timing spec. Just lose the advance. It's a needless complication.

[Steve J]

There's at least two more reasons why you won't see a D/LD pulling a wheelie - one is the rear axle, the other is the torsion driveshaft. One or other of those will fracture if you try it! Assuming of course, the crankshaft doesn't break at the flywheel taper first.....

[Big Al]

It sounds as if a better name for this device would have been an "automatic retard and revert mechanism", if the retarding comes first, before the reversion to the normal running timing.
Maybe something was lost in translation.