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There is a vibration on my LI150 special that starts around 4000rpm and is gone just after 5000rpm. I have had the cranked checked and it's fine, fitted new silent blocks, crank bearings. Tried another flywheel, cylinder kit, changed the wheels without success. Any other suggestions?

Presuming that the crankshaft is as good as OEM (that is, not Indian with Lucky Bag big end) then the next suspect is probably the flywheel. Or even a slight misfire, especially with the plethora of badly made electronic kits fitted for, ahem, 'reliability' (Can you tell I'm not a fan? )

If you have swapped 'like for like' (as in an Indian flywheel for another) then the test may not be conclusive. "They're all made like that, Sir!"

The other thing that can catch us out is that sometimes, perhaps due to woodruff key height or other errors in manufacture, the flywheel is not always fully seated on the taper. I've had to fit other centres, concoct spacers & modify nuts, all kinds of tricks to get a good fit @ times. If a flywheel doesn't take a fair old bit of pulling (Oooer!) to remove, then it has to be made to 'fit'

Piston weight maybe
Change the headset internals for mb’s brass bits, works a treat on damping vibes

Warkton Tornado No.1 wrote:Presuming that the crankshaft is as good as OEM (that is, not Indian with Lucky Bag big end) then the next suspect is probably the flywheel. Or even a slight misfire, especially with the plethora of badly made electronic kits fitted for, ahem, 'reliability' (Can you tell I'm not a fan? )

If you have swapped 'like for like' (as in an Indian flywheel for another) then the test may not be conclusive. "They're all made like that, Sir!"

The other thing that can catch us out is that sometimes, perhaps due to woodruff key height or other errors in manufacture, the flywheel is not always fully seated on the taper. I've had to fit other centres, concoct spacers & modify nuts, all kinds of tricks to get a good fit @ times. If a flywheel doesn't take a fair old bit of pulling (Oooer!) to remove, then it has to be made to 'fit'

Sip crank and BGM flywheels.

ULC Soulagent wrote:Piston weight maybe
Change the headset internals for mb’s brass bits, works a treat on damping vibes

Tried standard cylinder and piston still the same. Would an head set vibration go through all the scooter?

Does this do it on the stand (neutral) and in all four gears ?

Just a thought, could it be wheel balance like in a car?

missing lynx wrote:Just a thought, could it be wheel balance like in a car?

Tried another pair of wheels.

The problem still sounds to me as though it is on the crankshaft axis. Even SIP & BGM can cock up & sometimes the woodruff key can be an interference fit on height. You can chase your own tail for ages on that I keep some that I have had to trim, step or even make from thicker material & step to remind me that we are in current day Lambretta World where quality is often only an option.

Is the front sprocket fully concentric, although clutch sprocket/clutch assemblies can run out of true?

Warkton Tornado No.1 wrote:The problem still sounds to me as though it is on the crankshaft axis. Even SIP & BGM can cock up & sometimes the woodruff key can be an interference fit on height. You can chase your own tail for ages on that I keep some that I have had to trim, step or even make from thicker material & step to remind me that we are in current day Lambretta World where quality is often only an option.

Is the front sprocket fully concentric, although clutch sprocket/clutch assemblies can run out of true?

The front sprocket is next thought, it has a 16 tooth one at the moment that is running a little out true because the chain tension varies. I will look for a Innocenti 15 tooth one, I did have one but cannot find it must have given to someone. The crankshaft was the first thing I changed without success.

Warkton Tornado No.1 wrote:The problem still sounds to me as though it is on the crankshaft axis. Even SIP & BGM can cock up & sometimes the woodruff key can be an interference fit on height. You can chase your own tail for ages on that I keep some that I have had to trim, step or even make from thicker material & step to remind me that we are in current day Lambretta World where quality is often only an option.

Is the front sprocket fully concentric, although clutch sprocket/clutch assemblies can run out of true?

If you are struggling, I must have a dozen or so 15 T sprockets (all Innocenti) of which I'm happy to send if it helps you eliminate it from your enquiries

Another option might be to remove the sprocket & chain & start up via the flywheel side (if you dare!) using a good drill & socket. Not an impact driver as that will just rattle the nut off. Another option, sometimes used on race machines, is to make a simple bayonet fitting. Using a flywheel puller would suffice & be even better than using the 17 mm AF LH flywheel nut, as both inner & outer threads are RH. With the puller fully inserted & the central screw locked in place with a nut, (usually M12) it would serve the same, temporary purpose.

It's not as mad as it might seem & I often strobe up an engine with the latter method prior to starting as a good benchmark setting, but I confess to never having started an engine in that manner, simply because of the load inflicted upon the crankshaft if all off the transmission is connected. It hadn't ought to be an issue with the chain off though.

I never thought of starting a scooter with a drill, I have done it with smaller engines like lawnmowers. I will try that later as I not much else to do. I will take your kind offer of a 15 tooth sprocket though, please, pm how much you want for it.

Tractorman wrote:I never thought of starting a scooter with a drill, I have done it with smaller engines like lawnmowers. I will try that later as I not much else to do. I will take your kind offer of a 15 tooth sprocket though, please, pm how much you want for it.

PM sent