Imola Piston Failure

[nellyboyo]

Had this happen on my imola the other day. Still just about made it home revving the tits out of it , but no idea what caused it as it had been running great. Been replaced now with a Race tour .
Its a version 3 imola. PWK 28mm, and scootrs pipe , was running a bit rich and doing regular plug checks. It looks a bit lean I think form the me ring it home part .
Anybody any ideas ....or just S@@t happens.
Its cracked all the way around under the gudgeon pin.

[nellyboyo]

Well it was a 2nd hand standard Imola 186 kit that all looked all right to me.
I didn`t think that nicasil can wear non-uniformly up the bore , if you know what I mean .

[Adam_Winstone]

You're right though that the crown colour indicates that it was running very weak at whatever throttle position it was at when it went bang! When you put the new piston in then you may want to review your jetting (and possibly timing and/or plug choice) so that it doesn't do nasty things again.

Do Imolas come with these pistons as standard? The piston does look like a standard Asso item with 2 holes cut in the skirt, which would not have the additional reinforcement aroung the holes to avoid cranking and skirt failure. You can also see that it shows the standard piston/Asso tight corners where the skirt meets the gudgeon pin bosses, which is another common failure point and has been addressed on any decent piston that is now supplied in a modern Lambretta kit.

The MB pistons do have a much more modern design and big radii transfer windows so you shouldn't suffer this fate again, unless bore clearance is way too big.

Best of luck.

Adam

[nellyboyo]

OK tidy, my spelling was bad in my initial post ,
I`m quite sure...( famous last words ) ...that the weak look was from me riding it the 10 miles home with half a piston. I had been really paranoid and checking it regularly.
I looked inside the piston and there is only 1994 marked in the skirt , so this may mean that it wasn't a "proper " imola piston anyway . .
Anyway the MB one is in and it really is a quality item . It must weigh at least a 3rd lighter than the one that came out . I`ll take my time for a bit ..100 miles ish , before I really start giving it some.