So,what caused this then??

[kevspeed]

Bog standard GP150,no air leaks,jetted correctly,running fine (well,for the past 6 months anyway)
Luckily only travelling at 35-40 when it happened!!

[Mr G in NYC]

F++K me thats nasty....cranks snapped nasty ...piston seized and twisted and snapped
the crank.... did you forget to mix oil in the petrol ? or changed down from 4th
to first at 50 mph by mistake ? G

[kevspeed]

F++K me thats nasty....cranks snapped nasty ...piston seized and twisted and snapped
the crank.... did you forget to mix oil in the petrol ? or changed down from 4th
to first at 50 mph by mistake ? G

Not me (fortunately),one of the local feller's,luckily no one hurt,except the wallet!

[Mr G in NYC]

Phew....... thank god he didn't come off like .........G

[rosscla]

Ouch, looks like a twisting type break rather than a straight fatigue, hard to see in the pictures but is there shims in the crank or on the piston? Does the small end still move?

If it's an original crank it could just be age.

[Yanker]

SIL rod failure due to excessive piston to bore clearance (evidence the blow-by), Ring failure (where is the top one). Small-end bg failure: check as suggested by roscalla. Pics are poor: check big-end and main bearings. Coupled with poor quality components?

[carlos fandango]

Bad fuel ? ......lol

[scooterslag]

Bog standard GP150,no air leaks,jetted correctly,running fine (well,for the past 6 months anyway)
Luckily only travelling at 35-40 when it happened!!

Nasty as f@@k be interested to see what you can find out about this

[dave411]

Seen this on two stroke outboards.Normally so much damage it hard to diagnose,but we think it's a piston seizeure caused by detonation,never lack of oil or over heating,as the engine still runs ok,but only on five cylinders.

[kevspeed]

SIL rod failure due to excessive piston to bore clearance (evidence the blow-by), Ring failure (where is the top one). Small-end bg failure: check as suggested by roscalla. Pics are poor: check big-end and main bearings. Coupled with poor quality components?

Top ring is present,small end is still free,mains are good,mostly suprised at the chunk of barrel spigot thats smashed off,and the fact that the engine casing isnt damaged!
Original 1979 Indian 150cc motor,no modifications except for a 12v electronic,as the lights on the original points set up were dire!,pity as was running faultlessly,still,its Lambretta isnt it!