Dropped piston ring

[ricardo59]

Just been informed by my mechanic that my scooter died due to a dropped piston ring, anybody any ideas why it would do that?

[bristolmod]

1) cylinder way over-bored
2) ring peg lost allowing ring to spin in its groove
3) ports not chamfered
4) exhaust port too wide for diameter of cylinder
5) simple failure of ring- worn/ damaged?
6) sods law......

[garry inglis]

you have to tell us what kit was this on

[holty]

maybe a few pics of the piston and barrel might help to work out what went wrong ?

[ricardo59]

Polini 177 kit not matched or ported, PM exhaust and at the time a Delorto 30mm carb ( now running a Delorto 24/24 ) was using 2% mix now using 3%
Don't know how to put pics on here?

[wrecklessrobbie]

On your other thread i advised you check the basics cdi,ht lead etc and piston and rings.
which you have done.
I suspect the carb was not set up correctly. However i am no expert.
on my li 175 ally af barell i had the same problem.
i know its a different scooter.
it turned out the carb was jetted incorectly. Causeing a mild seize that snapped the lower piston ring.
Af managed to sort the asso piston and fit new rings.
the barrell was only lightly marked due to being steel so i was able to emery it down.
they rejetted the carb.
i run 3 to 4 % mixture. Bit rich which can cause problems. But 5 years on it hasnt been a problem.
Hopefully you will get better results with the new carb.

Robbie

[ricardo59]

Thanks for the info...it seems i had the same problem but didn't catch it early enough! hence all the damage! wether it was carb not set up right or wrong mixture who knows?

[wrecklessrobbie]

To be honest im not clued up enough on carburation to know.
its just what af told me.
many years ago i tried a 30mm dellorto on a vespa. It ran like a bag of poo. Took it off and it was better. But i dont really understand jetting and mixtures back then. Still dont. I know what it should be....but achieving it is beyond me. So i get my scooters set up or dynoed.
Personally i think its the hardest part in scooter building.
You can put on any cylinder, exhaust, gears and carb. But if the carbs wrong it wont last long.
i personally like iron cylinders for me easier to sort if they go wrong. Others prefer nicasil lined. Just personal preference i suppose.

Robbie

[ricardo59]

Me and you both, i don't know much either thats why i bought this from a shop that deals with scooters thinking it would be set up right, think i might send them the bill ( £486 ) and see if they will go halves with me.