Piston woes....

[Timbo]

Running in a 68 Racetour piston in a rebored barrel. Piston and barrel were matched. Done about 450 miles and was riding back from Coventry 45/48 mph max. Was on a dual carriage way when I lost power and engine cut out. I knew I had lost compression from the kick start and guessed it was probably the rings and sure enough the bottom of the rings appear "welded" in Barrel look ok ish. Plug colour is ok. Any thoughts why this has happened? Is the very expensive piston recoverable? Please be gentle...

[RobD]

Speed you were doing is to a certain extent irrelevant. Were you varying throttle opening / speed or sitting at a constant speed? Coasting downhill on a partially open throttle? Did you have a full tank or near reserve? What carb and what float valve?

[Timbo]

Yes varying throttle, and had filled up 15/20 miles earlier (crap petrol?) Using mineral oil which I poured on top of the petrol. Would it have mixed? Was doing a constant speed for 5-10 miles as was on dual carriage way. Not coasting and didn't go over half/two thirds throttle. Newish 26 delly.

[tea5ive]

whats in the carb jet/slide wise ?

[Timbo]

108 main, needle is 2nd notch. Can't remember the rest but can look. Is the piston completely fecked?

[rondord]

s**t piston
s**t oil
s**t petrol



all of the above conbined result in pistons loiking like that

[cgt75b]

Oh Timbo just when u were taking the p155 out of me with my problems my advice is buy a new scooter it's knackered

[Grumpy225]

s**t piston
s**t oil
s**t petrol



all of the above conbined result in pistons loiking like that

That's an RT piston, wouldn't consider them s**t by any means. I beat the hell out of mine and 3k miles later the motor still fires first kick.


This is the problem "15-20 miles after a fill up while using mineral oil that was poured in after....."


User error.

Your piston is a door stop now.

[Timbo]

I put in 4.8 litres into a 11.5 litre tank so would have thought it would have mixed ok...

[speedy]

The oil will mix as it's heavier and will sink and vibration will mix it in. I don't like mineral oil nowadays in any scoot, especially not converted cylinder/performance engine to be honest,but you've been running it in the bike prior to this I presume, so it's unlikely to be oil,especially as you weren't wanging it. There are no air leaks on the cylinder are there?