Scooterotica

well after another piston and rings 150 miles later same thing happens again
looks like the rings are snagging on the exhaust port,was going to pick my lad up
after work,lost power at 50mph revs climbed grabbed clutch leaver and rang a very nice man
to pick up..

What is the engine specification? Carb, pipe, airbox or open etc? The exhaust does not look wide enough to be a problem but the condition of the bore does not look great. By this I am not talking about the seize mark, I am talking about the lack of a cross hatch hone marks. Has this barrel been properly honed true? What is the history of the barrel?

The exhaust port looks like it's the right shape but it does look like there's some 'squaring' at the top of the port consistent with the rings snagging. Is it possible that the rings got stuck in their grooves due to an earlier seizure thus not allowing the rings to fully spring back? Just thinking aloud

at mo running a stage 4 top end,rd rod,2.5mm packer,expansion pipe,30mm delly through panel,sean tuned just under 15bhp, this barrel has done approx 1700miles,1st time summit happened was crap base gasket some people reported on here,hone 1,then the next time piston ring pin came out and snagged the exhaust port thats what the nics are on the photo,hone 2 and now this has happend
and yes the piston is in the right way i ride in all weathers to and from work but this is getting me down.

Ta too all who replied, Paul

oh dear tosh ,you dont seem to be having much luck with that ..thought you also had a fuel starvation prob ...as well as the base gasket failure ...did you get that sorted .
so who did hone 1 and hone 2 and the rebuilds ?...only asking cos it wasnt me

Hi sean how r u

a gent who restores classic nortons across from our works did the hones 1/2, yes i sorted the fuel prob out it was the plastic handle on the metal arm that was spinning on it and thus not turning the arm far enough
to turn the tap fully.i did the rebuilds checking the piston clearance/ring gap was right then the squish 1.2
there were no leaks from any gaskets or the head and i wouldn`t put the blame on anyone its just my luck

crank out of line ? as a lad in our club had problems eating rings and he ended up haveing to but a new crank in (sil 200)

To be honest I'd check the hone, It should have a cross hatch pattern in it even after 1700 miles. Secondly, and this is by far more probable, see if you can check the concentricity of the bore to the base gasket.

I got given a cylinder to sort out once. On inspection the bore was not square to the cylinder so the piston would have greatly reduced clearances top and bottom. The clue was looking at the chamfer on the skirt of the barrel, it was not even around its circumference. Worth a look I think, but I'd get that bore checked at several points for ovality up and down the bore.

given that there is a definite line to the seize marks in first pic i think rich is correct