I refitted the dep pipe on my A.R. tonight, had a look through the exhaust port to check the condition of the piston. The piston wall looked very smooth, but just below the ring there is a very light brown discolouration, is this a problem. Worried,. Berkshire.

Kev, whilst it's not an ideal sight, IMO,you don't have to worry to much
I would do a compression test, and if it struggles up over 140 psi, don't worry this year, and have a top end strip come the winter, new , rings, T/E, bearing , gudgeon pin etc
Mike

Not a problem. If dark brown/black then you have worn rings/piston as gases are blowing past.

Thanks lads, I,m off to read up on compression testing now. What would be a good reading for compression.

You can buy them at Halfords ,etc, the easiest way to do the job, is to take off the tank, and loosen the rad shrouds to push them forward out your way.
This gives more room to manoeuvre, and more importantly, less chance of cross threading the tool in the otherwise tight area above the cylinder head.
Screw, in the tool, half a dozen good prods on kick start, check reading, release pressure, repeat a few times, and take the average of the readings, BYUFYA, job done.
Mike