bsa mercury piston head

[dalesman917]

I have just stripped down an old Mercury Mk1 that wouldn't cock and found exactly as this thread describes. Piston was jammed in cylinder and 'scraper ring' on nylon head hopefully the cause. It was also fitted with a nasty square section mainspring but that's another story. Intend fitting the steel export head and reverting back to standard spring and we'll as adding tune kit with improved spring guide.

Just wondered if anyone else has fitted the export head and was it worth it?

Great thread, searched high and low and found no reference/mention of 'extra' circlip ring until here's . Looks like at least part of the old girl remained unmolested then. Funny how it took over 40 years to cause a familiar problem...