PaulUsher

Thanks for the heads up. Remember filing an 8mm down literally decades ago! Wonder where it is now…

Thanks all. Looks like the head and barrel are coming off when I get the time, it'll not be for a month or so but I'll report back. Small end bearings are available from In Motion but it seems that OEM piston rings are all but impossible to find. So far have found a second oversize bottom (L-shaped) ring in the USA, and a couple of leads for specialist ring suppliers here in the UK. Fingers crossed!

1981 248 Montesa, same bottom end as 349. I’ve owned since new, got rebuilt about 15 years ago, done little since. It’s been a few years since I rode it and can’t remember if it always sounded like this but I think not. Any thoughts as to what this rattling is from those of you with better memories or bikes that do/don’t make this noise? Thanks. Video of bike running: https://drive.google.com/file/d/1hDHj3LvyNAvQO7q4dQYDrzyU5u1NtZ_K/view?usp=sharing