850 pistons ID

G Day All,

Have just stripped the top end of my 850 MK3 and was wondering about how to tell what size the pistons are- you know STD, 0.20, 0.40 etc. The only marks I can see stamped on the crowns are 'B'. Does that denote STD? Forgive a novice but I don't have the equipment or knowledge about how to accuratley measure the oversize- but in my experience oversize pistons usually have the oversize 'size' stamped on them- 0.20, 0.40 etc.

Am I missing something before I order new rings? I should add the old wheezer has 28,000 miles on the clock and generally performs like a new- ish 36 year old Norton(!) - smooth, mechanically quiet but just getting abit smokey when shown the whip!

Many thanks,

crusadersports

If its been oversized, Hepolite pistons will have 0.020 stamped on the crown. Just carefully scrape off any carbon around the centre of the crown and the marking should appear. if there is no such marking, it will be on standard bore size. As the barrel has to come off, you may as well do it now and measure the piston diameter and the cylinder bore to verify the actual piston size. Re-ringing is not always the best solution depending on the actual wear.

Mick