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I have just taken delivery of a 71mm Wossner piston modified for a TS1. The TS1 barrel is iron lined. The piston box states the piston is 70.96mm diameter and clearance 0.05mm which is 1.97thou. I seem to remember reading somewhere that for iron lined barrels clearances should be closer to 3.5 thou. I’m taking the barrel to be rebored at the weekend so any advice is gratefully received.
Also what sort of running in regime should I follow with an iron lined barrel?

follow the clearances in sticky's & Lambretta maintenance manuals
its an iron bore so first full tank of Castrol mineral 2T, then back to semi / full synth.
I'm old skool , I run all rings in @250, pistons @500 & new kits / re-bores @ 1000 miles.

From MB's site

Alloy cylinders .0015 - .002"
Alloy with cast iron cylinders .002 - .0025"
Cast cylinders .003 - .004"

My logic thinks that the result of an iron sleeve in an alloy cylinder is very similar to a Rapido in which case anything less than 0.003" is likely to be tight. The Rapido's were notorious for being tight & on a 70 mm bore, I found it necessary to cross hatch hone to 0.0035" with cast (Suzuki) pistons. The Wossner pistons are probably similar to Wiseco in being forged, so perhaps 0.003" would be the target....

Thank you all for your replies