Can I bore out to 72mm?

[phil23fair]

I've got an iron linered TS1 that is bored out to 71mm. I have just ordered a new set of piston rings for it, but the piston to bore clearance is 4 thou. I know that is the normal clearance if it were a cast barrel but is it excessive for an iron linered barrel? If it is could I safely bore it out to 72mm and use an RB250 piston? The iron liner spigot thickness is 2.3mm, so that would come down to 1.8mm.

[dscscotty]

4 thou is fine on linered cylinders, 72mm is possible but you will have a very thin and weak spigot that can break.

[carlos fandango]

Thats what im doing at the moment, iron lined Rb 71mm bore and worn out .
There are no 71mm oversize pistons , so ive looked at M/C pistons YZ , H2 etc which have 71+mm pistons, but this lead to changing my rod and head , so im going AF 72mm wossner
Im a little concerned about the thickness of the spigot ? .........but, when i had it lined originally they bored it off centre resulting in the one half of the spigot being 1.5mm thick and the other half 2.5mm
So ive ask for it to be centralized ie taking more off the 2.5 mm side which should leave 1.5mm (ish) each side. Its been fine with the one side at 1.5mm so i see no reason why when both are 1.5mm it will be any difference. I think a factor to take in to account, is how snug the fit of the spigot in the casing is , if its a really sloppy fit then it will be under more stress ?

[Wack]

Bore the casing and fit a thicker liner?

[phil23fair]

Thanks for the replies. I shall refit my 71mm piston with new rings and when the piston to bore clearance gets too much go down the 72mm route.