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The standard data sheets show a maximum regrind allowance of +0.040".
However I see +0.060" shells are also available for both main journals and crank pins-any advice/experience/update on going this extra 0.020" would be good?
Thanks in advance

I don’t know myself Howard, however a few years ago I had to have a non Triumph engine reconditioned and I’d recommend the guys at Middlesex Reboring in Lawrence Street, Mill Hill NW7 for their knowledge if they are still there.

Might be worth a call.

Adam

Be ok for normal road use but we were always told to avoid too deep a re-grind because it obviously weakens the crank and you will loose the surface hardening unless you get it redone.

The correct answer really depends on the use you intend for the engine. As stated above, ok for lower stress road use.
However there was a practice several years ago to offset grind the big end journals to the maximum thereby increasing the stroke of the crank & the cc's of the engine. This was often accompanied by polishing, shot peening, tuftriding then balancing the whole rotating assembly from clutch through to crank pulley. Also balanced rods & pistons. This theoretically smoothed out the engine & improve reliability at higher revs.
So if expense is not an issue, go for it, otherwise stick to minimum necessary regrind to provide a reliable standard engine.

Thanks for all the input. I hope to avoid the +0.060 if/when the time arrives -cheers

Carefull with the hardening, it is rather thin