Hi Mike.
I have a 3.5, 6, 8/1 bitsa
The 'plate says it started life in the early '30's as a 3.5/1 hopper cooled, when it got to me it had a 6/1 top end.
Someone had poured sand in the crank case, honest!, and then it had been topped up with grease, I pulled it completely to pieces and boiled the crankcase and sundry bits in a 40 gallon barrel with a couple of kilos of caustic soda and started again.
The mains and big end were wrecked, so, having had the big end reground to suit a hugely undersized Rajkot bearing I eventually I fitted taper roller bearings, with plenty of Loctite (620, I think).
It was massively out of balance (I did the Butch bucket and string test but can't remember the details, they're on one of my previous posts, I think) so I sent off for a Rajkot 8/1 Aluminium piston. With no other counter weights it runs like a Swiss clock, well nearly!
There's a massive difference in weight between the iron and the allu pistons, again I can't remember how much, 25%?, maybe I should document more.......
Here's a link I've posted before, of it pulling 2.3 KVA
https://www.youtube.com/watch?v=js3zz6CECqYIt starts to get excitable around 675 rpm, so hopefully, when it goes into off grid duty, at around 625 rpm, in the next couple of years or so, it'll be fairly long lived.
Cheers Stef