Hi Bob,
It took me so long to unndo the bolts then carefully remove the cover peeping inside to see if anything was under tension and fly out at me. Fortunatley it is a simple cover and the pump and cam yiming are untouched, That large spring for the pump was easier than expected to remove or maybe I have done too many brake shoes on drum brakes over the years.
At the moment ignore thos numbers I posted. My new chinesium internal gauges told lies.What was happening is I would compress the ends and lock them in place. Then unlock them and let them fly out and then I would start to lock them remove it and take the measurement. It was not until today that I read those numbers again after having so much crap run around in whats left of my ageing grey matter. I discovered the tighter I did them up they would pull the ends in hence giving me those numbers. With more patience and time I will get new numbers and todays numbers show 0.003-0,004" wear in the bore at mid and near where the top of the piston rings would sit at the bottom of the stroke. Of course TDC n BDC read STD 4.5" which answers your question of STD size.
This is a CDM model meaning 'marine' model which run dry sump and wet sump depending on application. Now Lister used the marine model for boats and gen sets and this one being the high speed model would almost have to of been made as a genset from new and that was its job at the farm it came from.
The big end bearing is not on the website as a spare but I sent Rob an email today asking for a STD ring set, full gasket set and if he had a big end bearing. I am not concerned about the big end bearing really but asked just incase. I fully intend to put the piston in the lathe and tidy it up and make it respectable. I had to machine the skirt of the piston in the McDonald Super Imperial Diesel I brought back from the dead and after all the neigh sayers telling me you cannot and should not machine a piston and never the skirt I went ahead and did it with great success. After posting the pics of it in the lathe and what I had to fix then a video of it running it was funny as there were no more saying you cant do that. So this one will be tidied up and new rings and thrown back in.
I am guessing as I do not have much info on this engine only they told me where and what it did on a farm so previous history is a total guess. I have a lot of cleaning up to do and might make a start on that tomorrow but need to do some work around the yard and drag a goat out n cut grass, just dont know which goat yet.
Thanks for your onging interest and ideas.