con rod bearing big end scored

Well not ideal but it rather depends on the condition of the crank journal, if the crank has severe scoring on it matters will only get worse - rapidly.

If however the crank journal is ok then possibly the con rod bearing will be ok to use again, you will need to carefully clean off any burring along the lines of the scoring and thoroughly clean the internal surfaces of the crankcase and the sump to remove any contamination that was possibly the initial cause of the scoring.

Thanks Hillsider

Crank is looks fine - I will follow your advice.

What is the best method of de - burring the score lines on the bearing?

Do you use very fine wet and dry paper and a wooden dowel as it seems to be light alloy?

The sump and engine block have been thoroughly cleaned.

I think that unless anyone has a better idea I would go along with your suggestion of using very fine wet and dry paper. You certainly don't want to use an emery cloth that can leave abrasive particles behind, just be careful to clean the surface thoroughly and hopefully you will get some more life out of the engine.

I should point out though that although you have said that you cannot feel any slack in the bearing there could well be enough wear in it to allow it to rattle a bit when running, only time will tell on that score (no pun intended).

I wouldn't worry to much about those scores or do anything to them . If you've cleaned all the muck and grit from the sump I' d just fill up with SAE30 and start her up. The cast iron Suffolk engine which has Briggs and Stratton ancestry is low powered and low stressed and unlikely to be too bothered by a score or two. Hillsider is is quite right in advising against emery paper but I would go further and say don't  even bother with the wet or dry, but do give the bearing a good squirt of clean oil on assembly so that it doesn't start up dry.