Stan,
Years back, they scraped everything. Modern bearings are made to tight tolerance. Should be no need to scrape. Scraping is good for around 80+% contact area. I have no bothers with scraping bearings. There is enough metal on these bearings. I have no idea if mine was -10 when it started. I have a -20 set and would not worry if I needed to machine it for a standard crank. You worry too much. These engines were built long before the throw away age. Yes the modern day 'Lister' owner might be worried about how to keep enough spares on hand for all possible future failures. i am not one of them.
I would have poured some new bearings but I only have white metal suitable for spark ignition engines (less tin and antimony). I think there are quite a few CS engines (on show) that have bronze or brass home-made bearings fitted in them. My tractor manuals say to just remove shims to keep clearances within spec as the bearings wear. So OK untill crank ovality is the problem.
There are other things to be careful of - like keeping the bearing straight, and lining up the three bearing crank mains. I have not come across any five main bearing cranks on scraped metal bearings but I would think there are a few. The good old Fordson standard tractors had their bearings poured into the block. No particular problem to re-white metal them these days - they are usually line bored - far easier and much quicker than scraping.
The biggest problem is geting the corrrect alloy and making sure it stays homogeneous during the pouring stages. More to it than meets the eye but not too difficult when you understand all the pitfalls. Once you have suitable jigs for a particular job they are easily repeated with just model engineering type lathes and milling machines.
And if I can't do it my local foundryman will help out for a ssuitable fee. like I say, you worry too much. These engines were designed in an age when this type of repair was normal.
Regards, RAB
