Hi,
They have said that in “the good old days” the blocks were allowed to settle for six or up to twelve months (at Radford, the engine plant or at Browns Lane much earlier) and the problems in the 1970’s with engine blocks was a result of haste, i. e. machining the cast iron too soon.
Cheers!
Hi, wow that seems like a long time to sit but then I know nothing about casting iron blocks!
Best,
Bob
Essentially, in the casting process the surface cools faster and different parts cool at different speeds. Machine part of that off and leave part of it in place and you’re in trouble. To counter it, the castings are put out in the sun and are given time - the more, the better. During the time the raw castings sit, the internal stresses decrease and when they are machined they stay closer to tolerances and are less likely to crack since the internal tensions have gone. I think the process is called seasoning. Point is that your block would fit a car made a while later.
Now I wonder - not to hijack it - if normalizing (heating it in an oven) would do the same, but it is very likely much too expensive when sun and cold do the same job for free!
I’m sure it would.
D’ya suppose those blocks rust while sitting somewhere aging?
I‘m sure they do but this is before machining so I believe it won’t matter much?
If at all. It’s cast iron, so…
I had remembered something:
Instead of casting new blocks for their turbocharged F1 project, BMW only used old ones to that had done more than 100.000 kilometres. The idea was that all the stresses of the casting process would have been sorted out: if an engine block would break, it would have done so already. Or as Paul Rosche, who was in charge of BMW’s racing engine department, said about these blocks: “They are like well-hung meat.”
Even more remarkable was the process to strengthen the block’s composition. Not only were the blocks kept out in the cold and rain, but it’s also rumoured that they were peed on by the engineers. As strange as it may seem, urine has a nitriding effect as it contains compounds which form hard crystals on the surface of metal. Sword makers in the Middle Ages discovered that steel blades quenched in urine were harder than those that weren’t.
On a completely different material, I know that certain plastic components are boiled after they have been moulded. Perhaps a similar process?
Never heard of it, but sounds like normalizing (or more like tempering) for plastics is a thing!
https://www.sinomould.com/Why-Nylon-products-need-to-boil-1606.html
When you quench harden iron you need to temper it so it becomes a lot less brittle on the expense of some hardness.
When you want to soften it you need to heat it longer or differently so it can reorganize itself.
Copper is different, if you want to reuse your copper shims (think oil changes) just heat them up and let them cool or quench, they don’t mind. Disclaimer, that’s all I know.
I‘d say it’s very closely related, boiling and seasoning. Sorry 
Hmmm. Think there’s be any benefit in boiling 3D printed plastic parts?
About 40 years ago I worked at a company that made high security safes and the very large vault doors that you see in the big banks and part of the mechanism that operated the locking bolts on the safes had a ‘plastic’ gear wheel which was the part I was thinking about and I’m sure you’re right David, that it was boiled in water to take away the brittleness so that it didn’t shatter. IIRC they were boiled for something like 12 hours.
When I say plastic, in fairness it was more like a nylon type material but I don’t know the composition exactly,
Bob
I was always lead to believe it was general “ weathering “ that reduced the stresses?
Riley Cars Ltd used to bury the blocks for a few years, so no sun involved there!
As a side note, when Browns Lane was knocked down, they found ca 50 pcs of 4-cyl XK blocks that had been there since the early 1950’s, possibly just moved from Foleshill, they had been somewhere outside for ca 60 years!
I don’t know what happened to then, I would imagine they were sold to collectors, even I could have bought one. 
(I would assume they were just the cast blocks, never machined as the XK100 never entered production.)
Cheers!
I’ve done a quick google search and from what I’ve read there it was the Chinese who came up with the method to make cast iron way back in antiquity. They also developed the process to anneal the surface of the castings by subjecting them to an oxidising atmosphere.
I guess that Sir William Lyons learnt the lesson from the Chinese 