All this talk of the 'aluminum block' reminds me of one Oldsmobile made in the 1960s (and my 1st stepfather bought as "advanced engineering") in their 185 HP 215 CID that lasted just 21k miles before you could use it to drive away mosquitos. Someone told me that GM 'hardened' the aluminum bores (no iron liners) for that engine. Dunno for sure?
Then there was the Vega.
I wonder if any of those still run?
Found this info............
Reynolds Aluminum—which would later build the aluminum body for a rotary-powered Corvette concept for GM—developed the precise aluminum alloy required for the sleeveless aluminum engine. Designated A-390, it featured 17-percent silicon, used for its hardness and scuff resistance. While the new die casting process developed just for this engine distributed the silicon uniformly throughout the block, subsequent machining and etching then left the cylinder bores formed of pure silicon.
As noted in multiple sources, linerless aluminum engines are not problematic on their own. Audi, BMW, Mercedes, and Porsche have all used linerless aluminum engines in the years since to great success. According to Jacobsen, some pre-production Vega engines did have problems with scuffed cylinder walls, problems attributed to excessive honing pressure during the machining process; he claimed that those problems were resolved prior to production engines reaching the public.
Found this too.
After the engine had been in production for a while, customers would go back to the dealer complaining about oil consumption... the mechanic would peer down the bore scope and observe cylinder scuffing. We eventually found out that the problem had never been the scuffing of the (cylinder) bore. The real problem was the valve stem seals. They'd harden, split, fall off, and oil would leak down past the valves and into the combustion chamber. So we did some experiments. When we got an oil burner, we simply replaced the valve-stem seals, and that cured it.
That's real interesting about the Olds engine: the one my [1st] stepfather had only lasted 14 months from brand new before it used 2 quarts of oil between changes at 4000 miles (recommended then). Whether this was the valves or not, I can't say: I know they (my stepbrother and stepdad) got tired of changing sparkplugs and parked it. Mom and he divorced shortly after that, so I never found out what happened with that car?
The Vegas, though: it seemed that by 1980 their biggest use was to house a 350 Chevy block, lots of those around here in CO.