Briggs only made a few full cast iron block models throughout their history and thier last cast iron block in 1991 in thier I/C line. If you have a rare chance to come across a cast iron block Briggs, they look similar to cast iron Kohlers. The cast iron Briggs were found mostly on industrial equipment such as heavy duty pumps, very few were used on lawn equipment other than really old stuff from the 1950's. Briggs made themselves famous with aluminum engines, (Actually Mr. Briggs went on to found OMC) and Kohler took the fame for cast iron blocks.
Aluminum does dissipate heat much faster than iron, which is why none of the manufacturers make cast iron small engines any longer, that along with the high cost of iron and fewer places sand casting iron blocks. Pure iron is very expensive now, and recycled iron just does not make the grade for engine components. Hense the cast iron sleeves that are now the norm for high HP small engines. The pressed in sleeve gives the cylinder wall durability that is needed, the aluminum block heat dissipation needed along with making a much lighter small engine. Crankshafts and cams are still cast iron for durability. Some of the smaller HP small engines use Nikasil (Nickel alloy)coated cylinder walls instead of iron liners. GM tried this stuff in a car engine once with the first Vega 151 4 cylinders, and it failed horribly, but it works OK for low hour cheap small engines.
Are the new lined aluminum small engines better than the old cast iron blocks? In some ways yes, they do run cooler, often use less gas, have less emissions, and initially last just as long if not longer. On the other hand cast iron blocks can be overbored multiple times, giving them a much longer lifespan.
It is rare for anyone to bother attempting to overbore a lined cylinder in an aluminum engine, and not often recommended. Once a lined aluminum engine wears out, it is best to just toss it in the scrap pile. Although cast iron block small engines are not made any longer by anyone I know of, new old stock ones can still be found at places like Small Engine Warehouse, but be prepared to pay a pretty penny for one, for instance a Kohler Magnum 18 twin that only has cast iron cylinder jugs fetches around $2000.00.
I would have to say as far as bearings go that hands down the bearings in new engines are far better than anything in a classic engine. Bearing technology has become much better in recent decades, and is one of the factors why it is not uncommon for an automobile engine to run 200k miles today, where it was rare for one to go to 100k miles just 30 years ago.
-Fordlords-
