How the flywheels came to be on this engine is a bit of a puzzle. The serial numbers on the wheels do not match the engine tag, so it did not leave the factory this way. They are a set of wheels for a twin because the "factory" stamp for the #2 cylinder injection timing mark is there. The keyways were damaged at one time and the wheels were fitted for Browning tapered bushings. IIRC the wheels were machined by an Amish machine shop in Pennsylvania.
My friend George overhauled this engine shortly before the crankshaft problem. After the crank failed, some other engine was installed and this was probably a trade in. He knew that it was in good shape and was keeping it for his personal collection. Sadly I lost him about a year ago and further history on the engine went with him.
Several local Amish wood shops had Lister twins driving line shafts that ran various equipment. There were complaints that the uneven firing of the twins caused issues with the equipment and the finishes of the wood. The heavy flywheels may have been an effort to address this.
Most shops have now gone to more powerful, multi cylinder engines with hydraulic, pneumatic, electrical, or mechanical drive systems.
Regarding the pistons, Singles up to 6 and twins up to 12 HP came with cast iron pistons. When speeds were increased to 850 RPM for higher output, alloy pistons were fitted to reduce reciprocating mass, stress on the rod, bearings, etc. I do not know exactly why this engine was fitted with alloy pistons at rebuild. Perhaps it was what was available or in stock. They are standard size and like new, as were the chrome rings and cylinder bores.
Although there is a mass difference between the iron and alloy pistons, at slow speeds the effect on balance is dampened by the mass of the engine. It seems pretty smooth to me!
Bob
