This weekend I was able to complete the disassembly of the engine head. Compared to today’s overhead cam engines, this one is a bit different, being a one-piece head. Still, this was advanced stuff back in 1957, when the engine was first produced. The camshaft is a 2-part design, supported by 4 ball bearings and driven by a central chain.
Typical for Honda engines of the period, there is no external oil filter, but instead a centrifugal oil “slinger” which removes particles from the oil by spinning a finned chamber at high speeds, causing the particles to be thrown to the outside of the chamber instead of circulating through the engine. There was a heavy accumulation of crud in the chamber when I opened it, which required heavy scraping to remove. I suspect that this chamber wasn’t cleaned with any regularity, if ever.
I have yet to clean all the head parts, but so far I’m pleased with their condition. The valves look great, as do the valve seats. At this point I plan to clean and lightly lap the valves into their seats during reassembly. The valve guides are also in excellent condition. After taking measurements with a micrometer, the camshafts are all within spec, and at the high end of the range, too. I already have a new camshaft chain, so I didn’t bother measuring the original.
I’ve removed the iron cylinder sleeves, and will simply retire them. I’ve ordered new forged pistons and iron cylinder sleeves, which should arrive by the end of the year. The engines cases, cylinder block and head still need to be cleaned and either bead blasted or vapor blasted to return them to original appearance, after which I’ll have the cylinders machined and honed to fit the new pistons.
These engine rebuilds are lot of fun. I’ll post updates as progress is made.