Currently building up HS40's and wanted to note a change that Tecumseh made regarding pistons and rings. In later years Tecumseh started using thinner rings. The piston size on an HS crossed with some of the OHH engines (as does alot of other internals) so they offered that piston/rings as an alternative. It can be seen on parts listings and can be a little confusing. This is not a big deal if your getting a piston/ring assembly complete. But If say you need a piston but have rings or vice versa, the rings are thinner on the late model so parts do not interchange. This was the problem for me last year and when I needed a stock piston to replace a bad one that I needed to use .010 over rings with. I ordered up the late model piston as it was all I could find new only to find the rings I had wont interchange :doah: This change may be on all the engines, I really dont know right now but something to watch for.
Here is the difference (Old on the left)
Engine above is actually a 1969 HS40, but it was only run a handful of times in the first 10 years of its life and ended up in dry storage for the rest of its life. I decided I am going to use the new style piston and rings as the lack of any wear on the bore the stock sized rings actually do come into spec (barely) and saving the old piston for something where I need to use .010 over rings and trim to fit for a better fit as I have stashed a few sets of the hard to find oversized rings....but of course cant find new or really good used pistons to use with them :doah:
Here is the difference (Old on the left)
Engine above is actually a 1969 HS40, but it was only run a handful of times in the first 10 years of its life and ended up in dry storage for the rest of its life. I decided I am going to use the new style piston and rings as the lack of any wear on the bore the stock sized rings actually do come into spec (barely) and saving the old piston for something where I need to use .010 over rings and trim to fit for a better fit as I have stashed a few sets of the hard to find oversized rings....but of course cant find new or really good used pistons to use with them :doah:
