Home › Forum › Ask A Member › 1970’s -1980’s Evin/John 4 hp piston /rod diameter specs › Re: 1970’s -1980’s Evin/John 4 hp piston /rod diameter specs
It takes quite a bit of homework to figure all that stuff out, but basically the rod & crank set up changed around 1980. The piston did not, except in 1971, the piston rings went to two rings. The two ring design changed to pressure back style rings. That changed the part number. It also changed the sizes available. In all the years piston have been std., .020 OS, .030 OS. After pressure back rings came in the price of the rings are really expensive. I try to watch for any OS pistons I can find. I have over a dozen JW and Lightwins and love the little motors. Parts are hard to find at a deal, but you get lucky every now & then.
Dan in TN