Flathead Bore Size ?

[tubman]

On this one, I used pistons from Speedway Motors I got from their "Garage Sale" section about 10 years ago. Less than $100 for pistons, rings, and pins. I was a little leery about them at that price, but bought them anyway. I took them to my engine builder, and he checked them out and said they were fine. They were 4 ring pistons (an extra oil ring at the bottom of the piston), but after several discussions with the gurus here and on the H.A.M.B., decided to run them without the bottom ring. That meant I had to have the rotating assembly balanced, but you should do that anyway. Although it has minimum hours, the engine started immediately the first time and it runs, well you can see for yourself. After replacing the Speedway oil pump with a used genuine Ford pump with a new relief spring, oil pressure is factory spec (25 psi hot idle and 57 psi hot at 2000 rpm). The compression and vacuum numbers are where they should be and I am completely satisfied with the build.

In my opinion, a 258" engine like this is actually superior to a stock bore and stroke Mercury as it has 3 more cubic inches, and lower piston speed (which is always good). If I ever decide to rebuild the 255 merc in my '51, you can bet it'll get 1/8" over pistons, even if it doesn't need them.