Waiting to get my block, heads and crankshaft back from the machine shop. I called on the progress today and was told the only hold up was that they were assuming the valve stems were normal 11/32” diameter, and mine are 5/16”. I guess they haven’t run into this before. This is my first Ford rebuild, but I had researched the build before I started it, and had never heard of the valve stem size difference. Are my ‘62 260 V8 heads that much of a oddball?
I guess not. They said the valves that came with the kit that they ordered had the 11/32”. It just seemed a little odd that my original heads would be different than a run of the mill 289,302. It caught them by surprise. I just figured someone here might have run into this before. I kind of suspect they were making an excuse because they’re behind schedule with the completion
260 heads also had smaller combustion chambers than 289s. Early 260s had lighter connecting rods and a differently balanced crankshaft than the later 260. All 1962 are early, all 1964 are late. But I don't recall when the changeover was.
All the 260's I had were 5/16 stem, all my Ford books say 5/16 [.310]. 11/32 didn't start till 289 cube.
If you have guides that will work, run the smaller stems, that’s a little bit of airflow and less weight to move.
1964 260 engines had 11/32" nominal valve stems (actual 0.3410"), same part number as the regular 289 engines: