Why one and three groove valve keepers?

12many said

I recall grinding the edges on the multi-groove locks so they didnt butt together, but gripped the valve. Simple mod, a little fiddly, read about doing that from some articles or bulletin I believe back in the early 80's when there wasn't a plethora of valve choice, just worked with what you had, Worked fine.

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Really? I've never seen valve locks that butted together completely on both ends. There's always a gap. In fact, I JUST assembled a slant 6 head WITH two and four groove valves and they don't butt completely together. I've assembled a crapload or heads through the years too and so far not seen the need for that mod.