Has any one figured out regarding the weird casting dates that occasionaly show up on 186 heads? I have also seen blocks with M cast dates.

There is a set on Epay rite now and 1 is cast dated M 45. The cast date has a space between the M and the 45 are rite next to each other, not like normal casting dates with the month/day/year.

Whats up with this ? Anybody got any opininions? I have heard before that these are export heads, also someone posted once they could be a marine version head.
Auction # 270062499042

Thanks in Advance.

I thought I read on one of the sites recently that the M castings were when they changed over from one casting to another the first so many cast had the M and a sequence number. They checked them and if bad, destroyed them and if good were used. I am not sure of this but kinda remember reading something like that.

I thought I read on one of the sites recently that the M castings were when they changed over from one casting to another the first so many cast had the M and a sequence number. They checked them and if bad, destroyed them and if good were used. I am not sure of this but kinda remember reading something like that.

That is true.
M blocks were casting exercises at the flint foundry.
The M45 is the 45th time they changed the casting formula.

100 blocks (and apparently heads too)
were made, then some were cut apart to check quality.
If good, the rest were sent into regular production.

The NCRS did a study a few years back, they called it "M for Mystery"
I spoke with the author a few times, they have documented most of the sequence numbers.
Pretty common to find them.
:thumbsup: