No engine serial number

[brewzalot]

My first picture- hope it worked.

This was taken leaning over the engine, looking straight down at the first stud (from the front) that holds the exhaust manifold on. The number ( Z 577 ) is stamped right above that stud on the top "ledge" if you will .

[RaymondDurban]

I'm sorry to say that I am not sure what that means. I will record it within the database and see if others have the same information in the future.

[Jim Becker]

This is pure speculation. Since we know it is a replacement block, the Z 577 was probably put there by whoever installed that block. It may be to ID it as one he worked on or might be a job number. Note a slightly bigger space between the 5 and the 77. He may have date coded May '77 (reasonable for a '73 casting). If it was put there at installation time, we will probably never know what it meant.

[brewzalot]

WOW- I feel honored to have stumped a couple of pros!!!

This is actually on a 1951 U1 power unit ( as determined by Raymond) installed in my 1961 cub.

I'm sure its something along the lines of what Jim suggests- just a means of keeping track of something, possibly a dealer or mechanic and not IH. We may never know but I would be curious if anyone else has a number there? Especially the engines that were power units perhaps?