291 Head Differences
 

I have 2 3964291 rectangular port heads. Both are cast D 23 70. The strange thing is the heads have "HI PERF" cast into them. This may be common but I have never noticed it before. Here is a picture of what I'm talking about:

http://i179.photobucket.com/albums/w...ds003Small.jpg


Jason https://www.yenko.net/ubbthreads/imag...lins/beers.gif

Re: 291 Head Differences
 

http://i179.photobucket.com/albums/w...ds002Small.jpg

http://i179.photobucket.com/albums/w...ds004Small.jpg

Re: 291 Head Differences
 

Make sure they are both machined for the same style spark plug too.

Re: 291 Head Differences
 

2 different styles of "HI PERF" being cast the same day is interesting.
Like John Brown said, check to see if they both take the same style spark plug.

Re: 291 Head Differences
 

To my understanding, the Tonawanda foundry had multiple molds for the same head, with some having slight cosmetic differences from one to the next. I am sure some of the site members here can give a clearer answer on the subject

Re: 291 Head Differences
 

[ QUOTE ]
Make sure they are both machined for the same style spark plug too.

[/ QUOTE ]
Also, make sure they're cast for the same size valve seat...

Re: 291 Head Differences
 

They both use the same style park plugs and look to have the same size valve seats. I guess there were just different molds. Learn something everyday.


Jason

Re: 291 Head Differences
 

To be more precise, high-volume castings had multiple PATTERNS (made of cast iron or stainless steel); when sand was packed around the pattern, it created a sand mold. The sand mold was opened, the pattern was removed, and the mold was closed. Iron was poured in the sand mold, and the sand disintegrated on the "shake-out" table after cooling, when the raw casting was removed.

Each pattern was numbered and carried the casting number, casting date and hour clock; that appeared on each casting, and enabled internal traceability in the foundry back to the pattern in the event of a problem with a casting.

The casting number, casting date, and pattern number were individual brass characters soldered to a brass plate that was pinned or screwed to a recess in the pattern; the date tag was changed every day, and the clock tag was changed every hour. Photo attached of tags from the Saginaw Foundry.

https://www.yenko.net/ubbthreads/imag...lins/beers.gif

Re: 291 Head Differences
 

Cool stuff, John...