Low Head

[Vrayfoster]

I have a '15 car with a low head, Unfortunately it is cracked. Now I have 3 spare heads. One, a high head, one a low head with a spark plug hole that needs repairing. Now, here is the confusing part. The last head is good, magnafluxed with no cracks but needs surfacing. It is clearly dated 7-27, yet it is a low head and It has the Ford logo cast into it. I've looked at it multiple times comparing it to a high head and to the cracked head with a 15 cast date in it. It is in fact a low head. My question is, how can it be a low head with the 27 cast date in it? Did Ford make low head replacement parts way out to '27, or do I have an aftermarket head with a fake Ford logo cast on it? Anyone know what the heck I might actually have?

[Allan]

The cast date you have may well be July 27 of any year.

Allan from down under.

[Vrayfoster]

Now that's an interesting thought.

[Wayne Sheldon]

Absolutely definitely positively confirmed by some of the top researchers in model T minutia that most model T heads made in the USA did NOT have the year as part of the casting date, if they had a casting date on them at all. Some Canadian heads had the year included in their casting dates, and a very few USA heads have been found with the year. Most of those had other oddities indicating that they were likely provided by one of the alternate suppliers.
So a 7-27 head would be a July 27 of some year appropriate for all the rest of the details. Likely anywhere from '13 to may be '16.

[Les Schubert]

Helicoil makes a repair kit for the spark plug thread (1/2” npt). I have done them over the years and they work great.

[Vrayfoster]

Thanks for the responses. I erroneously assumed the cast date was month year and that confused the heck out of me. The helicoil idea is one I have thought of but the kit is several hundred bucks. However, I will keep that in mind now knowing I have a usable head that only needs surfacing. Lang's Model T Parts (Don Lang) gave me contact information for a guy in Mass. that repairs heads using stitching. He has a picture of the crack and will let me know if he thinks it can be fixed. Also said he could repair the spark plug hole using a bushing. So, if the cracked head can be repaired and the spark plug hole repaired I will have two spare low heads of which I only need to keep one.

[Wayne Sheldon]

There are exceptions of course. However, most spark plug holes I have seen that were damaged, whether by water/rust, or forcing in a wrong or damaged spark plug? Were reparable by simply running a correct tapered pipe thread tap in. Never go any farther than absolutely necessary to make the hole work with a good spark plug. If a plug threads in too far, it could lead to problems. It is amazing how little it sometimes takes to correct a bad area of thread. Of course, if the treaded area is completely gone due to rust? And I have seen one that was that bad. It may even be beyond a threaded bushing repair?

[Kerry]

What I do is an easy fix, tap to 3/4" pipe, fit a brass plumber 1/2"-3/4" adaptor, knock 3 spots on the inside then mill off the nut of the top.

[Vrayfoster]

That's a perfect fix for my head. One set of threads are gone. Another, the spark plug goes all the way in by fingers, so 2 are in need of repairing. I had thought of doing something similar, but wasn't convinced it would work. Obviously it's a good repair. Thank you for taking the time to post your results.

[Mark Gregush]

Frank, Brilliant!!

[Susanne]

Some do, some don't. The original from my car has 12 7 15 on it, which matches both the serial on the motor (9978XX) and the casting date on the block. I have one on it now that has one with a 1913 date, I also have one that is just a month and date... I'm sure somewhere they made the change from one to another, probably mentioned in some ascension somewhere...

I remember reading in numerous sources that people would swap a later low head for an earlier one because it gave higher compression, but I wonder what the difference was... and how you can tell if you can't go by a casting date...

[Vrayfoster]

An update on head repairs: I priced a 3/4" NPT tap at $20, so tapping and installing bushings using Franks repair method will be inexpensive. Once again, thank you Frank for your response. I also checked on having the cracked head stitch repaired by a gentleman in MASS. The crack is a stress crack per him and he said it would be about $80 plus shipping. I have one low head ready to go to the machine shop for surfacing. And I will have 2 good spares available.

To figure out head volume, plug the spark plug hole and fill the chamber with water from a graduated cylinder. That will give the volume of the head. That only needs to be done on one chamber as the rest will be close. Determine the volume of the next head and you will know which one is the higher compression.