Head bolts

[Lexveen]

The rebuild of my ‘26 engine continues. I arrived at the cilinderhead. I bought a Z-head, because it’s far more efficient than the stock head because of the squish concept. But thats another topic. The topic here are the head bolts.

I bought a new set of long bolts for the high head, presuming these are right for the Z-head too. I cleaned the threads in the block with a bottom tap and blew them dry. They all looked quite good. I measured the holes and had 0,68 inch thread. When I put the bolts through the head on the workbench with the washers (aluminium head!) and an old head gasket, the underside of the heads of the bolts only protruded 0,3 inch above the head. That was not good, because with 7/16 bolts screwed in cast iron and torqued to 45-50 ftlbs, the depth must be 1,5 times the diameter of the bolt, that’s 0,66 inch. Certainly with these 100 old cast iron threads it shouldn’t be less.

I measured the Z-head, washers, a used gasket and bolts. The Z-head is 2,77 inch, the washer is 0,12, the used head gasket is 0,06 (compressed) and the length of the bolt under the head is 3,25. That indeed leaves 0,3 inch, which is half of what it needs to be. In my 26 the coilbox must be screwed to the head with three head bolts, so these three are even worse. With this length of thread, you can safely torque to 25-30ftlbs if the thread is pristine (which it never is!).

I also measured the original head, because I suppose these bolts are primarily meant for original heads. The head has been shaved some times (don’t know how often) and it was 2,7 inch. You don’t need washers with the original one, so then it would leave 0,49 inch and less under the coil box. Better, but still too short and not capable of safely pulling to 45-50 ftlbs.

My conclusion: these new bolts are not the right length. Not for the original head and certainly not for the Z-head.
I checked on the website to see if the bolts are wrong, but all the suppliers seem to sell the same length of bolts.
Reading the topics on this forum about head bolts, these also seem to be there for a long time.

Does anyone know why they sell these short bolts? I guess a 3,5 or 3,75 inch bolt is about the same price. I prefer to shorten bolts than install helicoils….

[Flivver]

I agree. I found that the vendor head bolts were shorter than I was willing to accept. I cover that topic in the Head Bolts chapter of this video, if you are interested https://youtu.be/WLcaqM89iQE

[DanTreace]

The stainless steel washers on the alum heads,(to prevent galling of the cylinder head by tightening the head bolts), have to be very thin, so don't use a thick one for sure.

And the bolt holes in the block can vary in depth and be sure to clean to the bottom of the hole, compressed air and a pick tool helps.

The new steel head high bolts will work, the short ones are the dome head late '26-27 reproductions, one or two of the block threads may be compromised and the shorter may spin out.

The Ford head bolts only reach a short way, never to the bottom of the hole, therefore only a small amount of threads on the bolt are secured. For that reason, with old bolt threads, don't apply too much torque. Only 35-40 to 45 ft/lbs can do the job of squishing the new gasket and providing the strength to keep the head tight to prevent gasket leaks. The sequence for tightening from the center line of bolts then random out is more important.

head bolts.jpg (93.23 KiB) Viewed 2661 times

[Dan Hatch]

At one time I think there was a note in the catalogs about the reproduction dome bolts were not for use with a Z head.
At least I think there was once. Dan

[George Mills]

Lex,

Your math is correct, it just doesn't work with a T because of a simple engineering decision made in 1908.

Since the 1880's, that 1and 1/2 to 1 ratio for engagement was the accepted rule for steel in cast iron. The Model T boys apparently DID follow the rule - for a 3/8-24 design! The 1st 500 or so heads apparently leaked like a sieve, and in attempts to retorque them down the 3/8-24 threads failed - apparently by 'pancaking' (my own conclusion). Was it weak iron, a hand drill with the then accepted 5% wobble of an oversized tap hole? Unfortunately, Ford never really documented the 'why's' for the fixes, just white boarded everything, came up with a solution for everything, did not look at any inter-casual relationships...FIX IT...by Friday for of demand.

This resulted in rejecting the chosen SAE Automotive thread, and taking the idea of variable bolt stretch off the table by redesigning out the two longer head bolts (water fitting) for everything that followed and coming back in with the next tap size that would fit in those stripped blocks for the head mounting. 7/16-14 ...but...they had to violate the standing 1-1/2 to 1 rule to do so, any deeper than the original 3/8-24 arrangement and they would break through into the water jacket. Wow...a band-aid fix, applied to some 15,000,000 copies, and it worked for all that time.

The bolt for a standard high head should be 3-1/4" long from the underside of the hex to the point. A normal high iron high head is 2-11/16 high if memory serves, Start there maybe? If less then they are too short...if correct the aluminum head will need something a little longer if higher??

[DanTreace]

George


Some more factory data from B. McCalley CD Encyl.:

T-483C2 Cylinder Head Bolt (7/16-14 x 3-9/32”) High Head bolt

12-19-19Adopted

3-29-21 Changed material from CD OH BB heading steel type E to CD CH wire type E.

11-4-21 Limits have been specified on the pitch diameter of threads bringing them up to date with the Bureau of Standards.

6-25-24 Removed pocket from head.

8-4-26 Changed length of threads from 1-1/8 to 3/4”.

8-23-26 Added 3/32 crown to top of head changing overall length from 3-9/16 to 3-21/32,” and specified the head to be polished, copper plated, nickel plated (400 amperes min. per sq. ft.) and color suffed. (sic, probably should be “buffed”). Specified polished surface to withstand 15 hours in 20% salt spray without rusting and removed weight per 1,000 pieces. Also specified for 1927.

From top, early '24 to '19; center 1926-27 crown head, note thread length; bottom repro nickel (s.s) crown (dome) bolt.

[Lexveen]

Thanks for your information. Now I understand how we came here and there is some logic in this. To be honest: we talk automotive development 120 years ago in a commercially environment. So I understand there are hardly records, explanations or drawings. Thats how things worked then and in smaller company’s still do (I visited several of them). What I understand too is that the 7/16 boltholes in the first batches may not be deep enough if it was designed for 3/8. The threaded part of the boltholes in my ‘26 are deep enough for 1,5 x the bolt size. Don’t know what year the were made deeper.
What I don’t understand is while the threaded boltholes are deep enough, the bolts that are presently sold for the T are still too short to make use of it. I searched the internet and found longer bolts (3,75 inch) to solve the problem, including strong washers to prevent damage to the aluminium. So for me it’s fixed. I hope the sellers start selling longer bolts…

[Allan]

To get maximum thread engagement when fitting a Z head, I swap out the T head bolts for some from a popular GM six cylinder Holden. These are long enough that I have to trim off a bit on the ends of some when they bottom out on a cleaned out T block. In their original application some of them go into the water jacket, so shortening them removes the corroded bit.
I fit the head without the gasket and cut the bolts with washers to length to almost bottom out. Then when the gasket is fitted there is a little clearance in the hole.

Allan from down under.

[Art M]

I am wondering if a hardware store grade 5 bolts that are trimmed to lenght would be satisfactory.

The bolts used with an aluminum head should be torqued exactly as recommended. By all means do not over-torque and do not lubricate unless recommended by the supplier.

Art Mirtes

[DanTreace]

I am wondering if a hardware store grade 5 bolts that are trimmed to lenght would be satisfactory.

The bolts used with an aluminum head should be torqued exactly as recommended. By all means do not over-torque and do not lubricate unless recommended by the supplier.

Art Mirtes

Art

Yes, have used grade 5, plenty good. The T is rather low compression and high strength bolts and high torque is overkill. The goal is to prevent gasket blowout or leaks. Straight fresh block and head surfaces help the most. And a light smear of anti-seize on the bolt threads is good practice to keep from busting off a head bolt that has been there for a while Surprising how much crud slips around and down the bolt, and gets to the threads. Have noticed plenty when removing a head after a few years for carbon scraping the piston tops

Repaired the spinning reproduction dome head bolt with a hardware version, on the hole by the plug. That hole had a few bad threads right where the short reproduction threads were. Sure the proper repair would be Heli-Coil. But why pull the head to just fix one hole, when a tad longer bolt would work too . So made a long shaft bottom tap brazed to an extension, for reaching down thru the cylinder head and deep into the block hole for cleaning the threads for the new tad longer bolt.

[Lexveen]

Luckily the head is new, the surface of the block is shaved and the thread in the holes is clean. So IMO a perfect start.
Where I live -The Netherlands/Europe- bolts with imperial threads are very rare. The only bolts with the proper dimensions I could find were 3,75 inch UTH grade 8 from ARP (partno 655-3750). I will have to trim these to length, but thats easy. They come together with mating washers and thats good because the stainless steel ones are to soft and to thin. Because the heads of the bolts are ugly, I have to find a way to camouflage these, but thats for later.

[Susanne]

You can have them shipped, but the recent changes in import duties and just (a least down here) shipping from the States has gotten prohibitive... (Had I known I would have thrown all my hardware in the shipping container before we moved). Example - Got an (awesome) Winfield 4v carb (there was one on the 15 roadster I took my driving test in, would pull that car to an honest 60 MPH)... Shipping the carb was $100 US, but then Duties on this end (which used to be almost nil for old car parts) was €160... Yeah, ouch!

You can round them & obliterate those grade 8 markings with the judicious use of a dremel or even a bench grinder (you're fighting the bolt's hardness with a file)... just be slow and careful! Also get the tallest bolt heads you can so you can shape them better...

Also be careful pulling them to torque, and make sure those threaded holes in the block are clean clean!!! The grade 8 bolts are hard and strong enough they will pull the threads right out of the cast iron.

[Lexveen]

Some pictures.
The one with the protruding thread is without washer, head gasket and coilbox. It will never be more then that.

[Lexveen]

I just received the longer bolts. I would qualify them with “very strong (grade 8+), perfect body, ugly head”. So technically its OK, the looks neef improvement. I think of making a cap in 5/8.

[DanTreace]

Lex

A longer length in a harder bolt may be ok to use, original Ford were most likely grade 2 and old ones used over and over have been known to break off if stuck.

However….do check each block hole depth…..as they are not all drilled the same depth. They will vary in depth.

You might find such long bolt bottoms out on a less deep block hole, that wrecks the threads in the hole or won’t squeeze and seal the gasket and head completely.

[Lexveen]

Just what I did. They all go in 5/8 by hand till they bottom out. I shorten the bolts so they just don’t bottom out without the head gasket.

[Lexveen]

BTW: because they go in 5/8, then -at least in the 26/27 engines- Ford did comply with the rule 1,5D.

[DanTreace]

Lex

Very nice, you have the best follow through, those new bolts will work fine with your adjustments and checks