MTFCA Forum

I'm trying to help a friend get his new (to him) Model T ready for the Michigan Jamboree next week. We had to pull the head and in doing so, became suspicious of the head bolts.

They are obviously not original and we question whether they are shorter than they should be. The car is a 1922 with what I think is a high head. How long should the bolts be and conversely, how far should / can they extend into the block? The ones we have are about 2 1/2 inches long.

My friend has been working hard to get his car to the Jamboree, even if it's only to drive around town. Your help and advice will be appreciated.

Typically, the head bolt can thread into the block about 1/2” to 5/8” depth.

The bolt lengths vary on either a low head or high head. But for safety, clean the bolts holes to the bottom to get rid of crud. Then measure each hole with a small dia. stick from the head bolt surface to the bottom of the hole and compare to the bolts to be sure the bolts cannot bottom out.

Sounds like you have a low head.
The front head bolt will be considerably lower than the water outlet bolt. A high head, the bolt is about even with the outlet threads, with the head bolt in the hole.

Use a bottoming tap to be sure the threads are clean and blow out with air.

In addition to the above, make sure the bolts do not bottom in the block. Temporarily put the head on the block without a gasket, screw in each bolt and make sure the bolt shoulder contacts the head and not bottoming in the hole.
Art Mirtes

All good info. One question I should have asked. The bolts in it are grade 8. What grade bolts should be used?

If they are grade 8 bolts, they are replacements. The above checks will tell you if they are long enough. You need as much thread engagement in the block as the holes will allow.

Allan from down under.

JMHO but no need for grade 8 head bolts. I've seen my share of stripped threads in stamping press bolster plates where grade 8 bolts have been used. The threaded holes in the block will fail before the bolts strip.

Grade 5 is good enough. Everyone thinks "maybe stepping "up" to grade 8 is better" isn't necessarily true. They may be stronger, yes, but they're also more brittle and can actually break easier. At least that's what I was told by a metallurgist guy.

A grade 8 bolt will accept about 50% more torque then a same-size grade 5. Unfortunately, the T block will not. The grade 8 bolts won't hurt anything as long as you don't overtorque them. About 45 to 50 ft/lbs is plenty.

Original head bolts are somewhere around a Grade 3 if memory serves me right, but today about the lightest rated bolt available is a Grade 5. Lots of guys apparently go to Grade 8...just because they can, but as John Codman says, don't get carried away with the torque Grade 8's can handle...

I've said it before and everyone laughs it off...but...

The 7/16 threads in the block are about 2-3 threads shy of what all the textbooks say a basic design should be. (Cast iron Blocks...Steel bolts...7/16 size = 9 threads engagement min!). Take a look, the bolt prob only has 6 or so threads that shows prior 'engagement', look at the block, the first thread usually is wobbly from prior 'on and off' and doesn't contribute much...its' not rocket science that only 6 or so hold it all together.

There is a reason that you need to be careful with torque. (I know, guys go aluminum heads and torque to 55 and claim success. How many of them and others had to Helicoil their blocks? (Rhetorical, no answer required...lol...)

I really wonder if Ford preferred stripping bolts over stripping blocks? We just over compound the issue by overthinking today?

(Dean - Nice illustration, reminds me, that guy never got around to collecting all of his sketches together so that it could be a handbook of illustrations. He got old...he bought a Mac and left the PC world behind...the software is all different...and he is a stubborn sort of guy (wink) )

On my car I have an Aluminum Z head and was told by the engine rebuilder to torque to 55, which I have. What torque do you use on the cast Iron heads?

IMO, 55 lbs/ft is very max. and could lead to stripped block threads.

Mfg. of Z head doesn’t recommend extreme tightening.