Originally Posted by russcc (Post 1910943)

Did a search on the forum here and found a set of thread chasers for reasonable money. In all my years with cars and as a machinist, I only needed one once for a spark plug hole, and that was MM. So I only need a 7/16-14. I know I can make one, but would prefer to buy it. Any sources a for single thread chaser tap. Have done an internet search and all the comes is regular taps. Thank you Fordbarners

Originally Posted by Pete (Post 1911151)

Here are few things to think about for head studs.

A thread to be properly used needs to be CLEAN bare metal.
No corrosion, rust or scale. Any of these will corrupt a torque reading.
A thread chaser is essentially an under size tap which will clean out MAJOR rust and corrosion. This device can not produce a correct size CLEAN thread. Like it or not, the laws of physics apply here.

Head stud holes in a block need to be cleaned with a standard tap which will make the thread size as it came from the factory. This operation needs to be done with a fixture that holds the tap in perfect vertical alignment or a machine such as a mill or large drill press.
If the hole does not clean to bare metal then it is too rusted/corroded to hold proper torque and needs to be repaired.
While sometimes not visible, corrosion can account for up to 20% corrupt torque readings before the thread fails.

A sealer such as high temp. RTV can be used on the dead end but a thread lube absolutely must be used on the fine thread end. The sealer should be allowed to dry for at least an hour before assembly.

Head stud holes in a block can be tested before final assembly of the engine with simple home made tools. A 3 inch diameter by 2 inch thick steel slug (BOTH SIDES PARALLEL) with a 1/2 inch hole in the center, a HEAVY HARD steel 7/16 washer, a HARD high nut and a proper length stud. You install the stud through the slug with the lubed nut and washer on top and torque to 80 for a model A or flathead V8. If the thread is good, the torque wrench will have a solid feel. No “floating” or wanting to keep turning.

Good threads will easily go over 100 if you are wondering.

Originally Posted by Pete (Post 1911151)

Here are few things to think about for head studs.

A thread to be properly used needs to be CLEAN bare metal.
No corrosion, rust or scale. Any of these will corrupt a torque reading.
A thread chaser is essentially an under size tap which will clean out MAJOR rust and corrosion. This device can not produce a correct size CLEAN thread. Like it or not, the laws of physics apply here.

Head stud holes in a block need to be cleaned with a standard tap which will make the thread size as it came from the factory. This operation needs to be done with a fixture that holds the tap in perfect vertical alignment or a machine such as a mill or large drill press.
If the hole does not clean to bare metal then it is too rusted/corroded to hold proper torque and needs to be repaired.
While sometimes not visible, corrosion can account for up to 20% corrupt torque readings before the thread fails.

A sealer such as high temp. RTV can be used on the dead end but a thread lube absolutely must be used on the fine thread end. The sealer should be allowed to dry for at least an hour before assembly.

Head stud holes in a block can be tested before final assembly of the engine with simple home made tools. A 3 inch diameter by 2 inch thick steel slug (BOTH SIDES PARALLEL) with a 1/2 inch hole in the center, a HEAVY HARD steel 7/16 washer, a HARD high nut and a proper length stud. You install the stud through the slug with the lubed nut and washer on top and torque to 80 for a model A or flathead V8. If the thread is good, the torque wrench will have a solid feel. No “floating” or wanting to keep turning.

Good threads will easily go over 100 if you are wondering.

Originally Posted by Tim Ayers (Post 1911272)

Can we circle back to the idea of using a tap and not a chaser? I understand the difference and get the physics aspect of this in regards to cleaning out all the rust and scale.

Caveat: This is what I've read, but have not actually compared. I thought the thread pitch Ford used for their head stud holes is not the same standard pitch we use today. That's why some say to make a chaser out of a an old head bolt by cutting flutes into the side.

I'd really like to know is this fact or fiction.

Originally Posted by Mart (Post 1911276)

Sort of true, but "pitch" is not the correct term.

It's just the diameter that ford held tight. You can buy taps that are correct to match the ford thread spec, but a general purpose one bought willy nilly will probably not be to that tighter spec. Someone did post the correct spec once on this forum but I can't remember who it was or the title of the thread.
I use a set of blue point thread chasers. They have proved invaluable over the years.

Originally Posted by 51504bat (Post 1911271)

Just wondering your thoughts on head BOLTS on an 8ba? I always heard never to clean the holes with a tap only to use a cleaner tap. Also per the machinist very experienced with flatheads use number 2 Permatex to seal the threads.

Originally Posted by glennpm (Post 1911305)

I would not use a tap in fear of removing parent material, BTDT. Use a thread chaser.

Originally Posted by Pete (Post 1911499)

It is physically IMPOSSIBLE for a standard tap to remove parent metal unless the thread is damaged.