The Ford Barn - View Single Post - 7/16-14 thread chaser

Pete · 07-19-2020, 08:34 PM

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.

07-19-2020, 08:34 PM	#7
Pete Senior Member Join Date: May 2010 Location: Wa. Posts: 5,409	Re: 7/16-14 thread chaser 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.