Cleaning Cylinder Head Stud Threads

[Mike1291]

As I prepare to install my resurfaced head, I ran a thread chaser down each stud hole. Some were easier than others, but I was concerned about the two front ones, where the water neck mounts to. One of them was cleaned the easiest of all of them (not much resistance) and the other has a loose spot every 1/2 turn (tight until you turn at a spot twice a rotation).

This is concerning because the studs were the worst offenders to take out and one required heat. Should I be concerned about this?

 

[nkaminar]

Test install a stud in the suspect hole. If it goes in OK you are good to go. If not, use the thread chaser again or try a bottom tap. The purpose of the bottom tap is to clean the tapped holes and not cut new threads.

I am assuming you are blowing out any residue.

I use an anti seize compound for the studs that have not broken through to the water jacket and Permatex non hardening sealant on those that have broken through. I just hand tighten but assure that they go to the bottom. The anti seize compound and non hardening Permatex will allow the studs to be removed during the next go around. I do not like to use silicone gasket sealant as it is difficult to clean up. The Permatex is soluble in denatured alcohol.

 

[Bob Bidonde]

Just in case, download these slides.

 

[Fullraceflathead]

As long as you can pull the full amount of torque on the studs there I wouldn't worry about them.

 

[alexiskai]

There is a protocol developed by Brumfield for testing clamp load on block stud threads. You do have to fabricate a metal block to simulate the head but otherwise it’s pretty straightforward.

 

[Mike1291]

Just in case, download these slides.

Thank you Bob for those slides. I do have a few questions.

If I were to use RTV and not the copper gasket with crush washers, what type should I use? Should it be something like Permatex Ultra Grey? (https://www.amazon.com/dp/B000HBGI8K?tag=atomicindus08-20)

According to your pictures, when you are testing the bottom of the thread holes, you only use JB weld when there's a small crack or hole? And you only use RTV (such as the one above) when the hole doesn't hold any water?

Thanks for your help everyone.

 

[alexiskai]

Thank you Bob for those slides. I do have a few questions.

If I were to use RTV and not the copper gasket with crush washers, what type should I use? Should it be something like Permatex Ultra Grey? (https://www.amazon.com/dp/B000HBGI8K?tag=atomicindus08-20)

According to your pictures, when you are testing the bottom of the thread holes, you only use JB weld when there's a small crack or hole? And you only use RTV (such as the one above) when the hole doesn't hold any water?

Thanks for your help everyone.

Any RTV will be fine for this application. Whatever you have on hand.

 

[stevests]

This is the best tool for cleaning block holes of CRUD - there's also a high-temp. nylon stud sealant available.

 

[JayJay]

I think the most important thing to remember is that you should not use a typical tap on these holes. A typical tap (like you’ll find in the hardware store or a tap and die set) cuts threads by removing metal. Those threads are already cut into your block, and cleaning up the threads by removing metal weakens the threads. Rather, you should use a thread restoring tap (sometimes also called thread chasing tap) which cleans out the threads and re-forms them without removing more metal. A good set of thread restoring taps and dies, plus a set of thread files, will go a long way to keeping your Model A together. They are available on the river store and other places.

 

[nkaminar]

Since your head is resurfaced, there is a check to do before buttoning things up. Place the head on the block with two studs, one front and one at the rear. Do not put any nuts on but make sure the head is down flat on the block. Do not use a gasket. Hand crank the engine over and note if any of the pistons push the head up. If they do you will need to machine the pockets in the head.

The squish area, the gap between the pockets in the head and the pistons, should be close to 1/16 inch. Put some wads of modeling clay on top of the pistons and do the above test. Then measure the thickness of the wads of clay and add the thickness of the compressed head gasket. Gaskets will compress to about 80% of their initial thickness, depending on the type and brand. The 1/16 inch comes from the initial research and testing done by Ricardo in the 1920's.

Some people will advise to use two gaskets to increase the clearance in the squish area, but I do not advise that. The gaskets are not designed to be used that way.

 

[Mike1291]

Fortunately for me, I did my research and used a special cleaning chaser, and not a thread cutter. Spent $35 on it but it did a great job, didn't cut the threads like a regular tap, and still looks like new after cleaning the threads.

It was a pain getting the head on 1. Since I am working alone and 2. Someone decided to fill my cylinder head with acorns...

My local A club member told me to use the copper gasket for the water neck so that's what I plan to do, and tighten it real slow

 

[alexiskai]

The gasket vs no-gasket question on the water outlet usually comes down to a person’s experience. I’ve used the copper gasket without incident and so have many others. Still others have cracked the outlet when using it. Smaller increments in the torque sequence will certainly help.

 

[JayJay]

I've not used a gasket in favor of a thin bead of silicone the last couple of times I've been in that situation, and no leaks. That's after cracking an ear. I'm convinced.

 

[bogiediver]

... used a special cleaning chaser, and not a thread cutter.

Can you share the source of the thread chaser, please? Looking for same @ 7/8" - 18 tpi to chase spark plug holes. Somewhere the 'fine thread' standard for 7/8" diameter changed from 18 tpi to today's 14 tpi, making it challenging to find a chaser at 18 tpi.

Thanks in advance

 

[JayJay]

Can you share the source of the thread chaser, please? Looking for same @ 7/8" - 18 tpi to chase spark plug holes. Somewhere the 'fine thread' standard for 7/8" diameter changed from 18 tpi to today's 14 tpi, making it challenging to find a chaser at 18 tpi.

Thanks in advance

Bogie - for general use I have this Lang tools set from the river store. It goes up to 5/8". I am not aware of any 3/4-18 thread chasing taps, but regular thread cutting taps in this size are readily available, such as this one also from the river store. Snyders (P/N A-12407) and Brattons (P/N 17701) also stock these taps. Just be sure you get a straight thread tap, the 3/4-14 tapered pipe thread is another animal entirely.

BTW, the SAE standard for 3/4" fine thread is 3/4-16, not 3/4-14. The 3/4-14 is the tapered pipe thread pitch.

Just to recap the above

3/4-14 --- tapered pipe thread
3/4-16 --- SAE fine thread (straight)
3/4-18 --- spark plug hole (straight)

 

[Tim Ayers]

This is the best tool for cleaning block holes of CRUD - there's also a high-temp. nylon stud sealant available.

I've never seen a chaser like this. Any chance you can post a link to where you go it?

For my latest V8 head swap, I used Hercules thread sealant I got from a plumbing jobber. Worked great. Much better than ARP's.

 

[bogiediver]

brattons (p/n 17701) also stock these taps.
3/4-18 --- spark plug hole (straight)

Pic clearly shows the size of Bratton's tap as 7/8-18 (not 3/4)??

btw, the sae standard for 3/4" fine thread is 3/4-16

Agreed - 3/4" fine thread is 16 tpi; but spark plug is 7/8-18 (per Bratton's and others).
SAE fine thread for 7/8" is 14 tpi if this chart is to be believed...??


I have a 7/8-18 nut that I used to verify fitment after using an 18 tpi thread file to clean up the threads on a W16Y spark plug, and it fit perfectly.

Now looking to find a chaser (thread cleaner), not a tap (thread cutter), to clean up the spark plug holes in the head.

Apologies to OP for going off the thread topic.

 

[JayJay]

You guys got me. I didn't check the actual thread diameter on the spark plug, plus I apparently misread what OP stated. All the spark plug thread chasers I found on the interweb (plus the one in my tool box) are 14 mm/18 mm.

Regardless, it's important to keep in mind that there are many thread standards out there, even if you limit yourself to just inch sizes, and to not get them confused. We tend to get wrapped around SAE coarse and fine threads for fasteners and forget that there are others such as tapered pipe threads and special purpose threads.

 

[stevests]

The thread cleaner is available for Woods Engine tools.

 

[bogiediver]

@stevests

Googled 'Wood's (Woods) Engine Tools', got a farm implement site.

Got a link?

Thanks.