A "What is it?" Question

29FordGuy

29FordGuy

Member
I have often wondered what a particular part on the engine was for, especially since from day one it leaks a small bit of oil when the engine is running. It is a special threaded stud that protudes out of the lower block directly below the carburator and interestingly, in line with the oil pump. It is 1-3/4" long, 3/8" fine thread on the end that goes into the block, a 7/16" hex head, then capped with a 1/4" coarse thread stub. It appears that something should attach to the 1/4" stub, but what? Is this where a oil pressure sensor would go?

Can someone tell me what it is for or what does it do? Does it just screw into the block or should there be a nut and washer to keep it from loosening up and falling out and seal it from leaking oil? Thanks for your help!
 
29FordGuy said:
I have often wondered what a particular part on the engine was for, especially since from day one it leaks a small bit of oil when the engine is running. It is a special threaded stud that protudes out of the lower block directly below the carburator and interestingly, in line with the oil pump. It is 1-3/4" long, 3/8" fine thread on the end that goes into the block, a 7/16" hex head, then capped with a 1/4" coarse thread stub. It appears that something should attach to the 1/4" stub, but what? Is this where a oil pressure sensor would go?

Can someone tell me what it is for or what does it do? Does it just screw into the block or should there be a nut and washer to keep it from loosening up and falling out and seal it from leaking oil? Thanks for your help!
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This should be an 1/8th in. pipe plug. This is for an oil pressure gauge connection. Remove the part and replace it with a pipe plug and see if that does not solve the problem.

Chris
 
So, what I should have is a 1/8" pipe thread plug when I actually have this special screw that I described. This piece must have been put in later and the hole bored out to 3/8 and tapped to fine thread. I think I will look for a plug that will fit. Thanks for your help.
 
Be a little careful and make sure it isn't holding the oil pump up. Had an engine last 8 miles when the guy pulled the bolt and put in a pipe plug because the pump fell down. You can tell by draining the oil and feeling the oil pump spring through the drain hole.
 
Don,
I just tried to put in a 1/8" NPT and it was too big. Mine must be odd! It does have a 3/8" 24 NFT! Since the pipe thread is larger than the fine thread, it could not have been drilled out and tapped. I also noted in John's reply below that it could hold up the pump.

I was just looking at Les' book, Volume 1 and noticed on page 1-229 the answer to my question and cause of my leaking problem. Check the NOTE.
Robert
 
You Do realize that a 1/8 pipe tap is tapered, right?
...and that it will begin cutting the threads bigger after it's inserted about 1/3 way?
I know the 3/8 tap fits, but try the pipe tap again and you'll likely notice it comes up tight.
Enlarging the block hole (by screwing in the tap further) serves no purpose other than making your plug recess further.
1/8 pipe thread brass plugs, are commonly available everywhere...autoparts,hardware & plumbing stores, although the original is only about 1/4 high with a slot head.
 
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Yes, I do know that pipe thread is tapered, that is why it is a dry seal, but thanks for reminding me. However, it appears that someone did a mestoration and inserted a 3/8"-24 screw into the hole in absence of a correct plug. The question now that I have is did they screw up the block hole threads also? I will get a 1/8"-27 PTF plug tomorrow and try it. If it works I am saved and will order the real plug from a vendor later. Thanks for everyones help!!!
 
The book page 1-229 is incorrect! CORRECT is 1/8-27 NPT, tapered, with a .339" tap drill

3/8-18 NPT, tapered, has a .578" tap drill and is much larger

3/8-24 UNF bolt has a .332" tap drill

Both the 1/8-27 and 3/8-24 will fit is this hole diameter wise....the 1/8-24 is cross threaded

Pipe threads refer to the inside diameter of the pipe

Les Andrews books are great but we will see an ocassional typo....

Since the hole is shallow standard taps do not cut the threads enough. But if you are careful you can clean the 1/8-27 up with a standard pipe tap. Use finesse..a gentle touch and coat the 1/8 pipe tap with a seal such as those used on the gas lines and you will stop your leak.
i just went through the same situation in November on a newly purchased A the had a 3/8-24 fine thread in the 1/8-27 tapered pipe hole and I added a oil pressure gauge.

Do try to avoid drilling and taping a larger hole since the hole is so shallow the standard off the shelve taps are not going to cut enough deep threads.

I hope I have been helpful......PS you can get a 1/8 plug from Lowes or Home Depot
 
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rob mcdonald said:
The book page 1-229 is incorrect! CORRECT is 1/8-27 NPT, tapered, with a .339" tap drill

Since the hole is shallow standard taps do not cut the threads enough. But if you are careful you can clean the 1/8-27 up with a standard pipe tap. Use finesse..a gentle touch and coat the 1/8 pipe tap with a seal such as those used on the gas lines and you will stop your leak.
i just went through the same situation in November on a newly purchased A the had a 3/8-24 fine thread in the 1/8-27 tapered pipe hole and I added a oil pressure gauge.
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Thanks for the help, it was most useful. That situation you ran into is exactly what happened to me. I had a 3/8-24 fine thread forced into the 1/8-27 tapered pipe hole. I have a 1/8-27 tapered tap with a blunt nose so I may be able to fix the threads if they are mangled. I did catch the error in Andrews' book. Maybe I can get this little anoying problem fixed tomorrow. Thanks again!!!
 
When using a tap, remember they are made to remove material. This may make the situation worse. You can try making a thread restoring tap from an extra pipe plug. Use a hacksaw to cut a slot lengthwise across the threads. When this is screwed into the hole any dirt and debris will collect in the slot. This may be enough to reshape the threads. If not you will have ruined the plug without further damage to the hole. I always like to start with the most conservative fix I can. Hope this helps. Howie
 
To all that answered my querry, I put in the proper 1/8"-27 pipe thread plug and now I have no leaks! What a relief. I did not have to clean up the threads any. Thanks for everyones help. Now I just need to adjust the tappets - tappet noise. I will now need to wait until the next sunny day on a weekend.
 
29FordGuy said:
To all that answered my querry, I put in the proper 1/8"-27 pipe thread plug and now I have no leaks! What a relief. I did not have to clean up the threads any. Thanks for everyones help. Now I just need to adjust the tappets - tappet noise. I will now need to wait until the next sunny day on a weekend.
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How recently have you changed the oil and what type of oil is it? When I got my Cabriolet it had a sticky tappet. I changed the oil and put Torco 50w in it and the noise went away.
 
The engine was recently rebuilt but I have not run it much because I was working on the rest of the car. I think a tappet must have lost its adjustment. I drained the oil, added Lucas additive, then refilled and topped off with the old oil. Still tappet noise, so next is to remove the cover and check the settings.
 
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