New oil pressure switch doesn’t fit...318 LA

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3/8-24 is quite close to 1/8 pipe. The reason I know this, is that "in a previous life, I DIY built loading coils for a multi band HF amateur radio mobile antenna. This consisted of about 4' of 1/2 water pipe coming up from a DIY hitch receiver below the bumper, with an insulator at the base. This 4' was the bottom section of the antenna

At the top of that, I built various loading coils for each amateur band, 3.8mhz, 7.2 mhz, 14.2 mhz, and 21.3 mhz. And just used a pipe coupler and no loading coil to couple to the whip, which was a broken off CB whip. This resulted in about 8' (?) or so for the amateur 10 meter band at 28mhz.

ANYway, the loading coils were various PVC fittings and couplings or pipe glued together, with a steel pipe bushing in the top for the whip to screw onto. This was a larger size down to 1/8 NPT, into which I "chased" clear through with a 3/8-24 as that was the whip thread. You don't need to drill it, just run the tap through there. When you get done, a 3/8 NF bolt goes right in, all the way through
 
I know this is a mess,
I also have a 1/8" NPT oil sending unit hole jacked up on a 4cyl flathead.
I asked the machine shop to remove the remnants of a broken sending unit.
After all the machine work was done, fresh .080 overbore, took the engine block home.
The broken sending unit was still in the block, went back to the machine shop and a new guy removed it, than while I was standing there ran a tap into the block way too deep.
To this day I have a slight weep from the oil sending unit, the NPT threads bottom out.
NPT threads only have so much taper for sealing.
I should have just removed the broken piece of brass myself.
 
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nm9stheham said:
Thread repair compounds would be more suitable in some way, but IDK how well that would work with the top thread or 2 still apparently begin so intact. With that adapter, maybe JB Metal Weld would have been the way to go... take off the paint around there, and use JB to make that new adapter essentially part of the block. That is the best/easiest I can think of....
Click to expand...

I'm going to see tomorrow how well the Permatex set up, since the 72 hour cure time will be done. If it's as rigid as I hope it is, I might try to go with it. Otherwise, JB Weld was actually discussed with the fellas at the parts store. I shied away from it because it seemed too permanent. I wanted to be able to remove and replace the switch down the road, but that was also before I found the adapter. I'm more comfortable with the adapter being permanent and not the switch.
 
If
Righty Tighty said:
I'm going to see tomorrow how well the Permatex set up, since the 72 hour cure time will be done. If it's as rigid as I hope it is, I might try to go with it. Otherwise, JB Weld was actually discussed with the fellas at the parts store. I shied away from it because it seemed too permanent. I wanted to be able to remove and replace the switch down the road, but that was also before I found the adapter. I'm more comfortable with the adapter being permanent and not the switch.
Click to expand...
If you had to remove the switch you do have the option to leave the Permatexed fitting in place, that is if get a wrench in there to hold it, it's pretty tight back there:eek:
 
The other thing is, "boughten" pipe thread devices "are not all equal." And, with the Chinesioizaisification of parts, "it just might be" that the specs have gotten pretty sloppy. You might "dance around" and see if you can select a sender/ adapter with a tiny bit larger threads, AKA "larger taper"
 
67Dart273 said:
The other thing is, "boughten" pipe thread devices "are not all equal." And, with the Chinesioizaisification of parts, "it just might be" that the specs have gotten pretty sloppy. You might "dance around" and see if you can select a sender/ adapter with a tiny bit larger threads, AKA "larger taper"
Click to expand...

That was my theory when the adapter fit better than the switch. For once, sloppy tolerances worked in my favor.
 
What about the rest of the pipe threads in the block, did you chase them too?

There is no way that I would trust that. Not only due to the potential for leaks, but also the very real possibility that it could, with temperature and vibration, blow the sender right out..... on the highway or at the top end of the track and empty the contents of your oil pan in a hurry, oil under the back tires, engine run dry, you get the picture.

You have two options that I can see. Number one, stuff something down in the hole to plug it and drill and tap to the next PIPE size, then use an adapter bushing, or figure out exactly what thread you cut, make sure the thread is in decent shape and use a straight thread fitting with an o ring or crush gasket to adapt it to pipe thread.

FYI, i don't believe that your pipe dope will harden as you expect. It is meant to remain soft and pliable.
 
Once the sealer/locker is set, then do this for a test: Pull up hard and steady on the adapter a sender with 25-30 lbs force and hold it as long as you can; wiggle it when holding with this force. The actual force exerted on the adapter is gonna be about 15-20 lbs peak with max oil pressure.

If you do the JB Weld around the adapter, then I would suggest:
  • Leave the adapter and sealer/locker in the hole as-is
  • Cut out the present sealer/locker that is above the block; this is so that there will be no chemical reaction between the sealer/locker and the JB epoxy
  • Put a thin line of paint just at the edge of the remaining sealer/ locker at the base of the dapter, to help seal it off from the JB Weld
  • Scrape paint all around for about 1/2"
  • Clean adapter and block with alcohol
  • Apply a generous amount of JB Weld, reaching up well on the sides of the adpater
 
d55dave said:
What about the rest of the pipe threads in the block, did you chase them too?

There is no way that I would trust that. Not only due to the potential for leaks, but also the very real possibility that it could, with temperature and vibration, blow the sender right out..... on the highway or at the top end of the track and empty the contents of your oil pan in a hurry, oil under the back tires, engine run dry, you get the picture.

You have two options that I can see. Number one, stuff something down in the hole to plug it and drill and tap to the next PIPE size, then use an adapter bushing, or figure out exactly what thread you cut, make sure the thread is in decent shape and use a straight thread fitting with an o ring or crush gasket to adapt it to pipe thread.

FYI, i don't believe that your pipe dope will harden as you expect. It is meant to remain soft and pliable.
Click to expand...

When I replaced the core plugs, I didn't chase the threads since they were already in excellent condition. Those are the only other threaded holes I can think of that would be pipe threads, is that it?The only other threads I can remember chasing were for fasteners.

And you're right - the sealant I used didn't harden like I was expecting. The consistency is just that, like pipe dope. I did pull and wiggle on it quite hard (knuckles turned white and face turned red) for a good amount of time, even twisted/pulled and tried to unthread it, not a single budge. I get that under different circumstances (heat and vibration), it could behave differently. Re-tapping it is going to be my very last resort, as the engine is assembled and I don't want to drop any debris into the oil galley, even if I do stuff something in to plug the hole.

nm9stheham said:
Once the sealer/locker is set, then do this for a test: Pull up hard and steady on the adapter a sender with 25-30 lbs force and hold it as long as you can; wiggle it when holding with this force. The actual force exerted on the adapter is gonna be about 15-20 lbs peak with max oil pressure.
Click to expand...
 
On my 360 stroker years ago I could not find an oil leak but when I pulled the motor I could see that someone had tightened the oil sender to tight and cracked the block! I cleaned and ground
the crack slightly and used JB Weld in the crack.It has never leaked since. I have seen your images and it appears to be Okay but it never say never!
 
As previously stated, the tap used was probably a 3/8 - 24 [national fine] thread. The hole in the block was tapped 1/8 - 27 NPT originally. I'd remove the goop and thread in a 3/8 - 24 bolt. If it threads into the block 1/2'' deep or more that's good. Buy a short bolt of the same thread and a copper brake washer. Shorten the bolt if necessary. Drill a 1/8'' hole thru it. Weld a 1/8 NPT coupling or bushing to the hex end. Pressure test it. Screw it into the block using the copper washer as a seal. Add a sending unit.
good luck
 
Run it. If it leaks, pull it out and hit with red locktite. Or stud and bearing mount. It wont leak.
 
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