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383 Oil Pickup Thread Help

Ok, so the situation seems much better. I bought a little brass plug to test so I wouldn't mangle the threads anymore doing attempts. It originally would barely thread and get stuck a thread or two in. After chasing with tap and break in oil (I find the zinc helps form threads and reduces tap breakage), its fitting much nicer with way less resistance.
I still think it may be a bit tight, and from the other engines I've built, Ive never found this to be an overly hard operation. Maybe the extra torque from the pickup tube makes it easier.
I think what I may try if it still feels tight, is to chase it with a NPS tap right at the top because thats where the damage seems to be. Its only really gumming up at the top of the tap, where the NPT tap gets wider. Since I don't think it's damaged really bad deeper in the threads, it may be worth it to go for the wider diameter NPS at the top. Or I may just keep going slow with the NPT tap.
I feel ok with it right now to stop and play the patient game until my 2 replacement pickup tubes arrive. Going to go extra careful and I feel if I can get it threaded in a good amount, even if its tight, itll be more manageable.
I'm wondering if I should chase the pickup with a dye. Thoughts?

EDIT: Pic makes it look a little cock eyed. It is sitting perfectly level and with the same amount of engagement on each side.
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If you've already ordered a pickup tube I'd just wait for it.... I'd also probably run the tap in a little deeper... Pipe taps being tapered will thread in a few turns before they get to the diameter you want & when you hit that point the torque will go way up... Just stop when the torque goes up...
 
If you've already ordered a pickup tube I'd just wait for it.... I'd also probably run the tap in a little deeper... Pipe taps being tapered will thread in a few turns before they get to the diameter you want & when you hit that point the torque will go way up... Just stop when the torque goes up...
:thumbsup:
 
the threads are factory 3/8" STRAIGHT pipe thread. not the common hardware store pipe thread. the thread pitch is the same between straight and taper.
 
the threads are factory 3/8" STRAIGHT pipe thread. not the common hardware store pipe thread. the thread pitch is the same between straight and taper.

Yeah, that's where I get the back and forth haha. Some say straight (NPS) Some say not (NPT). Luckily using an NPT tap won't hurt it then since it's tapered anyway. Pitch and number should be the same.
 
the threads are factory 3/8" STRAIGHT pipe thread. not the common hardware store pipe thread. the thread pitch is the same between straight and taper.

Lew, is the block a straight thread too? When I tap for the 1/2", I use the straight tap in the block. I guess I could go check, but I don't think I have a 3/8 straight pipe tap.
 
Lew, is the block a straight thread too? When I tap for the 1/2", I use the straight tap in the block. I guess I could go check, but I don't think I have a 3/8 straight pipe tap.

Wouldn't the only difference be you'd have to cut deeper if they're both straight? It would make sense that the bite I am getting on the tap is about from the 3/4 mark and up. The taper is getting bigger and engaging with the straight pipe threads. Although, if you think about it, depending on how deep you tap that hole and the original angle they used in that tap, that oil hole could be like, half straight, and half tapered. The deeper you cut, the further down it pushes the taper.
 
Guess I'm now confused, what a surprise LOL. If the block is tapped NPS why does it tighten up with depth? It acts like NPT in the block would with an NPS on the pickup.
 
Lew, is the block a straight thread too? When I tap for the 1/2", I use the straight tap in the block. I guess I could go check, but I don't think I have a 3/8 straight pipe tap.
it's all straight pipe thread; pick-up and block. when i sent you stuff to do your block there should have been a straight pipe thread tap included. straight pipe thread is used in machinery and taper for plumbing or other types of building applications. i got schooled on this years back by a person who built and repaired industrial machines. a taper pipe will screw into a straight pipe because the thread pitch is the same but thread contact will be different.
 
Wouldn't the only difference be you'd have to cut deeper if they're both straight? It would make sense that the bite I am getting on the tap is about from the 3/4 mark and up. The taper is getting bigger and engaging with the straight pipe threads. Although, if you think about it, depending on how deep you tap that hole and the original angle they used in that tap, that oil hole could be like, half straight, and half tapered. The deeper you cut, the further down it pushes the taper.
the taper on straight thread is noticeably less than taper.
 
it's all straight pipe thread; pick-up and block. when i sent you stuff to do your block there should have been a straight pipe thread tap included. straight pipe thread is used in machinery and taper for plumbing or other types of building applications. i got schooled on this years back by a person who built and repaired industrial machines. a taper pipe will screw into a straight pipe because the thread pitch is the same but thread contact will be different.

Right.

Of course, the pick-up is easy to verify as straight thread with a simple root thread measurements compaired to the NPT and NPS specs. I don't have the tools to measure the block. But, the way the NPT tap threads-up into the block suggests that the block might be tapered.
 
Right.

Of course, the pick-up is easy to verify as straight thread with a simple root thread measurements compaired to the NPT and NPS specs. I don't have the tools to measure the block. But, the way the NPT tap threads-up into the block suggests that the block might be tapered.
the thread count per inch is the same. the straight pipe thread has noticeably larger lead end threads than taper so it would be easy to start taper threaded pipe in a straight thread hole. i was out in the garage looking at taps, 1/2" straight vs taper, and thought about taking a picture but wasn't sure the resolution on my ancient phone would easily show the difference. this whole thing can be played with a little due to identical thread pitch but my conclusion was don't put a straight thread in a taper hole. maybe use a taper in a straight hole if you have a good thread count past the tapered threads. i tried to measure the taps i have with a digital caliper and didn't get exact numbers but did come to the conclusion that there may be as much as .040" taper difference in thread diameter between the two.
 
I would roll up some stiff cardboard (mabe a paper towel tube with a slice in it, ) and insert that into the passage to give you a good idea of the angle needed.
Then i would use an eight point socket (i have a set, you might need to buy one) that fits your new pipe tap, wrap the tap with enough tape to make the socket a tight fit, then use an extension to get access, and use a ratchet SLOWLY AND CAREFULLY to turn the tap. Use some grease on the tap to capture any cuttings, and go only a turn or less each time.
 
Yep. Just pulled out a block and checked. It's straight thread too.

And yet per the engineering manual NPS requires an O ring or gasket to seal....

Screen Shot 2021-06-01 at 1.16.52 PM.png



Makes me wonder if it's actually NPTF.....

Screen Shot 2021-06-01 at 1.22.39 PM.png
 
i checked a 3/8" pick-up and the length of the threads on the pipe had .007" taper. i checked a 3/8" npt tap's thread taper for the same distance and it was .054".
 
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