Messed up oil drain tap, Savalgable?
 

So as the title says I recently drilled and tapped my oil pan. I did this using a 3/8th npt tap but noticed I was really struggling to do it. I guess I over widened the hole as my fitting just spins and I can't get it to tighten down at all. Can I re-drill and tap using a 1/2npt to 8 an to use with my MKturbo oil line? Or am I pretty much screwed? I only went hallway up on the tap but it never seemed like it wanted to stay straight. Any tips the next time I try and tap the hole? I did half turn in, quarter out but apparently I messed something up along the way. Thanks!

What drill size did you use. 3/8npt is a 9/16 drill and 1/2npt is 45/64. When i tapped mine i just went back and forth maybe not a full half turn at a time but you can feel when you get a good size burr and need to go backwards. Then test fit your fitting multiple times while tapping until you get the proper engagement. If you go too deep your fitting wont get tight and too shallow it wont start. When you test fit you are trying to find the middle ground to where the fitting will start and only goes in deep enough to barely pass through the oil pan.

But yes you should be able to up size to a 1/2npt

I used a 9/16 drill bit with the 3/8 npt tap. Everything was going well and when I test fit it, it went a little less than halfway in but not very well. So, stupidly, I tried to clean it up a bit and get it just a tad further in but apparently I fucked up. Yes I went too deep and it won't tighten at all. The threads are really shitty too, might have been going at an angle I guess but it seemed hard with the tie rod(?) in the way. So I could re drill with the 45/64 and then just buy the proper fitting? That maybe what I will have to do. Stupid mistake and i'm paying for it in frustration

Its a real pain but you have to keep it super straight. Unhook the tie rod at the spindle if you need too it wont change you alignment specs and just kit the knuckle to pop the tie rod loose dont hit the threads or screw with pickle forks. Also the pan is real thing you only get 1 or 2 threads worth of engagement. Then when you put the fitting in use loctite 545 instead of thread tape or jb weld or any of that. 545 is actually made for stuff like this. I can even ship you a little bottle if you need i have a ton at work

Correct drill size for tapered 3/8" NPT tap is 37/64, no? It may be that you had so much trouble because you used a slightly undersized drill bit.

Tap Chart NPT National Pipe Taper Threads

I paid the money for the 37/64 bit; I've since tapped probably 6 holes in all sorts of materials and thicknesses, went perfectly every time.

Do the 37/64 unless you have a tapered pipe reamer to taper the hole for the tap. or i guess now a 23/32

I believe that is the best bit but there were a few sources I found that said the 9/16 works as well. I couldn't find the 37/64 anywhere around town and didn't want to wait for it. Probably didn't help me out being so impatient. Live and learn I suppose. Just ordered a 1/2NPT to 8an fitting for like 7 bucks so hopefully that will work for me. I'll get the correct bit this time and do my best to get it perfectly straight.

Then if that doesnt work i think this is the only option left
Weld Bungs With 1.0? Diameter Step ? Aluminum & Steel A-N Adapters | Fragola Performance Systems

Yeah but I don't know how to weld so I think that would be a problem lol. Would probably just have to source a new oil pan and then either suspend the engine or pull it unfortunately. I think I can salvage it with the 1/2 NPT to 8an. I am confused on the difference between the tapered and non-tapered pipe reamer. Googling it didn't help me. That just means if the tap I have is tapered or not? Which they are in my case

So with a tapered tap reamer you will drill your hole to the 9/16 then you would take a tapered reamer and make the hole tapered and perfectly round vs the drill bit that will give you an oval hole that is perpendicular to the surface. so the tapered reamer will match the taper of the tap and in theory give you the best pilot hole for the tap.

Without the tapered tap reamer you will drill a slightly oversize hole to account for not having a reamer so you can go into a hole that is perpendicular rather than tapered

Hope that helps

You can always go one size bigger or two sizes bigger on your oil drain. It is not critical. Bigger is actually better.

You're saying 1/2 npt would be better, or rather maybe flow more oil, than a 3/8? I went 3/8 because that's what Lars sent but that's good to know if I ever source lines and fittings myself next time. Thanks!

side note: anyone know how to shorten a drain line? Seems like it's solid metal, would I have to find a shop that could shorten it?

Can you post a picture of the hole you have right now? Going up to a 1/2 NPT fitting is a no brainer. Making the hole bigger is not.

Because you already have a large hole drilled, you may have a tough time going up to 23/32 with a new split point drill. The edges of the bit are going to bite hard on the metal, which will twist the drill around, knock you off center, etc. I gave myself a black eye this way once. Even worse, when it finally breaks through it may catch an edge and propel the bit deep into the hole and take out your oil pickup, depending on where your hole is.

I guess what I'm saying is, this is no longer a slam dunk. Unless you feel like pulling the motor to fix things that you damage, take your time and use extreme care. The "right" way to do this at this point would be to borrow a set of straight-sided reamers and progressively ream up to 23/32. If you're going back in with a split point, make a depth stop over the drill bit out of PVC pipe, go slow and stop often to check your work.

Check YouTube for videos on making -AN turbo oil lines. To shorten it you take off the fitting at the end, cut the hose shorter, and put the fitting back on. I found it to be a big pain in the ass; cutting the hose makes the wire jacket fray, which then stabs your fingers and makes it hard to get back into the fitting. Best method I found was to wrap the area tightly with electrical tape before cutting.

I used a step bit.

Thanks for the help guys! Here is a picture of the hole I currently have. I used the PVC method on the first bit (or rather the ghetto tons of electrical tape) which worked well when I punched through the first time. Where would I get a set of straight-sided reamers? I would only be using these maybe a handful of times depending on how often I have to tap the pan correct? I would rather do it more correctly this time as I had so many issues this past time with taping. Would the step bit be another option instead of the reamer? With the step bit I would have to really pay attention and make sure I didn't open the hole too large correct?

Edit: Not sure why the picture is upside down, sorry!

With a step bit you just go one step at a time and check to see if you can start the tap or not

Instead of just guessing on size with an oil fitting. Find a step bit the correct size, or turn down one to be the right size.

Or just use tons of jb weld and risk having it pull out.

Yeah I was dumb and have no excuse. I couldn't find the 37/64 in any of the 3 stores I went to and the last one had a chart that said 9/16 would also work. Didn't understand it would work but only with a pipe reamer. I won't be going the JB weld route, would rather not chance blowing oil everywhere because it came loose haha. I bought a 23/32 online for the 1/2npt fitting i bought as well. But it seems Schroedinger's way might be better, will have to do some more deciding. Step bit could work as well as Sixshooter suggested. Too many options!

Step bit is fine as long as it gets you to 23/32. If you can’t find one with that size, you could use the step bit to get you to 11/16 then just buy a 23/32 straight reamer.

God I'm a dummy. Could have got this https://drillsandcutters.com/3-8-car...-bit-qualtech/ for $8 and would have 0 headaches. Okay I'll return the bit that is coming and find a step bit or step bit/straight reamer combo that will get the job done. May still order this to have it for the next time I or a friend does this job.