Thread chaser vs tap

[RiDE]

I cross threaded the drain hole threads on my transmission today. :hmm: Only the first 3 threads on the plug look like they got cross threaded. I'm not too sure about using a tap since i've never used one before. It seems like theres a bigger chance of me messing things up more with it. Not to mention that a tap for the M24x1.5 plug is $80. :\ I have new plugs on order but can I just use a thread chaser to reform the threads on the hole or will that just strip it even more?

 

[Howard]

M24 drain hole? Damn.

 

[brblx]

european or japanese car?

generally i've found that not only do americans not use plugs that big, they also don't give a shit about giving you a trans drain plug in the first place.

chase and tap are basically the same thing. if you get a 'standard' tap, it will usually have flutes cut into it and be tapered at the end, which works fine for chasing dirty or slightly damaged threads without much worry of accidentally cutting new ones. if you've pullled half the threads out of the pan, though, you'll definately be 'tapping' and may need to go oversize (or just replace the pan- if it's stamped steel, it could be nearly as cheap as that big honkin' tap).

 

[LTC8K6]

Looks like about $30 for a tap on Amazon.

 

[LTC8K6]

http://www.victornet.com/cgi-bin/victor/subdepartments/Metric-Taps/1310.html

 

[RiDE]

european or japanese car?

generally i've found that not only do americans not use plugs that big, they also don't give a shit about giving you a trans drain plug in the first place.

chase and tap are basically the same thing. if you get a 'standard' tap, it will usually have flutes cut into it and be tapered at the end, which works fine for chasing dirty or slightly damaged threads without much worry of accidentally cutting new ones. if you've pullled half the threads out of the pan, though, you'll definately be 'tapping' and may need to go oversize (or just replace the pan- if it's stamped steel, it could be nearly as cheap as that big honkin' tap).

It's euro and its a manual tranny so i don't have a pan. :\ I tried the the fill plug on and it'll go almost a full turn only. I guess i'll be doing the tap. Should I order a plug tap or a bottom tap?

 

[RiDE]

http://www.victornet.com/cgi-bin/victor/subdepartments/Metric-Taps/1310.html

Thanks! I saw the $40 taps on Amazon after I posted the thread... but $30 is better.

 

[jlee]

Did you mess up the threads on the bolt as well as the transmission? It may be worth getting another bolt if yours is messed up at all - probably cheaper than an appropriate die to clean up the bolt.

 

[RiDE]

Did you mess up the threads on the bolt as well as the transmission? It may be worth getting another bolt if yours is messed up at all - probably cheaper than an appropriate die to clean up the bolt.

I still have one from the fill hole. It would only go in about a full turn though. I didn't want to tighten it in case I mess up the threads on the tranny some more. You think it's worth a shot?

 

[jlee]

You should be able to put it in by hand until it's threaded pretty much the whole way in..if you're getting resistance and need to put force on it, I'd clean up the threads before risking damaging it further. If you can spin it in with your fingers, it should be fine..sounds like that isn't the case, though.

 

[brblx]

wait, manual trans?

are we talking about pipe thread? was there anything gooey on the threads when you removed the plug?

you can probably fix this with just a replacement plug.

 

[RiDE]

Fill plug on the left, borked drain plug on the right. You can see where I stopped tightening it by the 3rd thread. I made sure both threads on the plug and the trans where cleaned. I really should have stopped the moment I felt it binding. :|

 

[Howard]

Nothing a plasma torch can't fix

 

[Rifter]

drill one size larger and re tap the threads completly, thats what i would do anyways.

 

[Howard]

drill one size larger and re tap the threads completly, thats what i would do anyways.

If you do this, make sure you have a way of collecting all the metal chip. Also, find an appropriate drain plug before you select the corresponding tap size.

If you use an NPT thread you may be able to get away with a simple crush washer but a straight thread will require a gasket or O-ring for sealing.

 

[5150MyU]

Clean the aluminum from the drain plug with a pick.
Swap the fill plug with the drain plug.
Looks like a pipe plug so you don't want to go running a straight tap through there.
Also a couple wraps of teflon tape on the drain plug threads can't hurt.

 

[brblx]

^yes.

your pics confirmed what i thought. those things will often feel rough even while threading properly, and it seems strange that there is no sealer. a typical drain plug has a sealing surface with a copper/aluminum washer (and should thread with your fingers); these plugs just have the threads. i would expect some type of goo applied at the factory and the usual shop method is teflon tape (wrapped in the proper direction so it doesn't bind up while tightening the plug).

also, your drain plug looks like it has already been damaged all the way to the end of the threads- though intact, the threads look distorted compared to the other plug. you might have simply unscrewed someone else's mistake.

i would get a new plug from the dealer if it's in stock. if not, an auto parts store or even hardware store may have a match to those threads. thread the new plug with a bit of lube to get the threads worked back into shape (but don't tighten all the way). then tefton tape it and ram it home. it should seal. worst case, some threads fall out the next time it gets removed; but if they were that damaged it was inevitable and you're just gonna have to go oversize.

 

[boomerang]

We'll everyone's got an opinion - here's mine...

I think you're on the right track with the rethreading idea. What concerns me is how you determined the thread size and pitch. How did you?

It's difficult to tell from the pic although it is a very good pic, whether the plugs are pipe thread or not. I'd think they'd have to be to seal as there is no other means to do so with a plug of that type. My point is that if it is pipe thread, there is no such thing as metric pipe thread. Using the wrong tap is going to take a fixable problem and make it into an enormous problem that will only be remedied by removal of the transmission and possibly replacement of the case.

Regardless, for the price of a new plug, I would trash the one with the mashed threads and buy a replacement. The dealer, when looking it up may find that the thread size and pitch is called out in his parts book. That would be some handy information to know - you know?

If you determine that it's a standard pipe tap, they are readily available. I would grease up the threads to catch any chips and run it in and out repeatedly until you've restored the threads. If you've got any experience using taps you'll know when you've gone deep enough because the resistance level will increase dramatically at the point where you're cutting brand new threads along the entire range of the tap buried in the case. With experience you could do it one try - theoretically.

With the messed up threads it will be very important to start the tap square to the surface. It's easier to do when chasing threads with a pipe tap.

Edit: The portion of the sentence I bolded is wrong. I learned something in researching this and the results are in post #28.

 

[jlee]

What's the year/make/model on the car?

There are a few different pipe threads, too...BPT, NPT, tapered or not..if it's a European car with pipe thread, it might be BPT.

 

[RiDE]

Thanks for the responses guys. The car is an 03 525i.

I really do think the damage was done one the way out the first time as it was a PITA unscrewing it. I'll be picking up the new plugs tomorrow.

Thanks for the heads up about it being a pipe thread, I didn't even know what a pipe thread was before this thread. :sneaky: I have a bottoming tap on the way though... I guess it'll be going back. Can I use the first few threads of the straight tap just to reform the inner threads on the hole or is it a bad idea?

I found the thread size from the spare parts catalog:

Screw plug M24X1,5 23117527440

 

[Howard]

Thanks for the responses guys. The car is an 03 525i.

I really do think the damage was done one the way out the first time as it was a PITA unscrewing it. I'll be picking up the new plugs tomorrow.

Thanks for the heads up about it being a pipe thread, I didn't even know what a pipe thread was before this thread. :sneaky: I have a bottoming tap on the way though... I guess it'll be going back. Can I use the first few threads of the straight tap just to reform the inner threads on the hole or is it a bad idea?

I found the thread size from the spare parts catalog:

Screw plug M24X1,5 23117527440

If you have enough clearance behind the hole you can use a straight tap to clean up the whole thing.

MAKE SURE the threads on the tap are fully engaged in as much of the existing female thread as possible and produce a perpendicular (in both planes) tap.

EDIT: Unless the threads are corroded, which in your case they didn't seem to be, unscrewing is very unlikely to cause damage. The plug might've been cross-threaded the first time it went in.

 

[boomerang]

If the first few threads of a tapped hole are all messed up, the ideal tap to use would be a taper tap. Unfortunately, they're called different names. This type of tap would not have fully formed threads at the end. That makes it easier to start in an untapped hole, or in this case a tapped hole with messed up threads.

A bottoming tap would be the worst to use in this instance. This type of tap has full threads right to the end. Starting it in messed up threads will be difficult. It's important to remember that you don't want to cut a new set of threads, you want to clean up what's there. It will be very difficult to do this with a hole with messed up threads and a bottoming tap.

Here's an illustration that I hope will help. It's a little hard to read though.

Using the nomenclature in the illustration, a Taper tap would be ideal. It has a nice long lead into full threads. Easier to get it started straight and true and pick up the existing threads. The Plug tap is second best. The bottoming tap the worst. My guess is that a bottoming tap would pretty much guarantee failure in this instance.

If you cut a second set of threads, you will never get the new plug to seal. Cleaning up the existing set of threads is of the utmost importance.

Remember too, that it's a pipe thread. It's possible to tap it too deep to where the plug will not bottom out and seal the threads. You want to clean up the existing threads, but by no means do you want to go two or three turns deeper which will just make the hole larger. It's tapered, the deeper you go, the bigger the hole gets. I hope that makes sense.

If it's truly a pipe thread and IMO it pretty much has to be, your choice of taps will be limited. A pipe tap by it's very nature is tapered. This will be very helpful in getting it started.

Some background on me. I was a Die Maker for 30 years and drilled and tapped all the time. Many, many times on a daily basis.

As a side note, there is such a thing as a straight pipe thread. I've heard of it, but have never seen such an animal. I have no idea how a straight thread would seal. I believe that it doesn't rely on the threads for sealing there is a sealing surface provided that does the actual sealing. No sense going into all that here. That plug you provided the pic of has no other means of sealing and must be a pipe thread. That's been the standard for manual transmission fill and drain plugs for ages. It's inexpensive and effective.

 

[LTC8K6]

http://www.pelicanparts.com/bmw/techarticles/101-Projects-46-Diff-Fluid/Pic1-01.jpg

 

[Squisher]

Yeah, boomerang's got it, tapered pipe thread. A great thing about pipe threads is you can keep making them bigger, within reason.

.
EDIT: Unless the threads are corroded, which in your case they didn't seem to be, unscrewing is very unlikely to cause damage. The plug might've been cross-threaded the first time it went in.

You're right to a point. Not so much corrosion, but threaded stuff installed dry and used in high heat conditions can do this. People call it picking up a thread. It's more of a heat weld. Never would happen if people used anti-seize, never would happen to a pipe thread, and never would happen in the oily conditions of a transmission.

 

[Howard]

Yeah, boomerang's got it, tapered pipe thread. A great thing about pipe threads is you can keep making them bigger, within reason.

But an M24x1.5 is straight...