Question about EGT probe install/drilling manifold

[Bug Out]

I bought the 1/8" NPT tap today to install the EGT probe in the exhuast manifold. The tap package says to use a 11/32 drill, but the instructions from Geno's say 5/16, which is a 1/32 smaller.



Should I use the 5/16 or the 11/32 ?



The last thing I want is a hole in the manifold thats too big...



Thanks for your help.

Ed

 

[Deezul1]

I know that the 5/16 was to small for my tap and it wouldnt start

 

[Deezul1]

My machinists tap + drill chart shows the letter R which is . 339 11/32 is. 343 and 5/16 is . 312 , "R" is the correct drill for 1/8-27 pipe tap and 11/32 would prolly be ok.

 

[RJOL]

When I installed my Westach EGT, with the 1/8" probe, it called for a 5/16 drill for a 1/8" NPT tap. That's what I used, but the only way I could get the tap started was to put the tap in my variable speed drill and really push down on it to get the tap started. After I got it started (about two threads) I put it back in the hand tool and finished the tap. I was talking to a machinist about this and he said that he routinely uses an oversized drill (I think he said 1/64 over) to do the hole before tapping...

 

[dmurdock]

I used 11/32 ... it is still smaller than the tap and will allow you to thread all the way thru... If you tap a 5/16 hole, you will be putting more stress on the manifold when you tap it (and we know how brittle cast iron is... . )

 

[Eric_77]

The smaller drilled hole will result in a stronger thread as more material (and more thread depth results) is removed to cut threads. But as mentioned you put a lot of stress doing this both on tap and manifold. As this is really low stress connection go with the bigger bit to make your life easier.

 

[LarryB]

It really shouldn't put more stress on the manifold as the tap is cutting radially, not wedging itself in. The cast iron manifold is quite soft so the smaller drill should work fine. Still, I'd go get the drill speced on the tap. For the few bucks it costs you I'ts worth the peace of mind.



Also as the tap is tapered you can control how deep the fitting sits by how deep you tap. Stop taping and trial fit. If it needs to sit lower, tap a little more. Use some light oil for nice smooth threads.

Larry

 

[BigBadDodge]

5/16 just run it all the way in,



http://www.tstproducts.com/gauge_install.html



Scott

 

[LSMITH]

Drilled mine with the 5/16" bit and chucked up the tap and ran it in. Trust me, after many thousands of holes tapped the clutch on a cordless drill is far more accurate than you or I can be. Chuck up the tap and set your clutch low, go back and forth maintaining the same angle and you are home free. Just clean the drill and grease the flutes about three times as often as you think is necessary and you will be fine. Do the same with the tap and you will be fine. I have done this at least 2000 times in cast iron and has worked fine for me. Go a tad easier than you think is possible and you WILL NOT have a problem. Hope this helps.

 

[Reddog1]

Bug Out, go with LarryG.



I was a machinist for years, in a Diesel machine shop. Drill motor to turn tap? Sure people do it, but I would not recommend it to a novice, and not for this application. You can break a tap, even a pipe tap. Someone care to explain the possible results of a broken tap in an exhaust manifold?



Make about 3 or 4 turns (by hand) then back one turn, then repeat. This will clear shavings from tap. It will do a better job. Try the probe in the tapped hole, as you go, to ensure you do not go to deep. You can tap the hole too deep!



I would not use oil, it is a lubricant, and the objective is to cut.





Wayne

 

[LarryB]

Originally posted by Reddog1





I would not use oil, it is a lubricant, and the objective is to cut.



[/B]

Wow, no cutting oil? I have always found the following to be true.



The oil prevents gauling. The cutting edge will cut fine. when the cutting edge passes and the following surface rubs on the material, one product is heat. This heat can soften the metal causing it to gaul. Add in a few chips and you have a stuck tap. crank it harder and you have a broken tap. The oil helps both prevent heat buildup and carry away chips. Nice smooth accurate threads for a better seal with no problems.



Of course, we're just splitting hairs here. It's just a cast iron exhaust manifold.

 

[DRR-24V]

I'm With Red Dog !

Still I would only go in one turn, then back out 1/2 turn and keep repeating till you get the depth you want. Cast Iron should be tapped dry. (unless you can't get the chips out) ;

 

[ZEEEW]

I havent yet installed my pyro guage, but I noticed when threading plumbing pipe with and without oil, that no oil resulted in torn, chipped, broken threads, and oil made a much cleaner cut.

This was galvanized pipe though, dont know about cast iron.

My first thought would be to use oil, but different metals have different needs and characteristics. The label on cutting fluids might recommend what metals need oil. Just an opinion, easily proven wrong



And willing to learn too DRR got in under me!

 

[LarryB]

Yea, OK, I'll listen and learn. Why should cast iron be tapped dry?

 

[illflem]

Cast, brass and aluminum all tap fine without lube. Heck with the grease and magnet to clean out the chips, I just remove the turbo for tapping and put on a larger one while I'm at it. Removing the turbo is no big deal, most times the old gaskets can be reused...

 

[LarryB]

Bill, have you ever used A9? It is a cutting oil for aluminum. Once you cut with it you'll never cut aluminum again without it. I even put it on the hacksaw. Put it on a file and the file won't fill up. Works great. A good friend is an aerospace subcontractor. I told him about it 15 years ago. He tried it, now buys it by the drum. Said it cut their alum machining time by 40%.



Hey, maybe this is another of those debates, like K&N or not, Amsoil or not.



Seems I do remember something about cast iron though. I have always used oil on cast. It just doesn't make as big a difference as aluminum or even steel.



Larry

 

[DRR-24V]

LARRY B

This is straight out of The Machinist's Library:



Lubricants For Tapping



Aluminum= Kerosene or light oil

Brass= Soluble oil or light oil

Cast Iron= Dry or Soluble oil

Magnesium= Light oil & Kerosene

Bronze= Mineral oil or light oil

Plastics= Dry or Air Jet

Steels= Sulfer Based Oils



Thats what is recommended. But, use whatever works best for you. You are correct on A-9 (in the green can) Works great and smells good enough to eat.

 

[JohnE]

Our favorite is Tapmatic Cream by LPS. It cleans up nicely and it stays in place. You can even use it for drilling/tapping overhead holes.

We usually go to the larger hole size for tapping.

Removing a broken tap is really hard on the hole.



In this example, the diference between "R" and 11/32 is around the thickness of newspaper.



Does anyone use neverseize on the threads when installing?



-John

 

[Reddog1]

Nothing like a good debate. Please note the origional post about oil did not refer to cutting oil, just light oil. However, as indicated by DRR-24V, Cast Iron= Dry or Soluble oil. How many of us have soluble oil in our toolbox? I agree with several of you, however, I am still comfortable with my original post.



We might as well really stir the pot. Are we using a gun tap? Is the cast iron really cast iron or is it a high bred? What RPM are we going to turn the drill?



LarryB if you use cutting oil recommended for cast iron I can agree with you. Use light oil I will disagree. Can you do it? Yes, but not the best practice.



DRR-24V great chart.



ZEEEW you are absolutely correct, and your opinion, as stated, cannot be proven wrong. The pipe you tapped or threaded is not cast iron. The threads usually will gal and tear if you do not use cutting oil on steel pipe, especially mild steel.



Illflem do we dare tell them about using the stickiest grease we can find to prevent the chips from going into the manifold? I’ll bet you and I could agree it works great, but must be done with care. Do you have an extra one of those larger turbos?



JohnE, seldom do I not use neverseize, antiseize or similar product during assembly. This is particularly true when using dissimilar metal fasteners.



I seldom use gasket cement, just antiseize. Gaskets are easier to remove. If it leaks, I repair it without putty. I save the putty for my carpenter projects. That should ruffle a few feathers.





Wayne

 

[DRR-24V]

Added Side Note !

Whats the hardest material to tap? I vote for aluminum. There is not a Home Shop Machinist or Model Maker who has not snapped off a small tap in aluminum. With A7 it's a lot better, but unless you own an EDM you will have to scrap the part. Just rambling.