I dont know how I managed to kitten this one up, but I did! I was putting my 16cm housing, 4" exhaust, and egt gauge and I messed up by drilling the egt probe hole too large. I consulted my little black handbook for the proper size drill---it said .405 or R for the 1/8 27 npt, so I took my calipers and found a drill that was this size. Apparently I didnt read the dial or the book right because its more like a through hole size. What can I do? Im hoping to find a stainless adapter for 1/8 to 1/4 npt, but has anyone heard of this????? Help!

 

Go to a 1/4 " pipe and get a pipe bushing 1/4 male to 1/8 female npt, brass will work fine.

 

Now is the time to buy the aftermarket exhaust manifold to go with the other mods. They are pre-drilled so you will not need to worry about that little mistake again...

 

I second that. Tons of adapters out there just have to chase down what you need. No biggie a good hardware store and problem solved!

 

I'm sure they make them in stainless, but good luck finding them. Regular steel should work just fine.
What kind of probe holder do you have? You could always get a 1/4 npt one instead also.

 

Stuff happens. Measure twice cut once.

Just tap it out for 1/4 NPT & get a 1/4" X 1/8" brass reducing bushing at your local hardware store. $1.50 and you are back in business.

 

Go to Your local welding store, Ours is airgas,they can order just about any adapter in just about any material you want.

 

I agree with the suggestions to get an adaptor to reduce from ¼” NPT to 1/8” NPT but be careful with brass. Brass is an alloy of copper, zinc, lead, and nickel. Depending on the content of the alloy the melting point can be as low as 1150*F according to my Machinery’s Handbook. The brass fittings found in most big box stores are of unknown composition. Try to find one made of steel.

 

You do not want stainless or brass, you want plain old black iron, it will have the same expansion rate as your manifold and will not crack the casting when it gets hot.

Black iron is available at just about any hardware store and is the same stuff used to plumb gas appliances. Avoid galvanized, only because the galvanize will burn off and may allow it to work loose.

After you get the adapter installed nice and snug, reach in the manifold and grind off the protrusion on the inside with a die grinder. You want it flush with the cast iron manifold. Also, do not use any anti-seize compounds other than nickel based products made specifically for oxygen sensors on the adapter to manifold threads. If you use the standard products, they contain glass beads and will allow the adapter to work loose and spit out at the most inopportune time.

 

Use a 7/16 (.4375) drill for 1/4 NPT

http://www.engineersedge.com/tap_drill_chart.htm

 

Mcmaster Carr will have any adapter you need in Stainless,No big deal keep on trucken.....