OK, there are always at least two valid opinions on anything worth discussing, so I need to ask for advice.

I see that the EGT gauges are sold with EITHER 1/8 NPT or 1/4 NPT size sensors. Seems to me it's a lot easier to snap off a 1/8 tap than a 1/4, so my initial thought would be to go with a 1/4.

BUT, are there other good reasons to go with 1/8 into the manifold? Need to get the gauges ordered up in the next day so need to find this out ASAP.

THanks!

 

Just go with the 1/4NPT thread and drill the hole 7/16 to tap.

 

A 1/8 th pipe tap is about 3/8" diameter at the point where you stop tapping plenty strong easier to pull (less force)

 

Theres little chance of snapping off a tap - drill the hole the right size, use some tapping fluid or grease and youll be alright with 1/8" .

Make sure you dont tap it too far in. The bottom of the thermocouple fitting should be even with the indside of the exhaust manifold.

http://www.piersdiesel.com/TechPyroInstall.htm

 

So a pipe tap is a different sizing from the "regular" taps I have in the box for bolts?

Sorry, it's been a long week already and tomorrow is Veterinary day for us - taking stud colt in for his pre-inspection vetting and am a bit ragged. I appreciate all of you taking time to respond

 

Yes they are different, the size of the pipe tap denotes the size of the pipe you will be threading for and pipe is designated by the inside diameter so 1/8" ID and about 1/8" walls = about 3/8" diameter OD pipe

 

I put in the 1/8 npt in the manifold. It was a piece of cake just drill the right size hole i believe it is 11/32 or 5/16 if you look on the tap it will tell you. Like it was said before a little oil or fluid will go a long way.

 

Think also of the size hole you are drilling. The larger hole is going to be more likely to cause a crack in the manifold than the smaller hole.

What I did was drill the appropriate hole for the 1/8NPT tap (IIRC, it's 5/16, but I dunno what it was), but didn't drill it all the way through. Then a started the engine and finished drilling the hole. The exhaust pressure blew all the shavings right back and nothing go into the manifold.

Then I slowly tapped the threads, using lots of thick grease and going just far enough to give the thermocouple a good anchor.

Tapping the threads too deeply is the most common mistake I see. I good reference is to just put a ring of tape on your tap to use for reference.

JMO

 

I also used a craftsman telescoping magnet to get down into the exhaust manifold after I drilled and tapped the hole to get all the little metal pieces out.

there were quite a few in there....I am glad I got them

WR

 

I would think the 1/8 NPT makes the most sense. As HOHN said, it has the least potential for damaging the manifold. And also, if so some reason you mess up the 1/8th, you can then upsize to 1/4 NPT