EGT Probe Install...
09-18-2004, 03:25 PM
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EGT Probe Install...
Hello DTR posters!
After many long hours spent on a lengthy CTD mod project, I'm nearing the end of the list. At this point, I'm ready to start on the thermocouple install.
I've done quite a bit of searching for info on the correct drill bit and tap to use for this, but have been confused by technical variations I've read.
As far as I can tell [after looking at photos on the ISSPRO website], I've got a model R658 thermocouple. The particulars are as follows: the OD of the silver probe itself is 1/4". The male gold fitting that appears to hold the probe in the manifold is 1/2"-18 NPT [according to a web procedure I found dedicated to thread measurement].
Anyway...I'm no expert on threads and such, so I'd like feedback prior to "punching into" my manifold
Have a great one,
Bill
After many long hours spent on a lengthy CTD mod project, I'm nearing the end of the list. At this point, I'm ready to start on the thermocouple install.
I've done quite a bit of searching for info on the correct drill bit and tap to use for this, but have been confused by technical variations I've read.
As far as I can tell [after looking at photos on the ISSPRO website], I've got a model R658 thermocouple. The particulars are as follows: the OD of the silver probe itself is 1/4". The male gold fitting that appears to hold the probe in the manifold is 1/2"-18 NPT [according to a web procedure I found dedicated to thread measurement].
Anyway...I'm no expert on threads and such, so I'd like feedback prior to "punching into" my manifold
Have a great one,
Bill
10-08-2004, 11:45 PM
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Follow up...
These threads are no good to anyone if the questions are never answered, and the solutions are not recorded, so here goes...
If you're installing an ISSPRO R658 thermocouple with a probe OD of 1/4,” you’ll need a drill bit index running up to at least 7/16" [for the final hole] AND a 1/4 - 18 NPT thread tap.
First, locate the exhaust manifold passages running down toward the turbocharger. As you'll see, there are two passages running together, separated only by an internal steel wall. These passages form a "double hump" at the top of the manifold. The hump to be tapped is on the left [closest to the cab of the truck].
Referenced to the seam between the manifold and the turbo flange, make a mark two inches away [toward the head] and centered on the high point of the manifold hump. Using a hardened punch of some kind [I used the spring-loaded mechanical type], make an indent in the manifold for your pilot hole.
Starting with a 7/64" bit, drill a pilot hole through the manifold. Next, drill a 5/32" hole to enlarge the pilot hole, and continue working your way up until you ultimately reach the final 7/16" hole. Once the final hole is drilled, take your time using a telescoping mechanic's magnet to retrieve as many metal shavings and particulates as possible. Obviously, wipe the magnet clean between insertions.
Using your fingers initially, lightly press the 1/4-18 NPT tap into the hole while simultaneously turning it CW. This will start the thread cut enough for the tap to stand on its own. Once it's standing, place a 1/2" shallow-well socket over the square end of the tap. Using the appropriate ratchet, carefully turn the handle CW until the threads are cut close to the bottom of the manifold hole.
As the NPT tap tapers out toward its square end, you should be careful not to cut the threads too deep. If it helps, measure the thickness of the manifold steel and transfer this measurement to your tap [by making a mark of some kind on it]. After the threads are cut, once again use the telescopic magnet to retrieve any metal shavings.
Once the metal is completely removed from the inside of the manifold, use a rolled up towel or something similar to plug your tailpipe. At this point, clear all tools and limbs from the engine compartment and BRIEFLY start your CTD. Not only will this clear the manifold, but it will probably shoot the towel out like a terry-cloth missile.
At this point, apply an anti-seize compound to the outer threads of the thermocouple assembly and, using your fingers again, start threading the outer brass fitting into the manifold. Using an appropriate open-end wrench, finish tightening the brass fitting until the end is flush with the inner wall of the manifold [do not let it protrude into the manifold passage]. After the outer fitting is installed, insert the thermocouple probe and tighten its locknut until the probe tip extends approximately 0.500" into the manifold passage.
From here, mount the thermocouple sender near the rubber firewall grommet below the master cylinder. With the sender and the thermocouple in place, run your thermocouple leads to the thermocouple and your electrical leads to the EGT gauge.
Hope this helps someone down the road,
Bill
If you're installing an ISSPRO R658 thermocouple with a probe OD of 1/4,” you’ll need a drill bit index running up to at least 7/16" [for the final hole] AND a 1/4 - 18 NPT thread tap.
First, locate the exhaust manifold passages running down toward the turbocharger. As you'll see, there are two passages running together, separated only by an internal steel wall. These passages form a "double hump" at the top of the manifold. The hump to be tapped is on the left [closest to the cab of the truck].
Referenced to the seam between the manifold and the turbo flange, make a mark two inches away [toward the head] and centered on the high point of the manifold hump. Using a hardened punch of some kind [I used the spring-loaded mechanical type], make an indent in the manifold for your pilot hole.
Starting with a 7/64" bit, drill a pilot hole through the manifold. Next, drill a 5/32" hole to enlarge the pilot hole, and continue working your way up until you ultimately reach the final 7/16" hole. Once the final hole is drilled, take your time using a telescoping mechanic's magnet to retrieve as many metal shavings and particulates as possible. Obviously, wipe the magnet clean between insertions.
Using your fingers initially, lightly press the 1/4-18 NPT tap into the hole while simultaneously turning it CW. This will start the thread cut enough for the tap to stand on its own. Once it's standing, place a 1/2" shallow-well socket over the square end of the tap. Using the appropriate ratchet, carefully turn the handle CW until the threads are cut close to the bottom of the manifold hole.
As the NPT tap tapers out toward its square end, you should be careful not to cut the threads too deep. If it helps, measure the thickness of the manifold steel and transfer this measurement to your tap [by making a mark of some kind on it]. After the threads are cut, once again use the telescopic magnet to retrieve any metal shavings.
Once the metal is completely removed from the inside of the manifold, use a rolled up towel or something similar to plug your tailpipe. At this point, clear all tools and limbs from the engine compartment and BRIEFLY start your CTD. Not only will this clear the manifold, but it will probably shoot the towel out like a terry-cloth missile.
At this point, apply an anti-seize compound to the outer threads of the thermocouple assembly and, using your fingers again, start threading the outer brass fitting into the manifold. Using an appropriate open-end wrench, finish tightening the brass fitting until the end is flush with the inner wall of the manifold [do not let it protrude into the manifold passage]. After the outer fitting is installed, insert the thermocouple probe and tighten its locknut until the probe tip extends approximately 0.500" into the manifold passage.
From here, mount the thermocouple sender near the rubber firewall grommet below the master cylinder. With the sender and the thermocouple in place, run your thermocouple leads to the thermocouple and your electrical leads to the EGT gauge.
Hope this helps someone down the road,
Bill
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