Flea
Member
- 457
- 10
- 18
- Location
- Northeast TN
Hey everyone. Been a while since I have posted. I wanted to share this with anyone having similar problems.
Long post with information. Due to level of grease and contamination, unfortunately no pictures of the process. Picture of the truck is all I have for now (4th of July).
I have a 1991 M923A2, obviously Cummins 8.3 6CTA. The truck has had blown exhaust gaskets for some time, and they have gotten progressively worse. Not wanting to dive in to the 30+ year old gaskets and manifold bolts led to me putting it off time and again. I knew it would be a pain. This weekend, I ripped the bandaid off and went to work.
The back story is my EGTs have steadily rose to where I was on the worry gauge unloaded (1200+ easy on flat ground while accelerating). I would also only peak at around 12 PSI while under full throttle. Obviously not good.
The blown gaskets reduced drive pressure on the turbo just exactly like how a boost leak on the pressure side would cause similar symptoms.
You will need a decent impact gun, propane torch, PB blaster, 15 and 16mm sockets, some long extensions, and plenty of time. Plan on a hammer, flat blade screwdriver, and some assorted wrenches of varying sizes. I used a couple adjustable wrenches to good effect. A good breaker bar and a torque wrench are a must. Copper anti-seize.
The exhaust bolts are metric, M10x1.5, and factory is 65mm. I bought 70mm, because the new style Cummins exhaust gasket (part number 3932063) is significantly thicker. They worked perfectly. I also got a bolt with a shoulder, rather than a standard head.
I soaked all the bolts in PB blaster and worked the impact gun back and forth. This worked like a charm! 10 of 12 came out with little to no fuss. Given how much of the bolts had worn away with rust, this was a blessing.
Now, you will be removing the downpipe from the turbo, the turbo oil feed and drain lines, the alternator and mounting bracket, thermostat housing, and upper radiator hose. You will have to drain the coolant because of this. Plan on all of these gaskets, because they are also 30+ years old. I left the turbo on the manifold to simplify some things and to avoid the turbo gasket, which was fine. I was really concerned about twisting one of the studs off, which would have meant a new manifold.
When the manifold was off, I inspected the turbo (no damage, no noticeable shaft play), and I used a wire wheel to clean up the mating surface on the manifold and cylinder head.
If you find you have broken a bolt, don't panic. Plan on an extra hour or so. You will need a drill, some GOOD drill bits, center punch and good quality taps. If you have a welder and can MIG a nut onto the broken bolt, even better. I don't, so I had to do it the hard way. Center drill the bolt out progressively larger until you can re-cut the threads in the head, or until the bolt fails and comes out. An extractor kit did not work for me, YMMV.
Two days, 10 hours total, taking my time through the process. I hurt everywhere, but the truck runs and sounds awesome! I cannot get it above about 1050 on the pyro, even at WOT uphill. Boost is 23+ psi, and acceleration is smoooooth and powerful.
If you have high EGT and blown exhaust gaskets, this may be your problem!
Long post with information. Due to level of grease and contamination, unfortunately no pictures of the process. Picture of the truck is all I have for now (4th of July).
I have a 1991 M923A2, obviously Cummins 8.3 6CTA. The truck has had blown exhaust gaskets for some time, and they have gotten progressively worse. Not wanting to dive in to the 30+ year old gaskets and manifold bolts led to me putting it off time and again. I knew it would be a pain. This weekend, I ripped the bandaid off and went to work.
The back story is my EGTs have steadily rose to where I was on the worry gauge unloaded (1200+ easy on flat ground while accelerating). I would also only peak at around 12 PSI while under full throttle. Obviously not good.
The blown gaskets reduced drive pressure on the turbo just exactly like how a boost leak on the pressure side would cause similar symptoms.
You will need a decent impact gun, propane torch, PB blaster, 15 and 16mm sockets, some long extensions, and plenty of time. Plan on a hammer, flat blade screwdriver, and some assorted wrenches of varying sizes. I used a couple adjustable wrenches to good effect. A good breaker bar and a torque wrench are a must. Copper anti-seize.
The exhaust bolts are metric, M10x1.5, and factory is 65mm. I bought 70mm, because the new style Cummins exhaust gasket (part number 3932063) is significantly thicker. They worked perfectly. I also got a bolt with a shoulder, rather than a standard head.
I soaked all the bolts in PB blaster and worked the impact gun back and forth. This worked like a charm! 10 of 12 came out with little to no fuss. Given how much of the bolts had worn away with rust, this was a blessing.
Now, you will be removing the downpipe from the turbo, the turbo oil feed and drain lines, the alternator and mounting bracket, thermostat housing, and upper radiator hose. You will have to drain the coolant because of this. Plan on all of these gaskets, because they are also 30+ years old. I left the turbo on the manifold to simplify some things and to avoid the turbo gasket, which was fine. I was really concerned about twisting one of the studs off, which would have meant a new manifold.
When the manifold was off, I inspected the turbo (no damage, no noticeable shaft play), and I used a wire wheel to clean up the mating surface on the manifold and cylinder head.
If you find you have broken a bolt, don't panic. Plan on an extra hour or so. You will need a drill, some GOOD drill bits, center punch and good quality taps. If you have a welder and can MIG a nut onto the broken bolt, even better. I don't, so I had to do it the hard way. Center drill the bolt out progressively larger until you can re-cut the threads in the head, or until the bolt fails and comes out. An extractor kit did not work for me, YMMV.
Two days, 10 hours total, taking my time through the process. I hurt everywhere, but the truck runs and sounds awesome! I cannot get it above about 1050 on the pyro, even at WOT uphill. Boost is 23+ psi, and acceleration is smoooooth and powerful.
If you have high EGT and blown exhaust gaskets, this may be your problem!
