Engine/Transmission (1998.5 - 2002) Exhaust manifold shrinkage

[John Berger]

How can you tell if it's shrinking? Is there a way to measure it? I've never baselined the exhaust manifold so I wouldn't know what to compare it against.

 

[EricBu12]

A manifold wouldn't shrink but would get bigger from the heat. There have been bolts that have bent and the casting cracked. I took one look at an example and bought the ATS 3 piece manifold. It lets the head expand and contract to the heat.



I drive truck for a living and It has a N-14 Cummins in it. That truck has a Manifold like the ATS 3 piece. Good ole DC likes to skimp on equipment...

 

[Dkevdog]

Originally posted by EricBu12

A manifold wouldn't shrink but would get bigger from the heat. There have been bolts that have bent and the casting cracked.

I may be wrong here, but I was under the impression that they DO shrink. I have also seen examples, and the ones I saw demonstrated shrinkage- not expansion.



I was told that while it expands under heat, it changes the properties of the metal so that when it cools, it contracts further than its original shape, thus creating the stress on the bolts or head.



Kev

 

[Bob4x4]

Thats says it pretty good Kev. The most common problem on the 24v is cracking not so much the shrink issue of the 12v.



Bob

 

[John Berger]

OK, but is there any way to measure or do we just wait around and see if a crack develops?

 

[Dkevdog]

John- I would guess that besides the obvious (bent studs) the only real way to tell would be to have a new one laying side be side for comparison. And even then, machining tolerances could easily account for a difference in size. I've seen evidence of shrinkage first hand that was around 1/2" . How to see how much yours is or has shrunk Donno.



Kev

 

[David Oxland]

If you go to back out an end manifold bolt and it fights due to binding on the manifold rather than in the the thread hole or you can't get it started into the threaded portion again it has shrunk. Elongating the holes will get you a good deal more of life. If you just force the bolt it will eventually crack. Elongation, if necessary, is pretty simple. If I cracked one I would probably go for the ATS job



I posed the question of WHY on a Metalurgical question page a few months ago and there was no clear answer. Any metalurgists her got anything to offer?

 

[Bob4x4]

I may not be able to explain why this happens the way an engineer would but the mighty Cummins is not the first popular engine to have to deal with this. The small block Chevy has been doing this for ever. There is a readily available tool to stretch the individual runners of the exhaust manifold apart to be able to insert the bolts into the head. It happens we just have to accept that and move on. If you don't want to ante up the coin for an ATS

manifold I just so happen to have a new Cummins manifold in the box still.



Bob