CM 870 exhaust manifold slip joints seals

[Redland1]

I ordered a new exhaust manifold and when I went to put it together I realized that the joint doesn’t take a seal on the inside but instead it takes a clamp like seal on the outside. Joints are loose. After looking at the clamp seal part number 4923996 I’m not convinced that it will seal the manifold completely or hold for too long. Anyone have experience with that type of seal ?
Also I was searching around FB and found a post where someone was having slip joint leaks on CAT manifolds and a few people recommended a putty that’s they put on the inside of the joint and at the outside edge and once heated it hardens. Don’t know if you will allow the name but it’s called Loctite MR 2000. If y’all can let me know what you think regarding going that route instead of the clamp seal ?

[Rawze]

Not sure what your asking. It is rare to see an OEM exhaust manifold joint seal not working properly on an ISX unless it was ancient and got disturbed/stressed too much when removing manifold, someone did something to it to bugger it up, or simply installed it (or replacement seals) wrong, usually facing them wrong way.

ref: https://rawze.com/forums/showthread.php?...1#pid67961

I have even seen them tortured with more than 800+HP and they did not fail.

Makes someone ask to themselves if that engine has bigger issues? ... Maybe the pressures on the manifold are running too high?... maybe due to bad delete?.. excessive abusive boost? or some other reason?. - Maybe monitor your EGT's?, oil temps?., boost levels?, exhaust pressure levels?, turbo positions, etc?.

[Redland1]

(08-07-2026 )Rawze Wrote:  Not sure what your asking. It is rare to see an OEM exhaust manifold joint seal not working properly on an ISX unless it was ancient and got disturbed/stressed too much when removing manifold, someone did something to it to bugger it up, or simply installed it (or replacement seals) wrong, usually facing them wrong way.

ref: https://rawze.com/forums/showthread.php?...1#pid67961

I have even seen them tortured with more than 800+HP and they did not fail.

Makes someone ask to themselves if that engine has bigger issues? ... Maybe the pressures on the manifold are running too high?... maybe due to bad delete?.. excessive abusive boost? or some other reason?. - Maybe monitor your EGT's?, oil temps?., boost levels?, exhaust pressure levels?, turbo positions, etc?.

My manifold uses a different style of seal than that goes on the outside of the manifold.

[marek4792]

My experience with the 870 manifolds the ends would fit kinda sloppily if you didn't have those seal rings in there if the ends are designed for them. However if you have the "press-fit" style, or even the new style. Putting a film of antiseize on the slip joint sufaces like how Rawze does for the gaskets will not only help ease of install, but also create a seal without any putty...

[Redland1]

(08-07-2026 )marek4792 Wrote:  My experience with the 870 manifolds the ends would fit kinda sloppily if you didn't have those seal rings in there if the ends are designed for them. However if you have the "press-fit" style, or even the new style. Putting a film of antiseize on the slip joint sufaces like how Rawze does for the gaskets will not only help ease of install, but also create a seal without any putty...

Mine takes the seal in the picture that goes on the outside of the manifold.

[Redland1]

(08-07-2026 )marek4792 Wrote:  My experience with the 870 manifolds the ends would fit kinda sloppily if you didn't have those seal rings in there if the ends are designed for them. However if you have the "press-fit" style, or even the new style. Putting a film of antiseize on the slip joint sufaces like how Rawze does for the gaskets will not only help ease of install, but also create a seal without any putty...

The ends on mine don’t have the groove at the ends were the seal would go.

[Rawze]

(08-08-2026 )Redland1 Wrote:  

(08-07-2026 )marek4792 Wrote:  My experience with the 870 manifolds the ends would fit kinda sloppily if you didn't have those seal rings in there if the ends are designed for them. However if you have the "press-fit" style, or even the new style. Putting a film of antiseize on the slip joint sufaces like how Rawze does for the gaskets will not only help ease of install, but also create a seal without any putty...

Mine takes the seal in the picture that goes on the outside of the manifold.

That is a really old style manifold.

right along with the concerns I had above...

- Make sure your torquing the clamp(s) properly and not over-tightening them, etc.
Over-torquing will make it too stiff and cause it to not allow expansion under high heat loads, and therefore breaking bolts along with having other issues.

I.E.> The manifold is NOT a fixed in place part. It is supposed to have a bit of movement to grow/shrink as it gets hot/cold again. - The slip joints and OEM bolt torque metalurgy and specs are for just that.. to allow for a bit of slipping and expansion to accommodate heat growth when it gets hot, and then allowing some shrinkage when it cools off.

If the joints are set too stiff then it typically breaks mounting bolts. If the bolts are over-torqued, even by a little bit, or do not have at least 1.5x thread depth engagement vs. length, then they can strip/pull out as things get hot. They also need to be OEM quality, proper length + proper sleeves, as the metalurgy of it all and torque spec on them is very specific to allow them to grow/shrink under higher heat loads.

Some of the old-school mechanics that worked on them back in the day would leave all the joints under-torqued a little bit then, get the manifold assembly up to a couple hundred degrees by idling it a bit, and then back off and then re-torque to proper spec, everything when it was somewhat hot on engines that were the sig-600 series, or for heavy haul trucks that were known to run higher EGT's.

Next question is how hot is it getting?. What are the EGT's getting to in a hard pull?. - I would suggest a pyro on it if you don't know. Temps of 1050-1100F post turbo in a hard pull is the sweet spot for the CM870 (most red engines for that matter) in a max pull.

Those old style manifolds also fall under the category of that old TSB that I mentioned above to ream out the bolt holes slightly to allow heat slippage too. I don't remember what the size was for them, not sure if its the same size as the newer ISX's or not. ... and yeah, using a very light dusting of the silver anti-sieze on the bolt threads, slip joints, and gaskets during install.

Personally however, I would upgrade it to the newer slip-joint style if possible that they had for the later models that were same joins as 570's/871's.