Rebuilt cm 870

[Izzyrod52]

What can I expect from an overhauled cm 870? It's a 435 with a fresh overhaul and it was just broken in last weekend. Went for a test drive and it ran very well. I'm interested in buying the truck but I wanna get some opinions here first.

[hhow55]

Perhaps your interested...........It's for sale

[tree98]

(01-28-2023 )Izzyrod52 Wrote:  What can I expect from an overhauled cm 870? It's a 435 with a fresh overhaul and it was just broken in last weekend. Went for a test drive and it ran very well. I'm interested in buying the truck but I wanna get some opinions here first.

The number one question is who rebuilt it? There are certain procedures that must be followed to get the most life out of an ISX.

Only OEM internals, no aftermarket crap inside the engine.

Counterbores must be cut and liners shimmed up to .014

The old cylinder head must be replaced with a new OEM cylinder head, not a "reworked" or "rebuilt" head. You most certainly can't re-use the old head!

The head must be torqued down and then let sit overnight for the gasket to crush, then retorqued and the final 90 degree turn on the bolts

If these things aren't done, you don't have an engine that will last a million miles without major problems. You will likely only get maybe 200k-300k before a liner breaks loose or some other reason to tear it all back down again.

Also make sure it wasn't put back together with RTV on the gaskets, or instead of the gaskets!! That's the kiss of death for an engine. Here's a recent example of this https://rawze.com/forums/showthread.php?tid=8578

Last but definitely not least, is it demandated? If so it's likely a bad program and you'll need to have that straightened out immediately.

[Rawze]

(01-28-2023 )Izzyrod52 Wrote:  What can I expect from an overhauled cm 870? It's a 435 with a fresh overhaul and it was just broken in last weekend. Went for a test drive and it ran very well. I'm interested in buying the truck but I wanna get some opinions here first.

personally, I would be scared of a truck being sold with a fresh inframe...
most shops cannot rebuild an ISX worth a damn these days.. so I would be more scared of that than an engine that was worn out.

What about all the receipts to prove everything inside was OEM only, and a brand new OEM head too. After-garbage parts inside it = nothing but a headache that has to come all apart again about 2 years from now or so.

Also, people do not tend to drop $28,000+ or more into a truck that is 17+ years old, just so that they can sell it at a loss. The whole truck of that age is not even worth more than what a decent inframe would have cost anyways.

[Peashooter67]

After everything I went through with mine these are my words of wisdom.

First is listen to what Rawze posted in response to your question.
Second. If you were not there to oversee the “rebuild” you don’t know nothing but what “they” tell you.

Here is my take with my experience to properly rebuild an ISX CM870

New head

New harmonic balancer

Rebuild your rockers because it’s easy and will save your cam but this part is not necessary

If your crank shaft is for any reason been turned to an under size GET a NEW CRANK SHAFT that is standard size

Use cumins internals “ bearings,rods,pistons,gaskets, head gasket”

Deck your block and cut your counter boars then shim your liners 15thou protrusion

Use new head bolts and rod bolts.

Put a new clutch in while you’re doing this.

Use a new oil pump and shim the regulator in the pump while you’re at it.

Be sure you have a good operating program in your ecm.

Rawse, did I miss anything?



I bought a truck because it had a fresh rebuilt motor a few years ago. As a result this motor cost me more than the truck did and just about put me out of business and I had two trucks on the road when I bought this truck.

When I first bought it it ran fine and shortly later had a serious oil pressure issue that needed up costing about 18k to find and fix the problem then 108000 thousand miles later the crank broke and I had to rebuild the motor front to back top to bottom for about another 28k or more.


If it were me I’d rather buy one that need the motor rebuilt so I can do the rebuild or be a big part of the process.
As far as this truck you asking about you pay your money and roll the diece. Oooodddsss are you will lose.

Grab your wallet and run away from this truck as fast as you can. That’s my advice knowing nothing more about the truck.


Who rebuilt the motor ?
What did they do and what is left on the list they didn’t do?

I can nearly bet and be 100% right that the harmonic balancer has never been replaced so soon you will have a broke crank shaft if it has not been replaced. That’s the end result of a bad harmonic balancer.

Your ifsm will most likely need a thorough cleaning and some repair also. If the egr system is in tact and functioning it will also need a lot of cleaning and maintenance to bring it back to proper functioning operation.