CM 870 Overhaul Advise

[Peashooter67]

From my personal expensive experience

Just for the basic overhaul “internals”

All Parts must “with very FEW exceptions “ be Cummins parts. Unless you want to be doing this again in short order.

1st verification of Cpl and proper ecm program that matches Cpl.. this assumes factory stock virgin motor.

1- disassembly and inspection of parts as you take the motor apart. I will also try to take it account the age of the motor/vehicle. This is a good time to buy new sensors and wire harness.
2- purchase new head
3- if crank is to be reused it must retain original size journals , if the crank needs to be turned under standard then in the long rumen you are better off replacing crank with a new one or used that is still standard size.

Warning!!!! If you turn your crank .010 under or your original crank is already .010 under standard and you use it you risk having a broken crank soon after.
4- when you buy your cylinder kit get to broke rod cap “forget proper name” they don’t squirm under hard use.
5- get new harmonic balancer , if you don’t you are looking at a possible broke crank latter on.
Get new clutch while you are at it.

In short everything except the block needs to be replaced with new.
Head
Crank
Gasket set
Cyclder pack with fractured rod caps.
Harmonic balancer
New sensors
New wire harness
Cut the deck and have your counter bores cut. When you install your new cyclinders shim them .015” protrusion.
Get new rockers and rocker shafts too. At the very least rebuild your rockers to avoid trashing your cam and new motor.

I think in general this pretty much covers it. If you get a used crank under standard you risk a broken crank.
If you get a reman head it WILL crack.

Don’t forget new thermastats for your coolant and your oil cooler while you have the motor open.