When to expect a dropped liner cm870

[Rawze]

(04-02-2018 )Rig Wrench Wrote:  870 nowhere near as problematic as 871 and up. Especially at only 525 hp. I see 87ps come tgru my shop with more miles than anytbing with the least issues. Not uncommon to see 800k+ miles set at 565 and up hp. At least that I see. Theyre lower compression than 2250/2350 and I swear the block material is far harder than 871s and up

My own experiences ...

I was informed once by someone who would know that all of the original the CPL2732 CM871's started out as CM870 blocks that were converted to meet the new demand. This was confirmed to me a second time when I did my inframe as well, because I have a CPL2732 and was forced to order a "new-style" CM870 overhaul kit as per cummins themselves (had to call them to clarify all of it) or my parts warranty would have been voided. This is because they were in that transition period of offering the new liners with the brass mid-stops and the anti-carbon rings. Everyone at the dealer was confused about what kit to buy for it so we called it in to confirm it.

Considering that, my own theory/opinions are that it is more likely the extra bit of tubo and other response lag in the low end that gives them their slightly longer life-span?. That is also what makes them slightly less fuel efficient too tough. The trouble is that when you tune a CM871 with that same amount of delayed low-end response, that bit more turbo lag, and the less-fuel-effecient injection timing, the owner/driver will usually do nothing but complain about it. This is especially true of those guys who want more than 500HP+ all the time because they want that feeling of throw-back power when you get on it hard instead of having to shift to get it. - It is a case of "power and feel-good" vs longevity with the newer engines and not much more if you ask me.

Even Truck owners with factory 600/2050 engines who down-shift and use higher RPM instead of all the low-end torque always have engines that last 1 million plus vs those guys who lug them all their life below 1400. They always end up with liner issues at roughly 600k miles and it is totally predictable. This is even before you start considering custom tuning or de-mandates.

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Even considering all of this, the newer engines ARE more problematic, but I think not so much for their metallurgy. No one can deny that the CM870's last slightly longer than the CM871's. and that the CM871's last longer than the CM2250's and CM2350's. it is all the advances in efficiency, low end torque response, compression ratio differences and all the other things that have been changed combined with a sheer lack of re-design to reduce internal friction. Changes like improved rod length, offset cam, improved liner height, or other core component changes that would make a deference.

Personally, I am starting to think they are like that on purpose so that they can keep their fingers in your pockets long after the initial sale. That is what good corporate Capitalistic planning dictates these days for maximum profits. there is something in inherently wrong with any company who would brag to their shareholders that their DPF repair sales are up year after year, especially in emissions system components. Clearly that is a pattern of something NOT WORKING PROPERLY!>


One nice thing to know is that as iron ages, especially engine blocks due to heating cycles, it gets more brittle and hardens.