When to expect a dropped liner cm870

[Chamberpains]

Make your own crystal ball. Grab a sample of the fluids, oil and coolant have them tested. Get A full abuse history and any other information you can pull off the ECM. All very legit things you can demand to have up front. Ask nicely or pay the owner a couple bucks to pull the valve cover up take a look at the overhead make sure your cams are good. Low miles on an old truck you may get what we call parking lot rot on them. Or real high idle time and low oil pressure has whooped them out. You'll want to see them

[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.

[Hammerhead]

(04-03-2018 )Rawze Wrote:  ...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...

There is so much more to this than most guys realize.
I clearly work my engine harder than most.
The Aussie guys clearly outwork me without hardly trying.

I never pull to 1400. I always try and shift before 1500 or above...16-1850 is my preferred range when pulling bigger hills.
I run loaded 55-57 mph at 1620-1670 rpm in 17th gear.
I run empty ~60ish at 1500 in 18th.
When I did my inframe I had no liner fretting. It was before I found this sight, so I didn't know to cut the counterbores and raise my liners to 0.015", so they are still set at factory 0.010" and I know I'm living on borrowed time...

[Hammerhead]

Don't know what going on here?
My whole post won't show up?

Here's the simple science of it...

We have a nice big pile of wood we're going to burn.
We've doused it in gasoline!
We have a 10' trail of gasoline away from the big pile so we don't get burned.
We light a match and drop it at the very start of our gas trail 10' away from the pile...

Ignition is NOT combustion.
Ignition is point at which the fuel source first starts to burn, there is NO thrust being applied to the piston at this point. This is the match igniting the start of the 10' trail...

The 10' gas trail is the speed of our flame front, and this duration is wasted energy we cannot harness in any way, but it's a necessary evil...

Now the flame reaches our gas soaked pile of wood, and WOOSH! We now have combustion! Thrust is now being transferred to the piston and we are harnessing power from our energy source.

Now the wood ignites and we have duration to our combustion, this is the power we want to harness the most.

In our trucks we are burning diesel. Without adding a supplemental or alternative fuel source, it is impossible to increase the speed of the flame front. This duration of the crank rotation is complete waste, so how do reduce the waste? We cannot increase the speed of the flame front, so we reduce the distance the flame needs to travel and we have reduced the wasted duration, or increased the response! So how do we reduce the distance the flame front travels? The simple solution is to reduce the size of the combustion chamber...or in laymans terms, increased the compression ratio. Just like making the 10' trail 5'.
Now by increasing the compression ratio we have achieved a quicker response and reduced the wasted portion of crank duration, however YOU CANNOT REMOVE THE WASTE, ONLY DISPLACE IT! So now instead of say 10° of duration from ignition to combustion, we now have 5°...but the higher compression means INCREASED RESISTANCE during the compression stroke!
Pistons move vertically.
Crankshafts rotate.
The two different forces transfer energy to each other via connecting rods...
Con rods rock at the wrist pin end and swing at the crank end...
This different energy ultimately transfers to the connected parts.
That means the con rod forces the piston that wants to travel vertically to rock slightly and creates sidewall thrust against the liners. The more we increase the compression ratio, the greater the resistance, therefore the greater the sidewall thrust...remember you cannot eliminate the waste, only displace it. This is where it gets displaced to!

Now we're going to add common rail injection to this vicious cycle...
In an 871 and older engines the fuel is injected pre-combustion with duration only into very early combustion BEFORE peak cylinder pressures have been reached.
In common rail engines the fuel system creates such extreme fuel pressures that fuel is injected THROUGHOUT the combustion cycle! Thereby INCREASING cylinder pressures!!! Directly to our now higher sidewall thrusted piston!!! Compounding the problem...

This is why raising liner heights to 0.015" is effective. The increased height clamps the liners down harder because the head gasket hasn't reached full crush compression before full clamping force is achieved. This increases the ability of the liner and block to resist the increased sidewall thrust by transferring the thrust energy into a larger percentage of the block.

All of this happens in a matter of time.
Time in an engine is measured BOTH;
-in actual time (milliseconds)
-and duration of the crankshaft
You cannot reduce duration of crankshaft, so this part happens regardless...
[i]However, YOU!!! can reduce the actual time! By downshifting and increasing your engine RPM's, you reduce the burn length, thereby reducing the sidewall thrust time requiring less resistance time and increasing the lifecycle of the engine.
Lugging an engine, does the exact opposite...