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BCIII Cummins Rebuild.

Truck Shop

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Dec 7, 2015
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Because another posted about installing cam bearings in a 3406 B Cat engine, I thought I would post this
about installation. The Cat uses a cam bearing that has a groove machined into the outside diameter so
oiling holes can be installed slightly off center of oil port in block and still be fine. Cummins is the opposite,
the bearing has no groove, the groove is machined into cam journals. So when installing oil port holes need
to be on the money, although the oil ports/rifles in block are larger, so there is leeway. The bearings are
numbered to placement in the block, I index mark the block and bearing with a paint pen, double check
alignment and drive them home. Below after installed, showing cam journal with groove and test fit.
Cam fit perfect.
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I am going to run a short thread while I build this engine, It might run a while because I'm in no hurry, and
the guy who bought it is in no hurry either. When done it should produce 465 to 475 hp.
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Truck Shop

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I just noticed this thread. Very cool. What is the engine going into?
It's going to reside in a 1986 FLC. The cab and dash on this tractor is in real good condition,
owner bought a used air ride for the rear of cab. In the future I will help him lengthen the
frame and install Freightliner {Air Liner} suspension. He only paid $2,500 for it so he has
allot or room for improvements. Funny part is he is a ex Cat truck/equip dealer mechanic,
also taught diesel. He just doesn't want to do that type of work anymore-he farms.
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Truck Shop

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Since we're on the subject of ca m bearings I have the tool to install and remove small cam Cummins rearmost brg in frame . Not likely you'll need them but ya know where to find them
I had one of those, a farmer needed to use it, I gave it to him because I haven't done a
small cam for years.
 

bam1968

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IA
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Excavating Contractor
That truck must have run some pretty smooth roads or it had some sort of a suspension upgrade if the dash is still good!!!
 

chidog

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Jun 21, 2021
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kent, wa
My fond memory's of them is the nasty to get to bolt, that they should have changed after the very first engine. Yeah it wouldn't have been easy but nice.
 

Truck Shop

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I've been asked to explain Lower Press Fit Liners. It's not what most think. Below is a photo
of naturally a counter bore machined for lower press fit liners. First off unlike people would
think the lower sealing bore with the circle and line through it has nothing to do with LPF.
The old upper press fit liners were held in-place in the counter bore where there is a arrow
pointing down and the ledge of counter bore with just a blue line.
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The area below the ledge is called the pilot bore. This area is machined so a .004 crush fit
happens when liner is pressed into block-hence-lower press fit. The standard thickness of
a standard or LPF liner flange is .352, here the counter ledge is machined to .373 to allow
for a .020 liner shim. Now food for thought-a good auto machinist will cut to .373 not .372.
because the shims used by Cummins marked .020 are actually .021. Every shim made for
Cummins counter bores are always .001 over. The liner protrusion height for LPF is .004 to .007.
Old upper press fit is .003 to .006. When done with this engine the liner height should run
.006 across the 6 liners, because of all the machine work done to this block.
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chidog

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I'm not a fan of power tools on gasket surfaces, especially the head and deck.
Cummins not as fussy as Cat for protrusion, the difference from one head vs 3.
Yeah nice to have them all the same.
Sure lots of room for improvement on all the engines, but the cost and weight would be prohibitive.
 

Truck Shop

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I'm not a fan of power tools on gasket surfaces, especially the head and deck.
That deck had light rust from setting, so dusted with rolllock. It all depends on who is doing the cleaning. And I 've probably more than likely built more engines than you plus worked auto machine.
If you don't have something positive to say--stay off the thread.
 

sled dog

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Hartdford City, In.
TS, was the thought behind the LPF to try to hold the liners more stable? I maybe remember a Cat mechanic saying the wear on the Cat blocks at the counter bore was the liner rocking side to side a fraction with each piston stroke. At rebuild, deeper counter bore and more shims to square it up again. Am I remembering right?
 

Truck Shop

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TS, was the thought behind the LPF to try to hold the liners more stable? I maybe remember a Cat mechanic saying the wear on the Cat blocks at the counter bore was the liner rocking side to side a fraction with each piston stroke. At rebuild, deeper counter bore and more shims to square it up again. Am I remembering right?
Really Cummins and Cat had the same idea with the shim, really because it's bronze/brass it
is also used as a seal for the liner ledge. Holding the liner tight in the pilot bore area plus the
use of shims from factory really put a end to fretting and counter bore wear. The 444 up came
with LPF and shims, it's fairly rare to see a N14 with head gasket issues. IMO Cummins should
have stuck with the N14, they had the bugs worked out, was a real good engine.
 

Truck Shop

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One thing that is often a thought is putting air to air-CAC on a PT-pressure timed 855.
Not any real advantage, because of the pressure timed system, with a CAC the turbo
lag in some cases causes a loss of horse power.
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A guy that has done extensive dyno testing with a jacketed {coolant cooled} aftercooler
and air to air has found a marked loss of hp. He timed a 625 CPL at a retarded .76 with
20% over fuel and injectors flowed to match pump rail with a N14 3804502 HT60 turbo
and jacketed aftercooler, it produced 520 hp. With air to air it dropped to 495 hp.
Now he was using a aftercooler for the old twin turbo 475, those were a high velocity
aftercooler. He also used a standard aftercooler for a 625 CPL it still produced 510.
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It takes a computer controlled fuel advance/retard to work for air to air on the 855. Fact.
 

DMiller

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Hated cutting blocks when worked at Continental Rebuild, KNEW was last time those blocks could be used as when worn out were Junk. UPF was just becoming a thing as I worked there.
 

Truck Shop

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Because I'm not driving grain truck today {changing a few items on combine and moving equipment
to new patch/plot to harvest dried peas will drive tomorrow}. I had time this morning to test fit liners.
Protrusion specification for lower press fit is .004 to .007, and like I thought all came in at .006 to
.0065 just where those should be. Bugged though-I can't find my accessory drive tool to remove
splined drive hub, put it somewhere I wouldn't forget-now I forgot.
 
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