Humbled
The lateness of the hour (to say nohing of the subject matter's technicality) preclude much comment from me on the following message. I am humbled by the anonymous author's camaraderie and his willingness to help others, evident in these pages and at this forum among those who share and love the open road. And to again voice my appreciation for his and their generous spirit. Have a terrific Sunday. RD
Hi Roger, I would not be one to dispute another's judgment that makes
a living performing a given service like this.
Theoretically an engine exists as a design "blueprint" before
manufacturing. This blueprint is put into production and by the time
the engine is complete, (cylinder block in this case) it is subject to
manufacturing tolerances. Although slight, the main saddles machined
into the block can be just a bit out of perfect but well within
manufacturing tolerances and allowances. This can be bettered or
brought closer to exact as far as alignment with align honing the
saddles, or bores supporting the main bearings and thus the
crankshaft. Think of it like this: When an engine is running there is
a lot of downward force exerted upon the piston crown from ignition of
the fuel. This force is transferred into the connecting rod, bearings,
and the crankshaft causing minute deflection of the the shaft. This
force eventually causes slight wear through the main saddles of the
block. Again this is slight. Now imagine a rod bearing going bad. The
bearing clearance opens up, the force from ignition is now applied
through a larger opening "slamming" the rod against the crankshaft
harder and possibly deflecting, or distorting the bore. Align honing
will correct this if slight. Again this is hypothetical. If the
bearing bore is distorted above the point that a competent shop does
not think the bores can be realigned by shaving the bearing caps,
boring them back round, then honed to perfection, the block must be
replaced. To take this further: Imagine the lower end of the cylinder
block with the bearing caps installed and torqued properly. The
imaginary centerline of the bearing saddles are not in perfect
alignment with each other. If a round bar a couple of thousandths
smaller in diameter that the bore of the bearing saddles is placed in
the bearing bores, the main bearing caps torqued correctly, and the
bar rotated, there will be slight "drag" due to the bearing bores
being just a bit off due to manufacturing tolerances. This figure is
close enough to work, but can be improved upon.
Basicall what this does is "true" the bearing saddles into alignment
with each other. This allows the crankshaft to rotate more freely
within the bearings. I feel any reduction in friction is a plus.
I've never done a large truck diesel engine myself but have been
around several "pullers" the rely on expert machine work to allow
their engines to run high rpm's under pull and stay together. I have
built several race car engines, (gasoline), and pickup diesels, and
always have the blocks decked, squared, and align honed. The rotating
assemblies are then weight matched to less than one gram each. The
term decking, and squaring refers to having the centerline of the main
bearing saddles, and the cylinder head mounting surface brough to
blueprint specification in height. This is also referred to as
"blueprinting" and engine. The operation removes the manufacturing
tolerances, and brings the engine as close to design criteria as
possible.
The last 275hp 8.3 Cummins diesel I rebuilt cost $750.00 for the
balancing and block work mentioned earlier. The engine runs much
smoother than the original configuration. I would equate it to almost
a 454 Chevrolet engine at idle.
I'm surprised this service does not appear to be performed in the area
your truck is located in. It is quite common up here in central
***** and *****. If your engine did not have problems and just
needs "freshening up", it could be done without. A 3406 engine is
smooth in design operation, but I've seen them balanced and a glass of
water would sit on the cam cover atop the engine, not walking off from
vibration at idle.