August
2009
"STORIES"

There seems to be confusion in the trucking industry pertaining to In Chassis Engine Rebuilding vs. Out of Chassis Engine Rebuilding.

This article is going to explain everything that is normally covered during the 2 ways to rebuild a diesel engine in a semi truck. 

In the Chassis means the engine stays bolted to the engine mounts in the chassis of the truck.

  Out of Chassis means the engine is removed from the truck and is rebuilt on an engine stand on the shop floor.

During an in chassis rebuild the engine is dissembled, cleaned and the old parts are inspected to get a better understanding of what wore out and why the engine wore out. 

First we inspect the block for cracks in and around the bolt holes in the head. Next we check for cracks in the upper and lower counter bores.  The upper counter bores are mic'ed to determine if they are level and the liner protrusion (how far the cylinder liner is protruding above the block surface.)  is also checked.  To adjust and set liner protrusion we cut the upper counter bores and install brass or stainless steel shims in place to get just the amount we want.  This is why our rebuild engines very seldom blow head gaskets; we spend a lot of time with the upper counter bores and liner protrusion.  Ignore the factory specs when it comes to liner protrusion, they are way too low and you will blow head gaskets if you go by their specs.

After the upper counter bores are cut you must pressure wash the block with cleaning solvent to remove the cuttings from the counter bores.  Now we start the rebuilding processing by installing the main bearings, liners, piston and connecting rods and rod bearings.  Then comes the head gasket, remanufactured cylinder head, head bolts, performance injectors, camshaft, and rocker arms. The Ported and Jet Hot Coated Exhaust Manifold and performance turbocharger are installed next.  If the front cover of the engine was removed during this in chassis will now be reinstalled and a new crankshaft damper (made in the USA) and a Mercury filled Engine Balancer (made by Balance Masters) will be placed in the end of the crankshaft. 

Replacing Water pumps, oil pump, air compressor, radiator, charge air cooler, front crank seal, and front engine mounts are all optional during an in chassis rebuild. 

  Valve and injectors and now set and adjusted, oil is added and pressurized through the engine. Engine coolant is added along with a new water filter and Fleetgard DCA installed into the radiator to prevent corrosion and electrolysis.  Once the engine is started for the first time we idle it for a couple minutes, check for any miss, and then reset the valves and injectors.

  The valve covers are installed and the engine is painted and the final phase of the in chassis rebuild is the road test.

Out of Chassis Rebuild:  Everything that is done during the in chassis rebuild is done to an engine with the addition of removing the crankshaft from the block, taking the engine to a machine shop and having the crankshaft straightened, polished and magnafluxed for cracks.  Most crankshafts are bent about .020 to .025 thousandths when they have 750,000 or more miles on them.  Then the engine block is hot tanked for cleaning, magnafluxed for cracks. The crankshaft bore is honed straight and the head gasket surface is machined to make it smooth and flat to better hold the head gasket. 

  The cylinder head is also hot tanked, magnafluxed, resurfaced, and new valves, valve springs with 10 psi more pressure than a stock spring, new retainers, keepers, and valve guides are installed.  The cylinder head we use does cost about $300.00 more than a factory Reman Head however all of the parts are new where as the factory head reuses many parts that are at the minimal spec such as valve guides, valve stems and valve springs.

Connecting rods are magnafluxed for cracks, reconditioned on the crankshaft end, new bushings in the wrist pin bore, then the distance from the center of the crank end to the center of the wrist pin bore is mic’ed and the wrist pin bore is machined to hold the center line distance.   Also the connecting rod is balanced and checked for twisting.

Something to keep in mind, if your transmission has about 1 million miles on it you just might want to have it rebuild while its out of the truck and have the flywheel resurfaced and a new clutch installed.  With today’s labor rated is much more economical to do it now and only pay for labor once.

Now the components are returned to our shop and the engine is assembled.  With the straightened crankshaft installed into the honed block all it takes is one hand to turn the 400-pound crankshaft.  During the assembly process all of the components are checked, rebuilt or replaced.  New engine mounts; radiator mounts and charge air cooler mounts are installed.

We also send the radiator to our rad shop to be checked and cleaned or have the radiator core replaced with our performance rad core.  Our core has 364 dimpled tubes for the Kenworth or Peterbilt vs. 170 to 234 straight tubes that the OEM's use.

As you can see, you can spend a lot of money on an out of chassis rebuild; however you are good for another million miles of high performance trucking, and you will have a smile on your face every time you look at your truck.   Your decision is this: do you want to keep your truck for several more years or buy the new junk our OEM's have been forced to build by our own government!

Written by; Bruce C. Mallinson; Pittsburgh Power Inc.; 3600 S. Noah Dr.; Saxonburg, Pa. 16056. Phone 724-36-4080