Semi Truck Engine Overhaul: Inside a Recent Job

This is a recent engine overhaul from our shop at 700 Trumpet Pk Dr in Zion, IL. The engine is an inline-six heavy-duty diesel. The head is off, and the cylinder liners and connecting rods are out of the block for inspection and replacement.

Signs Your Engine May Need an Overhaul

An overhaul is a big job, so it should be backed by a clear diagnosis. These are the symptoms that usually lead there:

• Heavy blow-by: a lot of smoke or pressure coming out of the crankcase breather
• Oil consumption that keeps climbing between oil changes
• Low power and low compression on one or more cylinders
• Coolant in the oil, or oil in the coolant
• Knocking from the bottom end of the engine
• Metal in the oil or on the drain plug

Some of these can also come from cheaper problems, such as a turbo, an injector, an oil cooler or a head gasket. That's why we diagnose first. See engine repair & diagnostics.

In-Frame vs Out-of-Frame Overhaul

In-frame: the engine stays in the truck. Liners, pistons, rings and bearings are replaced in place. It usually costs less and takes less time, and it fits engines where the crankshaft and block are in good shape.

Out-of-frame: the engine comes out of the truck. This gives full access to the crankshaft, camshaft and block. It's the better choice when there is bottom-end damage, a spun bearing, or when you want the most complete rebuild.

What an Overhaul Typically Includes

• Cylinder liners, pistons and rings
• Connecting rod and main bearings
• Gaskets and seals
• Cylinder head inspection and valve work
• Related parts as needed: injectors, oil cooler, water pump, turbo

The final list depends on what we find after teardown. We show you the worn parts and confirm the quote before we order anything.

Overhaul or Replacement Engine?

It depends on the condition of the block and crankshaft, the age and value of the truck, and how long you plan to keep it. When we have the engine open, we can tell you which option makes more sense for your truck.