It’s every owner-operator and fleet manager’s worst nightmare. Your truck has been running rough, losing coolant and blowing black smoke. You bring it to your local heavy duty repair shop and after diagnosis, they tell you your engine is tired and you need an engine rebuild. For any company, this is a complex and costly repair that nobody wants to deal with. There are two types of engine rebuilds that can be done, but they are both quite expensive. The first is an “In frame”. This is usually done as preventative maintenance to restore engines back to proper working order. The second is an out of frame overhaul. This is done when an integral component has failed, resulting in damage or when more in-depth work is required.

In-frame engine rebuild

An “in-frame” enginerebuild is the process of rebuilding the engine without removing the engine block from the frame. As stated previously, this is usually done as a preventative measure when the engine has started to show signs of age. Symptoms such as excessive blowby (exhaust gases seeping past the piston rings into the block), poor fuel economy and burning of coolant are all good indicators that it is time to have an in-frame engine rebuild completed. The in-frame engine rebuild process begins with engine disassembly and inspection of major internal components. The pistons, piston rings and cylinder sleeves will be removed and replaced with new parts. The oil pan will also be removed and crankshaft and main bearings will be replaced (this can be done without removing the crankshaft from the block). When it comes time for reassembly, all necessary O-rings and gaskets that were removed will be replaced with new ones to prevent leaks when the engine gets running again. The engine rebuild process will also include a new cylinder head gasket and replacement of cylinder head. Throughout the entire process, the technician will take note of any other components that potentially require replacing. Any extra parts or labour required will be discussed further with the customer before being carried out. Finally, once the engine rebuild has been completed, the engine will receive new fluids and filters to ensure maximum cleanliness of fuel and lubricants upon initial start-up.

Out-of-frame overhaul

An out-of-frame engine rebuild or “overhaul” is a much more extensive and a much less desirable option as it’s more labour intensive and costs more than an in-frame. An out-of-frame is carried out when one of the main engine components such as a piston rod, or the crankshaft has failed, resulting in damage to the engine. An out-of-frame overhaul may also be necessary on more extreme high mileage engines where the cylinder block is warped which will require

machine work to be done in order to get everything fitting together again. The process for an overhaul includes all the steps of an in-frame, however, there are some extra steps taken in the teardown process. The crankshaft will be removed from the block and measured for in spec clearances. If the crankshaft is found to be out of spec then it will require replacing. Another step in the overhaul process is to check the mating surfaces of the cylinder head and engine block. If either of these surfaces is found to be warped, then it will require machine work to true these two surfaces up in order to get them fitting flush again.

Break-in procedure after engine rebuild

If your engine received either an in-frame engine rebuild or a complete overhaul, both processes require a break-in period when the engine is returned to service. The engine will require a break-in period in order to seat the new piston rings against the cylinder sleeves.

There are two main ways to break-in an engine. The first is rather simplistic and involves pulling a trailer loaded with the maximum weight allowable for the truck. This load should be pulled at a high gear for a distance of 300-500km. It is important to avoid high RPM light load conditions during the break-in period. The engine needs to work under load in order to properly seat the piston rings.

The second, more ideal option is to run the engine on a dynamometer. Running the new engine on a dynamometer allows for the break-in procedure to be carried out in a more controlled environment where the engine load and rpm can be carefully monitored and adjusted as necessary. This will ensure that the break-in procedure is done properly and that the new engine will be running at peak efficiency when it hits the road. It is important to note that failure to break-in an engine properly immediately after an engine rebuild may result in low power, poor fuel economy and excessive oil consumption. To put it short, if you don’t properly break-in the engine, you may be worse off than before you started.


Needing to have your diesel engine rebuilt is one of the biggest and most complex repairs that you may encounter while you own your truck. It may seem tempting to throw in the towel and trade your rig in for something new. Although this is sometimes an option, it doesn’t have to be the only answer.

At Overdrive Heavy Duty,our technicians have the skills and knowledge required to carry out any extensive engine repairs required to reduce your downtime and get you moving again. We deal with all major brands including CAT, Cummins, Detroit Diesel, Mack, Paccar and International. If you think you may require an engine rebuild, check out our blog, 5 signs you need an engine rebuild, or book an appointment with one of our specialists today!