Here’s What You Need to Know About Engine Overhauling

Engine overhauling is a concept of tuning up an engine by disassembling it, testing its components and replacing the defected ones. The purpose behind all this process is to revive the performance of the engine and prolong its life. Here’s what you need to know about engine overhauling. Engine overhauling can be basically done in ways:

  • In-chassis Rebuild
  • Out-of chassis Rebuild

In-chassis Rebuild:

The easiest way to rebuild and revive your engine’s performance is to conduct an in-chassis rebuild. This is basically done without removing the engine from the car. All the defected parts of the engine are pulled out for a minor overhaul. An In-chassis rebuilt may generally consist of replacing cylinder liners, piston rings, crankshaft bearings, valve stem seals, oil pump, and head gasket. Repairing or replacing these components of the engine might help in reviving the engine’s performance to a great extent.

  • Another sub-category of In-chassis rebuilt is ‘Major Overhauling’ also known as ‘top overhaul’. The major overhauling technique covers inspection and replacement of spark plugs, cylinder heads and vales. A top overhauls proceeds with a compression test. It is important to mention that piston rings are not generally replaced.

Out-of-chassis Rebuild:

The major concept of engine overhauling revolves around Out-of-chassis rebuild. The engine is detached from the car, unbolted totally and thoroughly cleaned and inspected. This overhauling technique involves replacing all the major components of engine with new factory stock components. Other parts such as block casting, head casting, crankshaft, conrods, flywheels and camshafts can also be repaired if they aren’t totally tattered. For a locally manufactured car, an Out-of-chassis rebuild might save you some extra bucks as compared to buying a completely new engine.

Engine overhauling becomes necessary if your engine starts to fail. Overhauling of engine may help in reviving the performance of the vehicle but it may cause some reliability issues in the long run. Sometimes, engine swapping can be a better option as compared to overhauling. In case, you are using an imported car and its engine is excessively worn out, engine swapping can be much more economical as compared to out-of-chassis rebuild.

List of components:

You may think of engine overhaul as a replacement of piston rings and bearings. But here’s a complete list of components that need to be inspected, cleaned, repaired or replaced during an engine overhaul.

• Cylinder heads
• Cylinder valves
• Exhaust riser or elbows
• Sea water pump
• Circulating pump
• Oil cooler
• Heat exchanger
• Thermostats
• Senders & sensors
• Drive plate adaptor
• Crankshaft seals
• Injection pump
• Injectors
• Fuel cooler
• Turbo chargers (if present)
• Blowers
• Intercooler (if present)

Certain bolts and nuts may also be replaced due to rust or corrosion. Once the engine is overhauled, it may later cause certain problems like fuel efficiency, cabin noise, vibration on idling and etc. Once you decide to get an overhauling job done, make sure you go to a qualified and expert mechanic or you will end up losing your money against a deadly engine.


Shaf Younus

I'm an Auto Enthusiast, a Computer Science Graduate and above all, Citizen of Pakistan.

Notable Replies

  1. Rugal says:

    What I need to know about engine overhauling cannot be learnt from this article. There is also the atrocious spelling. Also, please note that the following items are usually found in marine outboard motors, not car engines.

    • Exhaust riser or elbows - This is something that prevents water from getting into the engine via the exhaust. Also helps keeping the exhaust system on an outboard cool.
    • Sea water pump - Well obvious, I guess. What car engine has a sea water pump?
    • Drive plate adaptor - Again something that is used to mate an engine to a marine transmission system (Forward, reverse, neutral and usually that's it) since most of them come separately from different manufacturers unlike car engines.

    The following items are usually part of performance engines, not your regular Mehran.

    • Oil cooler - Not found in stock liquid cooled engines, only high performance modded cars or air / oil cooled engines like those in old Porsches or VW Beetles.
    • Fuel cooler - A performance modification for cooling the fuel so that the density of the fuel / air mixture improves. Better density = more power.
    • Blowers - One presumes the author means superchargers. Again, noticeably a performance item as opposed to an actual stock car component working on the same forced induction principles as that of a turbo. Unlike turbos that use exhaust gases, superchargers usually work with belts or chains connecting their turbines to the engine crankshaft.

    Finally, some words that are still bothering me...

    • Senders & sensors - What the hell is a sender?
    "Once you decide to get an overhauling job done, make sure you go to a qualified and expert mechanic or you will end up losing your money against a deadly engine". - A what engine? Deadly? Sounds like something out of the DC Universe to me.

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