What Exactly Is An Engine Overhaul?

I have heard it before and always wondered exactly what it is. When is an engine overhaul necessary? What does a complete engine overhaul consist of? Thank you.

11 Answers

  • Hruth
    Lv 5
    1 decade ago
    Favorite Answer

    An engine overhaul is necessary once the engine is worn out i.e. high mileage, blowing blue smoke, rattling and rough.

    There are different ways of overhauling an engine. Most workshops do what is called an in-chassis rebuild. This is where you don't remove the engine from the car, you just pull what you need to do the job off it and do a minor overhaul - replace the cylinder liners, pistons (if they need it), piston rings, replace the big end and crankshaft bearings, lap the valves in and replace the valve stem seals, strip and check the oil pump, replace the gaskets and seals Just what is needed to be done to bring the engine back to factory specification and performance.

    A major overhaul or out-of chassis rebuild is much more thorough. The engine is removed from the car (obviously) and totally stripped down - every nut and bolt is removed, cleaned, checked. Most moving parts are replaced with brand new factory stock parts - often the only original parts of an engine that has been MO'ed are the block casting, the head casting, the crankshaft, conrods, flywheel and camshaft. If any of those aren't in serviceable condition they they get switched out too. And the motor gets a fresh paint job. An MO is much more expensive, but it's like you get a brand new engine back, while still usually costing less than actually buying a brand new engine.

    Then there is the process of 'blueprinting' an engine. This is an MO, but much more detailed. There are manufacturing tolerances that mean there can be slight differences between two parts that essentially are the same. They are the same, only not quite. Blueprinting fixes that. All the parts that are supposed to be the same, are exactly the same. Conrods and pistons are weight matched and balanced. The crankshaft is also perfectly balanced, instead of "close enough is good enough". When you replace bearings with stock parts, once again there are manufacturing tolerances. Some crankshaft and camshaft bearing journals are ever so slightly bigger or smaller than others and with stock bearings this causes extra friction and slight loss of power. When you blueprint an engine, you custom fit bearings to each individual journal.

    To put it simply, if you had two brand new engines, one factory stock, right off the test dyno at the assembly plant and just been finshed 'running in', and one that had been "blueprinted" (but still stock, no aftermarket performance parts) by a performance workshop, and compared the two, the blueprinted motor would not only start easier, run quieter and smoother, but also use slightly less fuel, and make a little more horsepower. It would also be more responsive and rev quicker.

    Source(s): I am a qualified diesel technician.
  • 4 years ago

    Engine Overhaul

  • 1 decade ago

    An overhaul consists of honing the cylinder bores is possible. New piston rings. If not, a re-bore. That would require new pistons and rings. New cam bearings, new main bearings, new rod bearings. A valve job. All new gaskets, timing chain, freeze plugs, and oil seals.

    It would be a good time for performance improvements if you are going this far. This would include a new cam and polishing the crankshaft and balancing the engine. With a new cam you will need new lifters and valve springs. New aluminum cylinder heads.

    If you tear it down and reassemble it yourself and have the machine work done at a good shop you can get away under $2000. If you want to improve the performance it will cost upwards to $5000. More to have all the work done.

    Some crate engines are a good deal as they come complete and all new.

    But doing it yourself is satisfying.

  • ilsa
    Lv 4
    4 years ago

    Define Overhaul

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  • 6 years ago

    Since overhauls fall into the four basic categories, then what are the "high priced" engine companies charging you for? Here are a few of the more popular advertising claims being made today. What do you think?

    Increased Reliability?

    There are many claims being made about special “techniques” and exotic “procedures” that supposedly increase the reliability of a given companies overhauled engines. These claims are accompanied by high overhaul prices that are meant to cover the “cost” of putting this special technology into your engine. Now, stop and ask yourself something: If these companies really DID have a way to increase the reliability of an aircraft engine, wouldn’t the manufacturer be doing it and recommending it today? Of course they would.

    Modern aircraft engines are, by design, very reliable. A big part of this reliability is due to the fact that engine manufacturers have set standards for the parts used in the engines, the acceptable condition of those parts and the method used to assemble those parts into a complete engine. Strictly following the manufacturers “new engine limits” guidelines at overhaul is the very best way to insure your engine will offer the same level of reliability it did the day it was brand new.

    Increased Performance?

    We will be the first to tell you there are specialty shops that can extract considerably more horsepower than is offered in a stock aircraft engine. High compression pistons, special profile camshafts and custom machine work in the combustion chamber and valve areas can produce significant horsepower gains. Some of the hottest experimental aircraft flying today make use of these modified engines to achieve their incredible performance. The key phrase here is experimental aircraft.

    The engine manufacturers and the FAA have set rigid guidelines concerning modifications that can be made to a certified engine part. A few overhaul shops have elected to explore the “gray area” of these safety guidelines. Unless you fly an experimental aircraft, you should give serious thought to the reliability and liability issues of installing an engine in your aircraft that may have received modifications that could adversely affect its FAA certification.

    Increased “Smoothness”?

    One of the latest fads is “precision, dynamic engine balancing” for increased smoothness. We agree that reducing the vibration levels in any aircraft is desirable for numerous reasons. Increased passenger comfort, reduced airframe fatigue, longer avionics life.

    The engine manufacturers also acknowledge this by establishing the guidelines for the balance of their engines' rotating components. If the engine overhauler follows these guidelines, which take into account the engine's total rotating mass and relatively low operating RPM, your engine will run smoothly. The one thing you can do to significantly reduce vibration is insure the correct balance of the engine/propeller combination once they are installed back into your aircraft. So before you pay to have your engine “dynamically balanced” during overhaul, consider using that money to have your propeller/engine combination dynamically balanced as needed. You, your aircraft and engine will be much happier with the result.

    The Bottom Line

    After you cut through the “techno-babble,” fads, and marketing hype, one simple fact remains:

    The best way to insure the same reliability, performance and longevity the manufacturer designed into your engine is to choose an overhaul facility that follows the guidelines set forth by the engine manufacturer and the FAA in order to comply with a “new limit overhaul.”

  • MSS
    Lv 6
    5 years ago

    I agree with Hruth, but want to add, you should only do it if a qualified tech told you to do it. Some vehicles may have a 15-20 year engine that works perfectly fine without an overhaul.

  • 4 years ago

    my diesel car mile leage is over 200,000 km. does it need overhaul?

  • 5 years ago

    Hi there @hruth

    I am looking at purchasing a VW golf 1.9 tdi with 192000Kms on the clock. The seller mentioned the engine was done over (mentioned barrings replaced etc). will be test driving the car on the weekend so do you have any input on what I should be paying attention to when test driving the car.

    Is it ok to purchase a car with the engine done over? what questions would you be asking if you were me?

    Your input will be valuable.


  • Anonymous
    4 years ago

    This question is worth people's attention

  • 6 years ago

    its unikl mfi

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