Overhaul

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When overhauling the engine due to low compression or excessive blowby, new piston rings are installed to bring it back to specification. Normally a re-bore and new pistons are not required -- it is not part of an overhaul. All other parts are inspected and measured (but only replaced if damaged or out-of-specification). To finish the overhaul, new gaskets are installed.

Overview

If your engine is requiring an overhaul, consider saving time and money by purchasing a good used engine. Often one can be found on trader sites or by asking in the Classifieds. This is also a good time to upgrade to an A14 or A15 engine.

Also see:
*  Engine Overhaul & Service Data (in Japanese)

• If you are only trying to fix oil leaks, a re-gasketting is called for and an overhaul is not needed

• To check if the engine compression is defective, see Compression Test

• If the engine has a rod knock or main bearing knock it probably needs and overhaul. But you may only need to replace the bearings if the engine is in otherwise good shape.

• If the engine sometimes doesn't run right, don't start with an overhaul but instead troubleshoot it. It may an ignition or carburation issue -- which an overhaul won't fix

Engine overhaul includes:

* New piston rings
* New Rod bearings and Main bearings (if required) 
* New gaskets
* Replacement of any out-of-spec parts

Parts that are unlikely to last another 100,000 miles/160,000km are often replaced even if still in working good condition, including the Water pump. Bolt-on Accessories such as Smog Pump and alternator are not part of an engine overhaul.

Not normally part of an overhaul unless out-of-spec or damaged:

* Cylinder Block
* Cam bearings
* Camshaft
* Head milling
* Bolts, including Rod bolts and Head Bolts
* Carburetor, Distributor or Alternator

Installation

When installing an overhauled engine, it is customary to replace these parts:

• Tune-up#Engine_TUNE-UP including new tune-up parts: Spark Plugs, Distributor Cap, Rotor and Points and new PCV Valve
• Oil and Oil filter change

Overhaul vs Re-manufacture

A re-manufactured engine is a used engine restored to as-new condition. As such, ALL service parts are replaced even if they are working fine or within factory specification.

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* Pistons
* Piston rings
* Bearings
** Main Bearings
** Rod Bearings
** Cam bearings
* Camshaft and Lifters
* Cylinder Head:
** Valve springs
** Rocker arms
* Timing Chain and tensioner 
* Gasket
* Oil pump
* Welch Plugs
* Acessories including:
** water pump

Non-service Parts

Non-service parts do not require periodic service, last indefinitely, and are not normally replaced unless damaged. They should of course be inspected at overhaul or remanufacture time:

* Pushrods inspected for straightness
* Bolts including
** Head Bolts
** Rod Bolts
** Main Bearing Cap bolts