Engine rebuilds come in many different varieties.

Take a look at the vast array of engine rebuild kits available through Summit Racing, and you’ll see the contents vary from kit to kit. Some include things like gaskets, bearings, and piston rings. Others are more comprehensive and also come with pistons, timing set, and a camshaft. The bottom line is, the extent of the rebuild — and the rebuild kit required —depends on the condition of the engine internals and your plans for the engine. For example, if you’re plucking a used engine from the junkyard and plan to use it for a performance build-up, you might consider a complete rebuild with machine work. On the other hand, if your existing engine is encountering problems, you may only need a few pieces to get it running right again.

The key is understanding the problem areas and how to fix them.

Some obvious signs of a rebuild candidate are power loss, poor fuel mileage, and excessive oil consumption. Fortunately, there are a few ways to narrow down where your problem(s) lies without doing a complete teardown of your engine. You may need a massive rebuild. You may need to replace one set of components. Here are some ways to find out:

Check Your Oil — and Oil Pressure

Excessive oil consumption and low oil pressure are not only a signs of trouble, they’re also hints as to where the problem is located. These problems are typically linked to the clearances between the parts within your engine. As the parts wear, the clearances increase, allowing oil to escape into your engine where it is burned off. This typically shows up as a bluish smoke emanating from your exhaust.

The usual suspects for excessive oil consumption and low oil pressure include broken piston rings, worn valve guides, and worn bearings.

Listen to Your Engine

Those odd sounds coming from your engine can foretell problems.

More importantly for you, they can provide clues as to where the problems exist. For example, a broken piston ring will make a rattling noise. Excessive clearance between the piston and cylinder bore will sound more like a knock. A chatter at half engine speed is the telltale sign of valvetrain-related issues.

Grab an automotive stethoscope and get in tune with the health of your engine.

See our original post on engine noise for more information.


Look at Your Spark Plugs

Your spark plugs say a lot about your engine’s performance.

Reading your spark plugs is a good way to tune your engine, adjust the air/fuel mixture, and check for detonation. And if the plugs have wet black deposits on the threaded portion and plug insulator, they may be telling you it’s time to replace worn out piston rings or intake valve guides. In this instance, the wet deposits are caused by oil entering the combustion chamber.


Check the Compression

Along with oil consumption, loss of compression is a top indicator of internal engine problems. This could include a blown head gasket, worn pistons rings, worn cylinder bore, cracked cylinder head, or burnt exhaust valves.

So how do you narrow it down further?

There are a couple of ways:

Leakdown-Tester-05-1600x1200Compression Testing: Using a compression gauge, you can do comparative testing of an engine’s cylinders. The pressures between the cylinders shouldn’t vary greatly. For example, in HP Books’ How to Rebuild Small Block Ford Engines, author Tom Monroe suggests the lowest pressure shouldn’t vary from the highest pressure among the cylinders by more than 75 percent. If pressure in one or more of the cylinders differs by more, try adding a tablespoon of oil to the bad cylinders. If this causes the pressure to increase, the rings and bore are at fault, and you’ll need to rebuild.

Leakdown Testing: A leakdown tester is a more comprehensive way to test your engine’s condition. Typically, if a leakdown tester finds an engine leaks 20 percent of the test pressure (applied by leakdown tester), the problem is a broken piston ring, burnt valve, blown head gasket, or cracked cylinder head or cylinder wall.

Examine Your Coolant

If you suspect a blown head gasket, examine your coolant.

If there is an unusual amount of coolant loss from your radiator, it’s a sign that cylinder pressure is leaking into your cooling system. Carefully remove the radiator cap and look at the coolant surface with the radiator warmed up. If you see bubbles, that means cylinder pressure is leaking into your cooling system. If you detect a gasoline or exhaust smell within the coolant, you probably have a blown head gasket on your hands. There are also Combustion Leak Detection kits available to aid in realizing that hard-to-find blown head gasket!



Look at Your Valves

If you’ve found compression loss and eliminated your head gaskets and pistons rings as the cause, turn your attention to your valves. Burnt exhaust valves or sticky valves (won’t close) will prevent a combustion chamber from fully sealing, causing a loss in compression. Remove your valve covers and check to see if the valves are fully closed using calipers or dial indicator. If a fully closed valve leaks, it’s probably burned.



Perform a Cam Exam

Some rebuild kits also include a performance camshaft. This is because camshaft lobes wear over time, necessitating the need for a new camshaft. While you’re inspecting your engine, you may also want to check for camshaft lobe wear by double checking the lifts of each individual lobe. Camshafts usually experience wear on one lobe at a time, but you should replace the camshaft and lifters even if the wear is confined to a single lobe.

If you find cam lobe wear but haven’t noticed excessive oil consumption or compression loss, you can probably just replace your camshaft. However, if your engine is burning oil and compression is low on some cylinders, you’ll likely need a complete rebuild.

Using this guide, you may replace one or two components (ring and valve job) or do a complete rebuild with one of the many engine rebuild kits available. In our next installment, we’ll look at some tips for rebuilding your engine and provide some options for your project.

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Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.