Building Small-Block Fords: Why Engines Wear Out

Automobile engines have a tough job to do. For the most part, they do it well for many years and thousands of miles reliably. Trouble abounds when we don’t take care of them, or when we put them together improperly. When we do take good care of them, engines can last between 100,000 and 200,000 miles. Depending on how much you drive, that’s about five to ten years of use. With a new timing set and oil pump at 120,000 to 150,000 miles, along with regular oil and filter service every 3,000 to 5,000 miles, you might see in excess of 250,000 miles from your engine.

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The greatest rider you can put on your engine’s life insurance policy is regularly-scheduled oil and filter changes using Mobil 1 synthetic engine oil and a Wix or Motorcraft oil filter. With clean oil in the pan, you’re assured a solid barrier between all moving parts inside your small-block. And when you use synthetic engine oil, it stays on moving parts, even when an engine sits for days. This affords you good protection during start-up.

Another important point is regular cooling-system service. The wise enthusiast will flush and service the cooling system every spring or fall. If it’s hard to remember to do that, opt for cooling system service every two years. You can get away with some degree of cooling system neglect when you’re running iron cylinder heads. Whenever you step up to aluminum heads, you are mixing dissimilar metals that don’t like each other. Aluminum particles wind up attached to iron castings – and vice versa. The result is corrosion. This is one reason why we don’t see copper and brass radiators in new cars anymore. Other reasons include weight and cost; aluminum radiators with plastic tanks are lighter and cheaper. So why do engines wear out?

Engines wear out mostly due to dirty oil, poor filtration, poor tuning, neglect, and even improper assembly to begin with. If an engine is built with poor dynamic balancing, vibration will shorten its life. If main and rod bearing side clearances are too tight, expect a short trip. Pistonto-cylinder-wall clearances are yet another reason. This is why checking and rechecking clearances during the build up is so important.

Valvetrain issues are likely the greatest cause of engine failure. This encompasses a lot of items – burned valves, worn stems and guides, excessive rockerarm wear, wiped cam lobes, worn lifters, and timing chain and gear failure. The greatest area of neglect we see time and time again is the timing set. When our small-block Fords were young, most of them had nylon-coated aluminum timing gears. Ford did this to help make the timing set run quieter. We have replaced an untold numbers of nylon and aluminum gears with steel gears over the past 40 years. I’ve never been able to hear the difference in the steel gear or chain.

Many people tend to whistle in the dark when it comes to timing sets. They’re like that elephant in the living room that no one wants to talk about. Timing sets are a pain in the neck to replace, which is why we continue to put replacement off. And then they fail, often with catastrophic results. With the nylon-coated aluminum cam gears, both aluminum and nylon crumble and flow into the oil pan. When they do, they wind up in the oil pump and bearings. Finally, main, rod, and cam bearings are damaged from the debris.

Sometimes, timing sets are replaced with no regard for the debris that got into the oil pan. We press them back into service, with serious fluctuations in oil pressure and volume. If we’re lucky, we’ll get an “oil” or “check engine” light and have sense enough to pull the oil pan and clean out the debris. Some people will just push the engine until it fails.

Engines also fail from poor tuning technique – too much timing or too little. Too much timing hurts the engine by changing the way the air/fuel mix ignites in the chamber. The more we advance the timing, the longer the flame travel and the higher the combustion temperatures. With this advance in ignition timing, we create hot spots – additional ignition sources that create colliding flame fronts and shock waves across the top of the piston. This is known as detonation, or the “pinging” we hear in spark knock under hard acceleration.

Advancing the timing in healthy increments helps us make power. However, too much timing (too much advance) can do permanent engine damage. Late ignition timing won’t hurt the engine as badly as too much advance. However, late ignition timing sends high combustion temperatures teaming toward exhaust stroke. This causes exhaust valves and headers to run considerably hotter. It also robs us of power.

 

 

An extremely lean fuel mixture that comes from improper carburetor jetting or a worn-out fuel pump can cause serious engine damage. If your engine has electronic fuel injection, faulty sensors will create all kinds of grief. Faulty oxygen sensors can cause extremes in fuel mixture – either overly rich or extremely lean. Coolant temperature, manifold air pressure, throttle position, inlet air temperature, and mass-air sensors can become defective, adversely affecting fuel mixture and spark curves.

There are engine failure issues that aren’t as obvious as some of the items we’ve covered here. The use of incorrect parts is one of them. Our 289 had two different valvestem lengths, which adversely affected rocker-arm geometry on the left bank. This could have caused rocker-arm failure due to stress. A failing rocker arm can cause a pushrod to come right through the valve cover. It can also cause valvespring retainer failure, which causes a valve to drop into the cylinder.

Using incorrect valvesprings can cause engine failure or abnormal wear issues. Valvesprings that are too stiff can wear cam lobes and cause excessive valvestem wear. Valvesprings that are too soft can cause valve float at high revs, which can lead to engine failure. Valve float refers to runaway valves that don’t seat at high revs because the valve springs aren’t stiff enough to snap them closed. When valves float (stay open) at high revs, we run the risk of valve-to-piston contact, which virtually guarantees us total engine destruction. This is certainly more possible if we’re running a high-lift camshaft where valve-to-piston clearances aren’t much to begin with.

Using a double-roller timing chain without considering the clearance between your oil slinger, timing chain, and timing cover can cause metal trash to enter the oil, eating the main, rod, and cam bearings alive. Metal gets into the oil when the oil slinger lip rubs against the dual-roller timing chain. You can flatten the oil slinger gently with a hammer, which moves the lip away from the chain. This is best performed by using a block of wood between the hammer and oil slinger.

An oil pump driveshaft with worn ends can slip, twist, and fail, rendering the oil pump useless. When the oil pump brakes down, the engine brakes down – unless you’re quick with the ignition switch.

Using rail-style rocker arms on a 1962 through early 1966 small-block Ford is a mistake we see from time to time by technicians who are not familiar with these engines. The side rails press on the valvespring retainers, especially if you use a high-lift camshaft. The repeated pressure on the retainer leads to keeper failure – and catastrophic engine damage when stray valves fall into cylinders.

Written by George Reid and Republished with Permission of CarTech Inc