High-Performance Engine Failure Analysis

#1- Pistons that look like this after you pop them out of the cylinders indicate over-enthusiastic spark timing, an excessively lean air/fuel mixture or both. The "black death" on the skirts is the result of severe detonation that blasted material from the dome. This abrasive material, a mixture of aluminum and carbon, worked its way past the rings and wiped out the skirt. It didn’t do much for the cylinder walls either.

#2,2a - A piston that looks like this indicates a properly built and well-maintained engine. This one, from a Limited Late Model, was used for a complete season and shows normal wear and is reusable. Some engine builders get up to four seasons of racing from a single set of pistons in some applications. While pistons from some engines will have carbon completely covering the domes, others will have a ring around the outside, especially along a crescent at the furthest point from the spark plug where no deposits are evident. Both conditions are normal, depending upon combustion chamber shape, deck clearance and dome configuration.

#3 - This set of rod bearings, installed on journal number one, shows a bit of wear, but the wear pattern is normal. There’s no evidence of lubrication, machining or assembly problems.

#4 - Believe it or not, these rod bearings are from the same engine as shown in photo number three. Installed on journal number three, they show more scuffing and abrasion than their counterparts in the previous photo. That’s because they were closer to a crack in the number four main journal.

#5 - The wear pattern on these main bearings is normal for an engine lubricated by a wet sump oiling system - except for scuffing and scratching caused by dirt. Mr. Clean may be stronger than dirt, but engine bearings aren’t. To prevent dirt from entering the lubrication system, all valve cover vents or fill holes should be fitted with a filter or tightly capped. Obviously, popping the valve covers off in the pits (especially at a dirt track) isn’t a good idea. If it’s necessary to remove the covers, only one should be removed at a time.

#6 - These bearings look considerably better than the ones in photo number five, but there’s still evidence of problems. They were removed from an engine that had run normally in seven races, but during the last two events, the driver noticed the oil temperature was higher than normal. After tearing the engine down and inspecting the bearings, the engine builder magnafluxed the crankshaft and found a crack at the number four main journal. The crankshaft started life as a good piece, machined from a 5140 forging. However, it had been damaged previously and repaired. Even though it had been re-heat treated after the repair, the area was still obviously weak. In this instance, the alert driver saved himself from complete engine destruction. Had he ignored the elevated oil temperature, there’s a good chance the crank would have broken during a race, and taken the block, rods and heads with it.

#7 - This cam, which served its owner faithfully for two seasons, has lobes that show a normal wear pattern. Notice that it’s getting a bit wide across the nose (see arrow), indicating that replacement time has arrived. Pitting on the nose is the result of poor maintenance - the owner didn’t change oil regularly.

#8 - After this cam had been in use for only two weeks, the driver noticed that the engine was down on power - for good reason, the lobes were well on their way to going flat. Accelerated wear is most commonly caused by improper heat treating, excessive valve spring pressure or valve spring coil bind. If a camshaft is properly heat treated and broken in properly, accelerated wear problems can be avoided by matching valve springs to camshaft profile and carefully checking spring set up.

#9 - It’s a little difficult to see in this black and white photo, but the big end of this connecting rod has been turned blue by excessive heat caused by a spun bearing. The bearing went for a spin because a faulty distributor caused a shift in ignition timing. Purposely getting over-enthusiastic with spark advance can cause similar results.

#10 - Need proof that one picture is worth a thousand words? Here it is. The driver noticed a miss during a qualifying lap but decided to race anyway. Sometime after the green flag dropped, so did a couple of valves. The cause? The same broken valve spring that caused the miss during qualifying. Racers and street performance enthusiasts often cause problems for themselves because they don’t pay enough attention to valve springs. They have to be installed properly and inspected regularly. The higher a cam’s lift, the more critical the valve springs are, and the greater the possibility of coil bind.

#11 - At first glance, this used valve spring may appear to be in perfect condition. But if you take a good hard look, you’ll notice that the top side of the upper two coils has a distinctive shiny band. This is evidence of coil bind. Two coils have come into contact with one another. While this wasn’t a severe case, because coils in the center of the spring don’t show any evidence of contact, coil bind severely stresses a spring and leads to failure.

#12 - When dual springs are installed on a set of heads, both inner and outer coils must be inspected for coil bind. This inner spring matches up with the outer spring in the previous photo. Even though inner springs are wound from thinner wire than outers are, they can still be subject to coil bind, especially if an improper retainer is installed. This spring failed because the retainer’s inner step was too tall. As a result, the inner spring was subjected to much more severe coil bind than the outer spring.

#13 - You’ve heard it a hundred times, "The first 20 minutes of a camshaft’s life are the most important." Here’s the proof. Excessive spring pressure during break-in, combined with insufficient lubrication, prevented the lifter on the right from rotating properly. As a result, the lifter bottoms and cam lobes wore excessively. Note how the surface of the lifter on the right is visibly cupped while the lifter on the left shows the correct circular wear pattern. All (non-roller) lifters should look like this. If they don’t, you can bet the matching lobes have had a bit of material removed from their surfaces. Flattened lobes not only leave cam grinders feeling unloved; they also mean a marked drop in horsepower.

#14 - Head gaskets can be an invaluable source of information about internal engine conditions. Note that the area between the cylinders on the right is darker and wider than the one on the left. That’s because it was positioned between two center cylinders of a small block Chevy where the exhaust valves are back-to-back. The localized heat generated by this valve placement leads to higher gasket temperatures and an accelerated relaxing of armor. This is the most likely place for leakage, leading to a blown head gasket, to begin.

# 15 - I heard it through the grapevine, this crank won’t last a long time. Even though this is a forged crankshaft, poor preparation and use of the wrong vibration damper led to a premature failure. Cast crankshafts are even more brittle and when one is used in a race engine, proper machining, precise balancing and a high performance vibration damper in good condition are absolutely essential to avoid failures.