Destroying A Ford 302 - Kablooie!

It's junk! The call went out just moments after smoke filled the dyno room and while a hunk of the engine block was still spinning on the floor. It was the first engine we'd seriously hurt without meaning to, and just the fifth rods-outta-the-block explosion in Westech Performance Group's 10 years of testing. And we're talking wrecked. With holes in both sides of the block and several in the oil pan and major damage to both heads and the cam, about all we walked away with was the carb, intake, valve covers, and 15 rocker arms and springs. The rest is in the dumpster.

But why? With hundreds of dyno pulls per year, we knew we'd eventually send an engine to the graveyard, but we hoped we could do it in glorious fashion on a serious nitrous pull, or at least under boost. Then there'd be some pluck to it. This one was a mild 302 Ford with maybe 50 dyno pulls on it. It had been used for the "Cam & Intake" story in our November '01 issue and then stuffed under the bench for a few years. We'd planned to use it this month to compare nitrous and blower cams, but it fragged before it even sniffed a power adder. The engine had just 9.1:1 compression, and we were running it on 100-octane Rockett Brand fuel with 30 degrees of total timing. There was no chance of detonation, and we had a mile of piston-to-valve clearance. It just didn't make sense that it would come apart, but it did-and at only 5,800 rpm. We had to know why.

In fact, when parts fall out, it's always important to find the cause so you can learn from the experience and prevent it from happening again. In this story we'll walk you through the teardown of our toasted 302 and share our observations and powers of deduction that lead us to the ultimate cause of the engine's demise. It's gearhead forensics, or CSI Westech. The investigation starts now.

There was no huge noise when it let go, just a huge cloud of oil smoke in the dyno cell. The assessment of the engine's demise was immediate, and it took freelancer Steve Dulcich 15 seconds to pen the ritual "I'm Juuuunk" on the front of the engine. If you find yourself in a similar circumstance, avoid the temptation to start ripping junk apart. Using a methodical teardown is the best way to inspect each part and find out what went wrong.	This was our first clue: Windows in both sides of the block and an inch of oil-ring shrapnel hanging out of a fresh gash in the underside of the pan. Clearly a connecting rod had let go, but was it the first failure, or symptomatic of another problem?	With lesser engine failures such as bad injectors, leaky valve guides, or blown head gaskets, the spark plugs are often the first clue as to which cylinder sucked up the damage. Pull them out and inspect for wetness from fuel, oil, or water, or for little specks of aluminum that indicate aluminum spatter from a piston that's been abused with detonation or lean burn. In our case, the physical damage to the end of the plug said we were way beyond a tune-up. Seeing light through the plug hole and out the other side of the engine was also not good.
Careful inspection and disassembly of the valvetrain can teach you a lot. You want to look for misalignment and broken parts not only to find the problem, but to take a careful look at the non-broken cylinders to discover if damage could have been caused by problems such as bad valve adjustment, rockers slipping off the valve tips, or pushrod interference with guideplates or cylinder heads. A bent pushrod can also be telling. All we found was one bound-up exhaust spring and rocker.	Two cam lobes had physical damage from contact with a broken connecting rod, and the lifters from those lobes had wiped out the roller axles even though the lifters themselves looked OK and even spun freely if you didn't put a little load on them. Had we not been paying attention during disassembly, we may have reused them and had another engine failure.	Upon removing the carburetor, we spotted fragments of aluminum in the intake manifold, which could be nothing but dead piston material. This is important to note, as junk that gets barfed into the intake can often find its way to another cylinder. Knowing the possibility can help you diagnose primary and secondary damage. Sure enough, a big hunk of piston swapped cylinders and killed a cylinder head on our 302.
And now a moment of comic relief: When we removed the right header, we heard something rattling inside and poured out this handful of piston debris. Even more had been blown into the wall at the back of the dyno cell.	Forged pistons are ductile enough that something like a valve head or a loose bolt in the cylinder will embed in the piston, or at least make a witness mark before it stabs a hole in the piston. That's not the case with hypereutectic pistons, which shatter like glass. We inspected the bigger hunks in the bottom of the oil pan for any evidence of a foreign object in the cylinder, such as an air-cleaner nut or anything that could have been wedged between the valve and its seat, but found nothing.	The witness marks in the combustion chamber made it very unlikely that the connecting rods let go first, because if that were the case, the piston wouldn't have kept smashing the broken valve into the head. We found five pieces of this broken rod, the biggest of which was still spinning freely on the crank. Inspection of the bearings showed no damage from debris in the oil, and no bearing pounding or loss of bearing crush that would be indicative of detonation.