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If you’ve ever heard a strange knocking sound coming from your engine — as if someone were gently rapping against it with a small hammer — it could be coming from a condition known as rod knock.
What is Rod Knock?
As your car gets older, the bearings that hold its engine’s connecting rods to the car’s crankshaft wear down, causing a gap to form. As you can imagine, given that your engine spins at thousands of RPM, the result is the parts slapping against each other. Rod knock is the phenomenon that occurs when your engine’s connecting rods strike the crankshaft as it spins.
What Kind of Problems Does This Cause?
At first, rod knock just produces a mildly irritating sound, but as you can imagine, bigger problems arise when it’s left unchecked. The more the connecting rods and bearings knock against the crankshaft, the more the surfaces of each will wear away, and heat will build up as lubricating oil won’t provide the safety cushion it once did.
Let these problems exacerbate, and the result is a broken engine, which can manifest in some spectacular ways, up to and including throwing a rod right through your engine block. As such, though fixing rod knock is expensive, it’s not as costly as total engine failure.
What if the Sound Isn’t Rod Knock?
If you determine that the noise isn’t a result of rod knock, your timing belt tensioner may be loose or broken, your air conditioning compressor may be going bad, the flywheel could be cracked, the valves may be sticking, or you could have an exhaust leak. Take your car to a mechanic to have each of these other possible sources eliminated.
How to Fix Rod Knock
Unfortunately, the only way to fix rod knock is by rebuilding the engine. The good news is that not all engines are created equal, meaning the job is easier for some than others, but the bad news is that it’s never really “easy.” The engine will most likely have to come out of the car, followed by the oil pan and crankcase.
If you’re lucky, the head(s) can stay on the engine, and if you’re really lucky, the crankshaft will have only suffered minimal damage, if not none at all. The crank journal, which is where the rod bearing holds on, will probably have to be resurfaced, which will remove some of the material, but that’s okay, given that the replacement rod bearing will be thicker to compensate.
Keep in mind that the entire procedure isn’t one that you can perform indefinitely. There’s a limit before the crank gets shaved down too much to remain useful.
Preventing Rod Knock
Rod knock is a problem no one wants, so here’s how you can prevent it:
Use High-Quality Oil
Use the right viscosity and buy the good stuff, and always make sure there’s enough in your engine!
Don’t Go Past Redline
Excessive engine speeds put huge amounts of pressure on rotating parts. Your engine wasn’t designed to exceed a certain RPM, so stay in the safe range.
Summary: If you hear a slight “knocking” sound coming from your car’s engine, it could be a sign of rod knock. Since rod knock can lead to catastrophic engine failure, it’s essential that you get it diagnosed and fixed as soon as possible.