Your car is idling and you’re impatiently waiting, listening to engine noise. You have places to be and time is running out. It sounds like someone keeps banging on your oil pan with a hammer, rhythmically rap-rap-rapping. If your car's has a broken engine you can consider selling your car online or read on about engine rod knock.
But there’s no one under your car and no one is knocking on your engine. The noise comes from deep in the bowels of your motor. When you rev up the engine, the pitch and frequency changes. At one point, it sounds like the knocking noise nearly disappears. When you let off the gas, it continues and maybe even gets louder.
This is what rod knock sounds like. It doesn’t ever get better on its own, although when your engine is cold, the noise might be lesser. These car engine sounds are also commonly known as engine knock, spark knock, and engine pinging.
Technically, it’s a condition that occurs from excess play. Your engine’s pistons move up and down from ignition by the spark plug, with force enough to rotate your crankshaft. Connecting the piston and crankshaft is a connecting rod. And your connecting rods is bolted on the bottom side around the crankshaft with smooth, thin metal bearings between the surfaces.
During engine rotation, these metal components would all overheat and seize together if it weren’t for engine oil. It lubricates the moving parts, allowing them to slide over each other frictionless. It also fills in the minute gap between the bearings and the crankshaft.
Rod knock occurs when the bearing has been partially or completely destroyed. It’s usually due to oil starvation although bearing wear can happen naturally over hundreds of thousands of miles.
On the flip side (literally) is the wrist pin. It’s a hollow pin that holds the piston to the top of the connecting rod. When there’s wear on the wrist pin, a condition known as piston slap occurs. The piston is slightly loose and wobbles in the cylinder, making extra noise.
Keep in mind that rod knock and piston slap are both caused by incredibly small changes in tolerances. We’re not talking about a quarter of an inch – we’re talking in terms of thousandths of an inch! That seemingly minor gap allows for enough movement to cause rod bearing noise because metal parts can now bang against each other.
Your engine will never be the same, rod knock will eventually turn into a much, much larger problem. That annoying engine knocking sound evolves into a clatter as the bearing surface erodes more and more. When the bearing has been annihilated – which doesn’t take very long – the bearing welds itself to the crankshaft and the connecting rod flops around the crankshaft. If the connecting rod binds or jams, it can break away from the crankshaft, known as a thrown rod. It’s going to really grind things up in your engine’s bottom end, possibly even blowing a hole right through your engine block.
A rod knock repair cost has a number of variables:
How long has the noise been occurring?
How much damage has the engine suffered?
Have metal shavings circulated throughout the engine?
Is the engine high-performance or specialized?
Is the engine salvageable?
If you catch the problem early enough, an engine overhaul may get you all fixed up. The engine must be completely stripped down to a bare engine block for inspection. If the cylinder walls are scored badly, you may need to replace the engine altogether. Minimal scoring can sometimes be honed out and oversized piston rings used. So, you could be facing the decision of whether to fix your car or sell it as-is.
Connecting rod bearing replacement costs have to factor in all the additional parts as well. You’ll need new engine seals and gaskets, cylinder head bolts, connecting rod bearings, and a bunch of money to flush the engine and cooler lines. Depending on the extent of the repair, you may need new pistons and connecting rods, camshaft bearings, timing chains, and potentially a new crankshaft. If you need all the extra parts, you’re better off replacing the complete engine assembly.
An average connecting rod repair will cost anywhere from $2,500 and up. On some vehicles like a Subaru Forester, that can run $5,000 between parts and labor for an engine rebuild or beyond $6,000 for a whole new engine replacement.
A better option avoids downtime and out-of-pocket repair expenses. You can sell your car to CarBrain for a fair price, just as it is. You don’t have to worry about your car’s current state – we’ll give you a guaranteed offer based on its current condition. Once you accept our quote, we’ll send someone to pick up your car and you’ll be paid on the spot. It’s a rapid solution for an expensive, drawn-out problem.
Yes, rod knock is a serious issue. If you cannot identify what is wrong quickly and continue to drive the car, the damage caused by whatever is creating the rod knock sound can eventually lead to a completely failing engine.