Signs of a Bad Connecting Rod

Most of today’s car engines have a certain number of cylinders. While four-cylinder and six-cylinder engines are the most common, there are many eight-cylinder engines on the road as well. At the high end of the car market, there are exotic and luxury cars with ten-cylinder, twelve-cylinder, and even sixteen-cylinder engines.

For each cylinder that is part of a particular car’s engine, there is a connecting rod located within it. The connecting rod is a thick, flat piece of metal (usually steel) that connects at one end to the piston, and at the other end to the crankshaft. The connecting rod translates the up-and-down reciprocating motion of the piston into rotating motion at the crankshaft. The power that is produced by all of the engine’s cylinders, firing in a preset sequence, is transferred to the car’s transmission and then to the wheels, propelling the car down the road.

What are the signs of a bad connecting rod?

A bad connecting rod is usually the consequence of some other type of engine problem, and not the cause. Connecting rods do not generally fail on their own, but tend to malfunction as the result of a lack of proper maintenance, or the failure of another component. There are several symptoms of a bad connecting rod. Let’s check out what they are:

• Knocking sounds coming from the engine: The sound known as “rod knock” is usually caused by a lack of lubrication, which occurs at the bearings where the connecting rod’s vertical motion is used to rotate the crankshaft. Instead of having a normal film of oil that coats these moving parts and lets them move smoothly against each other, the unlubricated bearing material wears away, leaving you with metal-to-metal contact between the connecting rod and the crankshaft. Another possibility is that you have a “spun bearing,” where the connecting rod bearing spins out of position and blocks the oil passages. The end result, either way, is a knocking sound. Rod knock is most noticeable when your engine is running at a steady speed, and it will increase in speed as the engine speed increases.

• Low oil pressure/poor oil flow: This is another clue that your engine is getting insufficient lubrication. If dirty, sludgy oil is blocking your engine’s oil passages, the oil will have great difficulty in circulating through them. Low oil pressure may cause your dashboard oil warning light to illuminate, or it can produce a low reading on your oil pressure gauge, if your car has one. If you see the oil light or a low oil pressure reading, stop your car immediately, shut it off, and call your mechanic for guidance. Your engine may be in serious danger.

• Low oil level/excess oil consumption: This can be a result of the issues described above. Poor lubrication can lead directly to excess oil consumption, reducing the amount of oil in your engine. If you notice that this is a constant condition, and you have to add oil frequently, call your mechanic and have it checked out, before it gets any worse.

• Overheating engine: If your connecting rod lubrication problem is severe enough, the excessive amount of heat produced can overwhelm your car’s cooling system and cause overheating. If your temperature warning light comes on, or you see your temperature gauge hit “H” or go into the red zone, shut your car off immediately, and get in touch with your mechanic.

Should you drive a car with a bad connecting rod?

Definitely not. While a bad connecting rod can cause some serious damage in its early stages, the consequences of continuing to drive with a bad connecting rod can be truly catastrophic. If the bad connecting rod breaks while moving at high speed, its pieces can make a big hole, right through the side of your engine block. At the same time, the piston that the connecting rod was formerly attached to is free to do its own damage at the top of the cylinder, where it can smash into the intake and exhaust valves, bending or breaking them. This event is known as “throwing a rod.” Congratulations, you have just completely destroyed your engine.

How do you fix a bad connecting rod?

There’s no easy way to deliver the sad news. A bad connecting rod is a sign of serious engine damage. Even if you catch it before your engine throws a rod, there will be some major engine rebuilding in store for your car. The possible list of damaged items can include:

• The connecting rods themselves
• The connecting rod bearings
• The crankshaft
• The pistons
• The piston wrist pins The cylinder walls
• The valves
• Other related parts

Your mechanic will first need to disassemble your engine to the point where the extent of the damage can be assessed. The next step is to compile a list of items that need to be repaired or replaced, plus plenty of labor to go with it. This will be expensive.

If this happens to your car, you may have a difficult decision to make, depending on the news you receive from your mechanic. Based on the extent of the damage, and the state of the rest of your vehicle, your mechanic may offer you one or more of the following choices:

1. Repair your damaged engine and replace the parts that are no longer usable
2. Replace your entire engine with a remanufactured unit, which will come with a warranty
3. Get a used engine from an auto recycling yard – it will not have a warranty
4. Sell your damaged car to a scrap yard now, because the repair costs are much more than your car is worth.

The first option is for an engine with minimal damage. The second option is worth doing if your car is fairly young and has plenty of life left in it. The third option is an inexpensive way to keep an older car running a little longer, and it will also allow you to sell your car in running condition, which will bring you a higher price. The final option makes sense if your car is old and worn, and will not be generally reliable just because you replaced the engine. If the last one sounds like your car, it may be time to say goodbye.

Can you replace a bad connecting rod by yourself?

Unless you have extensive experience in rebuilding engines, the answer is NO! A bad connecting rod can mean that there is extensive engine damage that will require sophisticated skills and specialized tools to repair. It’s definitely not your typical DIY job!

You can prevent a bad connecting rod

If you have been reading this because you already have a bad connecting rod, we sympathize. But if you are reading for purely educational purposes, here’s a very important takeaway: Preventing connecting rod problems is a much easier and less expensive course of action than having to pay for an expensive repair (or scrapping your car) after it happens!

Are you one of those drivers who tries to save a few dollars by not having your car serviced? If so, you could come to regret that bad decision. Not changing your oil will put you in the penalty box when your engine destroys its connecting rods and crankshaft, along with other moving parts. Changing your oil at the recommended intervals (check your owner’s manual) is cheap insurance against a bad connecting rod, as well as many other car problems.