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Bent Pushrod Symptoms and Causes – How to Diagnose and Replace

Pushrods can bend, though complete failure is uncommon.

A bent pushrod reduces the total lift provided at the valve. This could damage the camshaft lobe if it is resisting movement because it is making contact at some point where it ought not to. The bent pushrod could make contact with the lifter.

So, you see how important it is to know how to diagnose bent pushrod symptoms. This can help you manage the situation earlier enough to avoid catastrophic failures in the foreseeable future.

You can know when to stop driving with a bent pushrod and when to replace it with a new one.

Keep on reading to get to the details!

What Is a Pushrod?


car engine with valve and pushrod picture




It is a part of the internal combustion engine. This unique part is found in a pushrod or overhead valve engine.

The camshaft is found in the block near the crankshaft, but the valves are normally found in the cylinder head. A valve lifter rides on the cam. When the cam lobe comes in contact with the lifter, it rises and then transfers the motion to the pushrod. This action then moves a rocker, which in turn pushes the valve open.

The pushrod is also hollow. So, it helps channel oil from the lifter and through and out the rocker arm. The oil is necessary for lubricating the rocker arm and cooling the valve spring.

The pushrod is responsible for squarely centering the rocker arm over the valve tip. So, a bent pushrod could affect the performance of the rocker arm.

What Causes a Bent Pushrod?


pushrod and camshaft diagram




So, you pull the valve cover off and you find a bent pushrod. Some people may decide to buy a new pushrod and replace the bent one. What will you do if the new one bends right away? You first need to find the root cause of the problem and deal with it before replacing the pushrod.

Loose Valve Guide

Valve guides are the bushings that hold the exhaust and intake valves. Valve guide wear is very common and is certainly one of the principal causes of a bent pushrod.

What happens is that the valve guide lets loose from the casting and slides up. When the pushrod is pushing the rocker arm onto the valve tip, nothing moves. This is so because the valve guide is out of place, restricting movement. The weakest link (pushrod) is going to get damaged in the system. So, when the pushrod is trying to push up the rocker arm and the rocker arm doesn’t move, the pushrod is going to bend.

engine valve with guide



The valve guide may become loose because of the engine overheating. Some of the common causes of engine overheating include:

  • A malfunctioning thermostat
  • Running the AC on high for a long time
  • A bad fluid mix of water and antifreeze in the radiator
  • Running with a low level of fluid in the radiator
  • An engine in dire need of repair and servicing

Valvetrain Geometry

In some pushrod engines, the valvetrain geometry could be the culprit.

Non-direct injection motors have cylinders heads that were designed in a way that the lifter and the pushrod are perfectly lined up. The rocker is directly above the pushrod. So, bending was highly unlikely. But the oil pump in non-direct injection motors would lose oil pressure, causing the lifter to collapse and fail.

The new systems have a variable volume pump in them, which delivers as much oil as necessary to get the proper oil pressure needed. This has reduced lifter failures. But the problem comes with the new valvetrain geometry in some vehicles, where the pushrod sits in an offset position.

v8 pushrod engine image



When the system is running, the pushrod will not be moving in a vertical position in the up and down motion. Instead, it will be moving in an offset position. This type of movement of the pushrod causes it to rub against the lifter, creating a harmonic shock to the side of the pushrod. This can cause the pushrod to flex a little bit and end up bending in the long run. 

Bent Pushrod Symptoms

The bent pushrod symptoms you should be looking for include:

Engine misfire usually happens when the fuel charge in a cylinder fails to ignite. The issue generally occurs from a lack of spark, a fuel system problem, or internal engine damage like a bent pushrod. Misfiring wastes gas, causes a loss of power, and increases emissions. Your engine can misfire while running at a slow speed, on idle, or during hard acceleration.

The engine may produce a distinctive loud ticking sound. The ticking noise you hear normally comes from the lifter. A faulty or bad lifter is one of the most common causes of a lifter tick. The second cause of the ticking noise could be dirty oil deposits in the lifter. The third cause could be a bent pushrod, especially if you have a loose valve guide.

A rocker arm is one of the most important parts of the valvetrain. It is responsible for transferring the motion of a pushrod to the valve tip. A misaligned rocker will not be at the center of the valve tip because of the bent pushrod. 

A compression test is done to assess the mechanical condition of the engine. You might want to do a compression test if your vehicle has a misfire.

Inside an engine, you have cylinders, which are basically sealed chambers with controlled openings. The controlled openings are the intake and exhaust valves. The compression of the cylinder has to be normal for the engine to run optimally.

The first thing you want to do when conducting a compression test is to disable the flow of fuel to your engine. Next, disable the spark or the ignition. Then you need to pull your spark plugs one at a time with the help of a spark plug socket.

Attach your compression tester to where the spark plug was attached. Crank the engine a few times until the needle on the compression tester doesn’t move any further and record the reading. Repeat the same process for the remaining cylinders.

What you are looking for is for each cylinder to have a psi that ranges from 100 to 150. The readings for each cylinder should be fairly the same with no more than 10 percent variance across all the cylinders. If the compression test is low, then you probably have a bent pushrod, apart from other issues such as a leaking head gasket.

How to Diagnose a Bent Pushrod

If a valve for a specific cylinder doesn’t open or close, the cylinder in question will not run.

To diagnose valvetrain parts, you have to remove the valve cover on the side of the engine with the dead cylinder. Then visually inspect the two pushrods, valve guides, valve springs, and rocker arms for that cylinder.

Look for bent pushrods, misadjusted rockers, broken valve springs, broken rockers, and loose valve guides. Bent pushrods aren’t difficult to replace on most pushrod motors. If the pushrod is bent, carefully inspect the rocker arm for burrs. Then check the lifter to see if it is secure and hasn’t sprung out of its bore.

You also have to check the valve guide to make sure that it is intact and not loose. A loose valve guide may rise up, get stuck, and prevent the opening and closing of the valve.

How to Replace a Bent Pushrod

These steps should help you successfully replace a bent pushrod.

Step 1: Find the Bent Pushrod

Start by removing the valve cover on the affected part of the engine. Do a visual inspection of the rocker arms and check their alignment with the valve tip. If one of the rocker arms isn’t at the center, then the attached pushrod is probably bent. You can also wiggle each pushrod to single out the damaged ones.

Step 2: Remove the Rocker Arm

Remove the rocker arm attached to the bent pushrod for vehicles with individual rocker arms. If your engine, however, comes with a rocker shaft, then you will have to remove the entire assembly of the rocker shaft. This step will need a ratchet wrench and appropriate-size sockets.

Step 3: Pull Out the Bent Pushrod

Use your hand to pull out the bent pushrod. We also recommend you inspect the other parts of the valvetrain, including the retainers, valve spring, and valve guide.

Step 4: Install a New Pushrod

Install a new pushrod of the exact length as the old one by hand. The new pushrod needs to sit properly in the valve lifter. Then reinstall the rocker arm or rocker shaft assembly. While at it, make sure all the pushrods are properly seated in the valve lifters and the rocker arms are squarely centered.

Conclusion

A bent pushrod can do more than just affect the engine’s performance. It can cause damage to other parts of the valvetrain. So, it is extremely important to know the common bent pushrod symptoms. Also, replacing the damaged pushrod isn’t enough, you need to know what caused the pushrod to bend to avoid damaging the new one. 


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