Piston repair, although not recommended by automotive experts, is often an option when. rebuilding a car engine. The information in this chapter aims to provide you with information about how to fix pistons by changing the replaceable piston parts. I will also be exploring the costs to do so, both as DIY projects and by a professional engine rebuilder.
Can you Fix Car Engine Pistons?
Engine pistons at made of wear components such as rings, bearings, and bolts. These tend to wear down over time, leaving the other parts in good condition. When that is the case, you may want to change the bad parts and not the entire piston assembly.
The answer, therefore, to the question is that yes, you can repair pistons. It’s also important to note that piston repair only works in the short term. By the time you have worn piston rings or piston bearings and bolts, the rest of the piston has already suffered the beating.
Nevertheless, fixing a piston whose wear parts are damaged offers the advantage of cost savings. Pistons are pricey car parts and an effort to salvage them can see you save a few hundred dollars. Let’s see how to go about repairing your car engine pistons, but first, how to do a piston diagnosis.
How to Check Piston Damage
Piston diagnosis can be done in a variety of ways. In situations where the piston is damaged, symptoms such as loss of power or smoke and engine noise will appear. These are the first signs of piston problems. To confirm damage, though, it’s usually necessary to go further and carry out tests. You may also want to remove the pistons and inspect then manually. The ways to diagnose engine pistons include:
- Compression test
- Leak-down test
- Physical Inspection
Piston Compression Test
A compression test reveals the condition of the piston rings, if they are worn and allowing combustion gases to leak. Have with you the following: compression gauge, spark plug socket, ratchet set, and extension.
- Ensure the engine is warm but not too hot. You can start and let it run for 5-10 minutes.
- Switch off the engine
- Locate the fuel pump or injection fuse using your manual and remove it. Remove the ignition coil fuse as well.
- Remove the spark plug wires and ignition coils. Mark them to make refitting easy.
- Using the spark plug socket, ratchet and extension, remove the spark plugs.
- Insert the compression hose or adapter into the spark plug hole of the first
- Connect the compression gauge.
- Crank up the engine for about 10 seconds or up to 4 times. This is enough for enough cylinder pressure to build up.
- Read and record the reading on the gauge.
- Connect the gauge to the next cylinder until you have tested them all.
Typically, compression pressure should range from 125 psi-160 psi. If too low, the piston rings could be too worn or damaged and leaking. If testing a diesel engine, peak psi readings should be slightly higher and range between 275 and 400 psi.
You may also perform the wet compression test for cylinders that show less than 100 psi. This test involves pouring a tablespoon of oil into the cylinder and repeating the test. The readings should rise to indicate worn piston rings.
Piston Leak-down Test
This is the opposite of the compression test. Instead of measuring the ability to accumulate pressure, you introduce it into the cylinders. The things you will need are: compressed air source, leak-down tester, spark plug socket, ratchet set, and extension.
- Remove the spark plugs.
- Rotate the engine so the piston is at TDC (top dead center). A simple way to do so is by using a long screw driver. Insert it into the spark plug hole and slowly rotate the engine. The TDC is reached when the screwdriver just starts to go down after rising.
- Connect the threaded adapter hose into the spark plug hole.
- Connect the source of compressed air
- Turn the regulator and set the air pressure to between 80 and 90 psi or no higher than 100 psi. This will pressurize the cylinder.
- Turn the regulator to zero then connect the leak down tester to the cylinder.
- Read the gauge that indicates leakage in percentage.
If the reading is more than 20%, there’s a leaking problem. Listen in to detect the source of leak. If in the dipstick hole or crankcase vent hose, the piston rings are probably worn and damaged. Repeat the test on all cylinders.
Physical Piston Inspection
A visual examination aims to confirm the piston damage. You can do so with the piston inside the cylinder. However, you would need a special tool which may not be available. A different way is to remove the piston from the engine.
A bad piston will have eroded or burned parts, especially at the top part. Piston ring damage includes breakage, scoring, or expansion. In severe situations, a piston head may have shattered from heating the valves or the connecting rod broken. Piston bearings will also wear down.
You can also carry out piston measurements to measure clearance using a feeler gauge. Excessive clearance indicates piston ring wear. Combined with the other methods for piston diagnosis, you can then opt to change individual components or entire assembly.
Piston Repair Options
As we have seen, you can only repair an engine piston by changing bad rings, worn bearings, and damaged piston bolts. These parts are also sold in the auto parts market, either as separate parts or in a kit. Below is a description of what entails the different ways to fix engine pistons.
Piston Repair by Replacing Rings
Piston rings usually wear down over time, or they can deform under the harsh conditions inside the cylinder bore. In order to replace them, the piston must come out of the engine. Different types of piston rings also go into different grooves.
Damaged rings cause blow by, over consumption of oil, and other symptoms of bad piston such as piston slap. Before changing them, it’s crucial to perform tests such as the compression and leak down test. A physical examination is also required.
Installing piston rings requires one to follow the replacement instructions. That’s because incorrect installation can result in engine problems of even piston damage. You also need various tools such as the piston ring expander.
Most of the time, the cylinder bore requires machining in order to accommodate the new rings. This is usually better done at a repair shop, or by an engine rebuilder.
Piston Repair by Replacing Rod
The connecting rod joints the piston assembly to the crankshaft. It rarely gets damaged, unless when an incorrect piston is used in an engine. The rod may also break if the timing goes wrong and the piston hits the valves, or if the bearing is starved of oil and seizes.
In order to replace piston rods, the piston assembly itself must be removed. Rod installation is a labor-intensive job that many people might not want to undertake. Selecting the correct rod for your engine might also be cumbersome, given the many different materials use to make them.
Aluminum alloy piston rods are best used on mild engines since they offer little in terms of strength. That’s unless it’s a high quality alloy. For robust rods, steel is more preferred. Titanium is another excellent material but too costly.
Piston Repair by Replacing Bearings
Piston rod bearings are positioned at the big end and small end of the connecting rod. The piston needs these crucial parts to operate smoothly. To replace them, you only need a few tools and materials.
Piston bearings get damaged in many ways such as oil starvation that causes excessive friction and wear. Particles in the oil or from other sources can also cause abrasion and wear down the bearings.
You can easily replace bearing without removing the engine or pistons. However, you would need to raise the car and access them from underneath. There are also the undercarriage parts and the oil pan to remove.
Piston Repair by Replacing Bolts
These are also known as the connecting rod bolts and located at the point when the piston and crankshaft meet. The process to replace bolts requires regular tools such as torque wrench, ratchet and socket set, and some lubricating oil. You also need the manual with you.
Conrod bolts can get damaged in many ways. Most of the time, it’s the violent piston movement that take a toll on them. Corrosion also causes damage or the wear that happens over time and loosens the bolts.
The bolts are made from a wide range of materials such as steel, aluminum, and nickel alloys. They also come in different designs. It’s crucial to match the bolt specifications with those installed on your engine. Most importantly, ensure the correct torque during their installation.
Piston Repair Cost
The cost to repair pistons depends on the type of damage. It also depends on the damaged piston parts. As already indicated, most repair options require the removal and replacement of these major components: rings, rod, bolts, and bearings.
Most of the parts when fixing an engine piston cost between $30 and $150. Labor charges, on the other hand, range from about $100 up. Generally, the amount depends on the type of component being changed.
The piston ring installation cost, for example can be between $100 and $200 or more depending on the type of engine or car. New bolts and bearings cost around the same amount. Adding the total costs, the amount to repair engine pistons can up to $500 and higher.
It’s advisable to ensure the piston repair cost is not too high, though, especially if having it done by an engine rebuilder. If too high, consider installing new pistons instead. That way, you will get many more miles and save money in the long run.
Piston repair is a time-consuming process. You need to disassemble engine parts, some of which take slot of time to remove or out back. Most of the time, though, engine pistons require replacing. That’s because most parts will already be in a bad state. The steps to do so are explained in detail in the next part of the guide, including the cost.