Anti-Polish Rings: Do I Need Them For My Diesel Engine?

Like most engine design changes, anti-polish rings (APRs) were created with a particular purpose in mindto remove carbon buildup from the piston.

APRs are a solution, rather than a problem that will harm your VGT. Today, we'll take you through how APRs work, why they were developed, and what can happen if you end  up with carbon buildup in your pistons. 

We also have a video on the topic, if you want more information:



Do you need new pistons and liners for your diesel engine? Our ASE Certified Technicians can help you get exactly what you need for your repair!

Give Us A Call!


What is the Purpose of APRs in my Diesel Engine? 


diesel engine piston ring | Highway & Heavy Parts


Wondering why anti-polish rings might be beneficial to your engine? 

Well, the APR liner is designed to knock the carbon off of the piston. EGR engines put exhaust gas back into the intake side of the engine. So, because we're introducing this exhaust gas back into the engine, a larger amount of carbon buildup began to occur on the pistons. That, in turn, has increased the amount of carbon that builds up on top of the piston. It would actually go down the side of the piston and then the top piston ring would stop floating.

Why is this a problem? Well, the job of the top piston ring is actually to move back and forth as the piston goes up and down. It doesn't actually travel in a straight line. There's a bit of an arc to it as the throw of the crankshaft comes up and down. This causes two sides of the cylinder bore to wear more. If that piston ring seizes and doesn't float, you get bore polish. 

So, as the carbon would creep down on the piston, the top ring would seize up, causing that bore polish, blowby, and oil consumption. APRs were designed to prevent this from happening. 

Are APRs compatible with your engine? Read our earlier post on anti-polish rings to find out. 


How Diesel Engine Manufacturers Designed APRs

 The whole reason the APR was designed was to make emissions cleaner. When manufacturers made the EGR engine, they didn't forecast that there was going to be a problem with carbon buildup.  So, they had to develop something to fix the problem.

Thus, the anti-polish ring was born. They developed APR liners and pistons. Yes, the piston had to change too. What that means is they've taken the liner and machined out the top and put in an insert. This insert is a reduced diameter, and covers just the very top travel of the piston. So, as the piston comes up through the APR, it is designed to knock the carbon off. 

What the manufacturer had to do with the piston was reduce its diameter and the diameter of the lower top ring. So, the top ring has actually moved down on the piston. 

The name "anti-polish ring" is actually a bit misleading. The ring isn't actually polishing anything, but it's knocking chunks of carbon off. Before that carbon starts to collect in large amounts, the ring knocks it off as the piston comes up. 

In a perfect world, the carbon would go straight out the exhaust. But, it has to travel through exhaust valves, the turbo, the DPF, and the after treatment. Basically, it's important to keep the particles as small as possible to get them out of the engine without damaging the after treatment.

Read our blog on diesel engine emissions to learn more about requirements that might affect your diesel engine!


What is Blowby?

As we mentioned earlier, blowby is one of the symptoms of bore polish. Blowby is measured by how much compression, or how much gas is coming out of the crankcase.

So, in gasoline cars, a lot of engines have now gone to a closed crankcase where all the gasses stay inside the engineit's not vented externally. On the diesel engine, we have what some people refer to as the blowby tube, which is really a crankcase vent.

The amount of pressure that builds inside the engine, if it's too great, will actually blow out seals. You may have heard drivers complain that their dipsticks are blown out. That's because the pressure inside the crankcase of the engine has exceeded its ability to vent it.


What Causes Crankcase Pressure?


diesel apr ring crosshatch | Highway & Heavy Parts


There are multiple causes of crankcase pressure. The largest in this case is when the piston rings can no longer seal to the cylinder walls. Cylinder walls have crosshatch, which is a manufacturing machining process that puts the right friction on the side of the liner, matching with the piston ring. That's what you're actually doing when you break in your engineyou're seating the rings into the liner, so as the piston goes up you're compressing air on top of the piston.

The pistons aren't really sealing or doing anything. The piston provides the ride for the rings, which are sealing the air to the cylinder wall. So, if the liner has bore polish, it means that crosshatch has worn away. This results in the cylinder being polished like a mirror, and the ring can no longer seal against the cylinder wall. Now, some of the air can go down past the piston rings.


diesel apr failing egr systems | Highway & Heavy Parts


Failing liners can harm EGR System components downstream such as plugging your DPF filter, damaging the nozzle ring of your VGT from carbon striking it upon exit, or high levels of soot build-up can seize the vanes of the VGT.  APR Liners are a durable solution versus standard pistons and liners.  While it cannot eliminate carbon from your diesel engine, itll make the carbon into little particles thatll help your EGR System manage the pollutants better than large, damaging pieces.


Want to know more about anti-polish rings for your diesel engine? Call us at 844-304-7688 to talk to one of our ASE Certified Technicians. Or, you can always request a quote online!