Engine Forensics: Assessing Piston Failure With MAHLE Motorsport

Regardless of whether it runs on diesel, is a high-compression, high-winding N/A build, or is just a pump fuel-powered project car, every time an engine explodes, a thorough investigation is sure to follow. Head gaskets, fuel injectors, turbos, exhaust manifolds, valves, piston rings, oil pumps… every component in the motor is presumed guilty until proven innocent.

It doesn’t matter which portion of the engine took a dirt nap. What matters is why it happened in the first place. That, and how much damage did said component’s failure cause in other areas of the engine?

This is why MAHLE Motorsport has, and continues to stand by its promise to investigate the root causes of piston failure. Not just from a product testing angle, but from a quality control and customer support standpoint as well.

All too often people see a destroyed piston, and they immediately presume that the piston was at fault. When in actuality it could be any number of culprits, with human error being prime suspect number one. MAHLE’s Joe Maylish recently dove into the topic during one of EPARTRADE‘s weekly webinars and shed some light on the process. 

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Photo Credit: EPARTRADE/YouTube

Internal Combustion Deconstruction

MAHLE’s dedication to determining precisely what went wrong when one of its pistons “grenades” has just as much to do with reconstructing the incident, as it does with determining the guilty party.

Being that MAHLE is world renowned for using top-tier materials and forging processes, as well as its acute attention to detail, the issue typically stems from one of the following, and not the product itself.

  • Improper Installation
  • Tuning Technicalities
  • Fueling Flaws & Spark Concerns
  • Picking the Wrong Piston
  • Detonation Disasters
  • Cylinder Wall Scuffing
  • Unforeseen Overheating Issues
  • Running Too Much Boost
  • Laughing Gas Overload
  • And More…
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Photo Credit: EPARTRADE/YouTube

Piston Forensics 101

There are a ton of other things that could potentially go wrong in an engine block outside of the abbreviated list above.

If a wrist pin clip isn’t inserted correctly, boom. Got a hairline pressure crack forming within a connecting rod bolt, or a bolt that wasn’t installed properly? Kerflooey. Time for a fresh engine build.

However, it’s not always a big-ass explosion that causes a piston to fail. Oftentimes it’s a continuous, gradual grinding scenario that is the harbinger of doom. For instance, MAHLE mentions that contamination or combustion buildup can cause the skirt to start scuffing the side of the piston bore wall, thus leading to overheating over time. This typically results in the formation of an uneven ring groove, and a pinched ring that is stuck in a set position will never rotate like it should.

Insufficient clearance is another consideration, where piston-to-wall miscalculations screw the proverbial pooch. Granted, this is something that a quick dyno pull often exposes, but even then you’re still going to have to do a full teardown to ascertain what the issue is and make a fix.

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Photo Credit: EPARTRADE/YouTube

Your piston is the boxing mitt. It’s the one taking all of the contact… [and] it’s not plug-and-play. It is application specific. — Joe Maylish, Sales and Program Manager for MAHLE Motorsport

Now as for crappy combustion and detonation issues, these concerns are equally well-founded. Either one can cause pistons to prematurely fail with the fury of a thousand smoldering Subaru head gaskets. This is especially true when too much fuel, the wrong kind of fuel, incompatible spark plugs, or an improperly calibrated tune come into play.

Broken ring lands, or having a ring gap that is off by a fuzz can also cause all kinds of mishaps to occur. All of that excessive energy has to escape somewhere, and when it does, that additional pressure can cause the rings on a piston to fail or even compromise the structure of the piston itself. 

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4032 forged alloy pistons don’t expand nearly as much when placed under intense heat for extended periods of time. However, a MAHLE piston rocking a 2618 alloy does expand when exposed to higher temps and pressure. Photo Credit: EPARTRADE/YouTube

A Never-ending Dedication to Detective Work

So what do you do if your  MAHLE piston-equipped engine decides to suddenly take a dirt nap, and you discover kaput pistons inside? You contact MAHLE Motorsport and explain the situation, providing any imagery they request to ascertain the cause of the failure. From there, the MAHLE team will let you know if it is best to send the compromised component(s) in for evaluation.

The more materials that MAHLE’s “forensics unit” has to assess the better too. So be sure to include any accompanying components like connecting rods, piston rings, and bolts along with the piston itself if possible.

Being that the cause of a demolished piston can be multifaceted, the task of recreating what transpired can be both convoluted and time-consuming, so it’ll likely be a hot minute before the motive is established. That said, MAHLE Motorsport stands by its commitment to helping its customers and race partners understand what went awry and why, and then suggest what to watch out for on the next engine build.

And yes, MAHLE Motorsport still logs every customer issue encountered with one of its pistons, and is forever updating its database. For it is painstakingly tedious steps such as these that prevent the same failures from occurring in the future. Make sure to watch the full EPARTRADE webinar linked above and stay up to date with all of EPARTRADE’s weekly industry webinars.  

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Photo Credit: EPARTRADE/YouTube

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Micah Wright

Raised on LEGOs by grandfathers who insisted on fixing everything themselves, Micah has been a petrolhead in training since age four. His favorite past times include craft beer, strong cigars, fast cars, and culinary creativity in all of its forms.
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