A two-cent washer becomes the unlikely starting point for an expensive AMG engine failure, but the mechanical explanation quickly grows more complicated than that headline suggests. The damaged E63’s previous owner had doubled up spark plug washers while attempting to orient the plugs correctly, and the resulting engine suffered a broken piston ring land and damaged cylinder. Mercedes documentation is presented as warning that incorrect spark plug orientation can contribute to this type of failure, yet the host sensibly ends up attributing the destruction to a likely combination of the extra washer, improper orientation and an aggressive tune rather than pretending that one variable has been conclusively proven responsible.
Replacing the destroyed M157 with an $11,500 used engine provides a substantial repair project in its own right. Unfortunately, the 48,000-mile replacement came from a badly fire-damaged vehicle and had apparently been sitting for roughly six years, creating plenty of uncertainty. Walnut blasting the carbon-covered intake valves, cleaning the engine, replacing numerous difficult-to-access seals, a vacuum pump, coolant components, engine mounts and the rear main seal demonstrates the practical advantage of preventive maintenance while the powertrain is already removed. The explanations are generally accessible enough to make an extremely involved AMG repair understandable without pretending it is simple.
That replacement engine produces its own worrying discoveries. Old fuel, rust, coolant around injector areas and incorrectly installed seals eventually force removal of the cylinder head covers, while the injectors are cleaned and subjected to basic testing. Importantly, the host acknowledges the limitations of his roughly 122-psi injector machine compared with the thousands of psi encountered in the actual direct-injection system, describing it as useful for finding gross problems rather than claiming it provides a definitive flow test. Reusing the recently operating injectors from the failed engine after cleaning and resealing them is explained as a judgment call rather than presented as unquestionably correct.
The most interesting development comes when the spark plugs refuse to index according to the Mercedes guidance. Bosch plugs that had aligned well in one cylinder head consistently point roughly 90 degrees away from the desired direction in the replacement engine, while Mercedes-branded plugs produce similarly troublesome results. NGK plugs unexpectedly align better in the replacement engine despite the host saying Mercedes documentation advises against them. Repeating the experiment across several cylinder heads and plugs makes the investigation considerably more persuasive than a single observation, even though it still cannot establish why the differences exist.
Changing the thickness of the spark plug's existing crush washer eventually provides a practical solution. A thinner replacement washer demonstrates the principle, after which the original Bosch washers are carefully reduced to approximately 1.30–1.35 mm until the plugs fall within the desired orientation range at the specified 23 Nm torque. Crucially, the host repeatedly warns against adding a second washer and recommends checking each individual installation rather than assuming one measurement applies universally. That distinction is important because modifying spark plug sealing washers is unconventional work with potentially serious consequences if performed incorrectly.
The weakness comes when an intriguing mechanical finding develops into allegations that are not actually demonstrated. The host speculates that inconsistent cylinder-head threading could represent a Mercedes manufacturing problem and goes further by suggesting the company's technical document may provide “plausible deniability” for rejecting engine warranty claims. He explicitly admits having no proof, and nothing shown establishes Mercedes' motives, warranty practices or whether the observed indexing differences constitute a manufacturing defect. Testing four cylinder heads and several plugs raises a legitimate technical question worth investigating, but it cannot support the broader accusation without substantially more evidence.
Presentation is energetic and unusually transparent about mistakes, uncertainty and changing plans. The failed four-hour deadline becomes part of the story rather than something edited away, and discoveries such as the coolant contamination genuinely alter the repair as it progresses. There is nevertheless considerable excess around an already lengthy job: repeated jokes, cleaning sequences, sponsor material, giveaway promotion, turbo painting and numerous “while you're in there” repairs push the central spark-plug investigation deep into the runtime. The upgraded VRP turbos and downpipes also broaden the project beyond merely repairing the original failure, and the episode ends before the replacement engine actually runs, leaving the ultimate success of the repair unresolved.
Pros
- Repeated spark plug tests across multiple plugs and cylinder heads reveal a genuinely interesting indexing inconsistency rather than relying on a single observation.
- The host clearly distinguishes the dangerous double-washer approach from his eventual method of modifying the thickness of a single existing washer.
- Extensive preventive maintenance and inspection provide substantial practical detail about servicing an M157 while the engine is removed.
- Limitations of the injector test equipment and uncertainty surrounding the fire-damaged replacement engine are openly acknowledged.
- Mistakes, unexpected contamination and the failed four-hour deadline give the mechanical work an unusually transparent trial-and-error quality.
Cons
- Claims that Mercedes may have a cylinder-head manufacturing defect or use its documentation to create “plausible deniability” for warranty denials remain speculative and unsupported by evidence of corporate intent.
- The washer modification is consequential mechanical advice, yet the testing shown cannot establish that it is necessary or appropriate across M157 engines generally.
- Sponsorship, giveaway promotion, turbo upgrades, extended cleaning and numerous side repairs make an already complex investigation considerably longer and less focused.
- The replacement engine never runs during the episode, so neither the engine swap nor the modified spark plug setup receives an operational test.
What begins as an AMG engine replacement develops into a surprisingly absorbing investigation when supposedly correct spark plugs refuse to align consistently across different cylinder heads. The repeated testing makes the mechanical puzzle worth taking seriously, but the leap from that puzzle to suspected Mercedes manufacturing and warranty strategy goes beyond what the evidence establishes. Despite its sprawling runtime and unresolved ending, the combination of detailed wrenching, transparent troubleshooting and a practical indexing experiment makes this a compelling project installment.
