MOTOR Magazine

A MOTOR Magazine Newsletter
November 22, 2016

Contributed by Bob Chabot
Minimizing Timing Chain Wear

R&D and lubricant formulation improve timing belt wear on GTDI engines

Timing chain wear is becoming an area of increasing concern for OEMs, particularly with gasoline turbocharged direct injection (GTDI) engines, according to Ryan Rieth, lubricant development technologist for Infineum International Ltd. He and the company recently shared with MOTOR several insights about timing chain wear and how proper analysis and quality lubricant formulations can improve durability.

Besides improving timing chain wear, Infineum shared other lubrication trends that are part of its R&D program. (All images — Infineum International Ltd.)

MOTOR: What is behind interest in improving timing chain wear?

Reith: Tightening emissions legislation is the primary driver, since automakers have found minimizing timing chain wear helps avoid noncompliance. The engine oil lubricates metal timing chains in passenger car engines. They connect the crankshaft to the camshaft, which in turn controls the opening and closing of the intake and exhaust valves. Over extended periods of routine use the timing chain gradually elongates, which can eventually disrupt intake and/or exhaust valve timing. This in turn leads to engine inefficiency and increased emissions. That's a problem that quality lubricants can help.

MOTOR: How are OEMs and lubricant manufacturers cooperating to address wear?

Reith: Gasoline turbocharged direct injection (GTDI) engines, designed to boost fuel efficiency, are featured in many new vehicles today. But early timing chain wear in those engines has become a concern for OEMs. To address this concern, the International Lubricants Standardization and Approval Committee (ILSAC) recently adopted a Fired Engine Test for inclusion in the upcoming ILSAC GF-6 lubricant specification. The new test, developed by ILSAC member Ford Motor Co., uses a 2.0L GTDI Eco Boost engine to evaluate the impact of oil quality on wear performance by measuring the length of the timing chain over time.

MOTOR: How did Infineum approach this challenge?

The two most common timing chains used in vehicle today are silent and roller timing chains.

Reith: Engine oils contain additives that can limit surface degradation. Infineon conducted experiments to better understand timing chain wear and to assess the impact of alternative lubricant formulations on the two most common types of timing chains used today. These are:

  • Silent chains are constructed using metal links, which are held in place by cylindrical pins. This type of chain is featured in the Ford engine that was used in the development of the ILSAC GF-6 Chain Wear Test. Silent chains have many design advantages, including simplicity, lower cost and low chain noise.
  • Roller chains are more complex and expensive than silent chains. Roller chains, designed to reduce friction, feature link pins reinforced by a roller support (or bushing) that accommodates freely rotating steel rollers. However, this type has several disadvantages: They are more expensive to manufacture, wear more rapidly if particles become trapped and produce significant chain noise.

Wear analysis helps automakers and lubricant manufacturers assess and improve timing chain hardware, surface coatings and lubricant formulations. This image shows wear scars left by different qualities of engine oil.

MOTOR: What other factors affect timing chain wear?

Reith: The construction of the chain contact points directly affected chain wear. Over extended periods of routine use, timing chains wear and slack develops between surfaces that are in immediate contact. This slack causes the chain to elongate and changes its pitch through the relative displacement of the links. We observed wear in the rollers and supports on a roller chain and in the pivot pins and links of a silent chain. Chain wear can also be promoted by various mechanisms including the repeated pivoting motion of driving links or bushings against stationary connector pins, the presence of excessive amounts of soot and/or acid and the relationship to other timing components. In addition, the lubrication regime is not constant; engine operating conditions and oil viscosity are not fixed. Hence, the wear rate varies.

MOTOR: What analysis techniques does Infineon use to observe and assess wear?

Reith: Infineon employed a variety of advanced scientific techniques to examine the surfaces of chains to better understand the impacts. Other techniques were then used to evaluate the pins and links in the deconstructed timing chain. For instance, we used a 3D profilometer for wear-mapping to pinpoint the areas of damage in multiple parts of the chain. We also used scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) to analyze the surfaces of chains.

This image shows how time can impact surface wear using good vs. poor quality engine oil.

MOTOR: Where does timing chain wear show up?

Reith: Together the techniques enabled us to zero in more exactly where and how timing chain wear was occurring. For instance, we used two oils — a relatively good and a poor performing oil — which were run on the same ILSAC GF-6 Fired Engine Test stand for different time durations. While the results were consistent with the chain stretch results obtained from the ILSAC GF-6 fired engine test, we found some specific areas lubricant manufacturers could focus on:

  • Scar depth along the length of individual pins — When comparing the wear scar results for the two test oils, deeper wear scars were observed on the pins for samples from longer tests using lower quality oil.
  • Surface planarity for individual links — SEM and EDS microscopy were used to analyze defects on the surfaces of chains in an effort to characterize them as being a result of scratching, etching, pitting or polishing. The location, type, and extent of distress provide a better understanding of possible wear mechanisms.
  • Deformation near holes potentially caused by motion against the pins — For the two test oils, test duration and oil quality were observed to have an impact on the removal of machining marks, perpendicular to the direction of pivoting motion, in the holes of the links. In addition, the onset of polishing was noted.

MOTOR: Are there other resources Infineum uses to test and observe wear?

Reith: Infineum designed and developed a Motored Screener Rig to isolate the operational variables that might promote wear, and to screen experimental oils easily and quickly. The configuration and dimensions of the rig match the timing chain system in the engine featured in the ILSAC GF-6 Chain Wear Test. However, it is much easier to customize cam loadings, engine speed, oil pressure, and oil temperature for each rig test. In addition, the test duration for the rig has so far been much shorter than for the Fired Engine Tests, which allows an increased sample throughput. Like the ILSAC GF-6 tests, the rig is also able to discriminate between oils of varying quality. But with the rig environment, operating conditions that significantly influence wear rate can be more readily observed.

Watch this video for a closer look at how viscosity modifiers can deliver technologically advanced lubricant formulations. (Video — Infineum International Ltd.)

MOTOR: Where do you see future R&D headed?

Reith: Infineum is committed to furthering the understanding of timing chain degradation under various operating conditions. Future work is expected to focus on extending the scope of existing studies by assessing the extent of regional hardware variations and mapping the relationship of wear to engine operating conditions and surface chemistry. Because OEMs around the globe use different timing chains in their engines, the rig may, in certain circumstances, be a useful tool to help mimic specific hardware and operating conditions, both currently used or under development. In addition, test conditions can be varied to pinpoint the most impactful variables and to allow the faster identification of poor and good performing oils.

MOTOR: What practical implications does your R&D have for the service repair industry?

Reith: By using wear-mapping, SEM and EDS techniques to analyze the aged chains after the Fired Engine Test, we were able to quantify elemental compositions at targeted surface locations. These results will help us assess the effectiveness of formulations and to evaluate the base metallurgy for evidence of surface coatings, which will provide information about surface treatments for new timing chain hardware. In addition, we found evidence of tribofilm on the links, which will point the way toward improved lubricant formulations.

[Editor's note: Visit MOTOR for the latest diagnostic and service insights.]

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