Ccmano
03-08-2009, 09:44 PM
During our recent get together the issue of cam wear, oil and ZDP (Zinc/Phosphate) came up. As most of us are aware this issue has been discussed many times and is of special interest to LT5 owners with our flat tappet valve trains. "Corvette Enthusiast Magazine" recently ran a series of articles on this subject written by Hib Halverson that are in my opinion the most complete and well researched on the subject that I have ever read. Now that these issues of the magazine are off the shelves I thought it might enlightening to share this information and invite further discussion. I have transcribed the first acticle below. The second will follow.
H
:cheers:
"In the August '08 issue of HE, we published an article on lubricants. That generated a lot of feedback, especially the part on engine oil, so back by popular demand, but more in depth, is Corvette Enthusiast's coverage of engine oil. For several years, Corvetters have read and heard rumors, discussions, arguments, fairy tales and even a few facts about accelerated wear of flat tappet camshafts and lifters in overhead valve engines. Allegedly, engine oil has a key role in this problem. In this two-part series, we'll examine the problem, its severity and how can it be solved.
VALVE TRAIN BASICS: From 1953 until 1986, production Corvette engines had flat tappet cams. Since then, with one exception,they have used roller tappets. The exception was the LT5 in 1990-95 ZR-1s, but ifs only peripherally related to this wear issue,because it had overhead cams and direct acting, bucket-type, flat tappets. While flat tappets haven't been in stock for overhead valve (OHV) Corvette engines for over 20 years, they are still available from aftermarket, high-performance camshaft vendors, mainly because of their lower cost. They are also available as original equipment (OE) replacements.
Lastly, there are a hundred thousand or so unrestored '53-'86s with original valve trains. Executive summary: many flat tappet engines are still on the road, today. In an OHV engine during valve opening, the camshaft lobe pushes the tappet - some call it a "lifter" or a "follower"- against valve spring pressure multiplied by the rocker arm ratio. After Oldsmobile pioneered high-rpm OHV engines in the early 1950s, higher valve spring pressure to extend engine speed range became common, in spite of the OHV design's high valvetrain mass. The combination of spring pressure, rocker ratio and inertia makes for a high load,concentrated on a small, elliptically-shaped area where the lobe and tappet make contact The area of highest load surrounds a point where what valvetrain
engineers call the "minimum radius of curvature" or "nose radius" intersects the lobe surface. Imagine the nose of the cam lobe as a series of segments of circumferences of varying radii, the shortest of which is a line from the lobe surface to the center of the circle closest to that surface. This point is at, or in the case of asymmetrical lobe profiles, near maximum lift. Since the lobe slides or scrapes across the tappet face and both are under high load; that contact area has the potential for high rates of wear. In a stock Corvette flat tappet engine, pressure near maximum lift can be up to about 180,000 psi, a number that our research indicates was GM's "general rule" for maximum lobe/lifter interface pressure in production flat tappet engines. That number goes back many years, perhaps as far as the mid-to-late 1950s. It is still valid today for the part of engine oil certification tests which validates durability of flat tappet valve trains. In engines having aftermarket, highperformance cams, higher-tension valve springs and/or higher-ratio
rocker arms, the pressure will be more - upwards of 200.000 psi. All-out racing, flat tappet valve trains are around 250,000 psi., or 5 tons per square inch, and a few, such as in NASCAR Sprint Cup engines, can be closer to 300,000 psi. How much is that? Imagine a Boeing 757 jetliner sitting on a postage stamp. As incredible as that might seem, both Chase Knight of e Cams and Billy Godbold of Comp told us that the dynamic loads are higher because valvetrain motion violent and complex. "If you just rotate by hand, the cam/tappet interface will see the highest mad at the nose," Godbold told us. However, as rpm increases, average load goes down, but you get surge (load fluctuations) with the spring coils running into each other. Even at moderate rpm, «you'll get coil-to-coil interaction. Any dynamics model which doesn't include that will be in error. "This interaction is not coil bind. The valvespring wire vibrates and touches other coils. It starts a wave though the system like*£ thumping a slinky. Depending on the Springs frequency, this wave may go to the last coil, then reflect back hitting the •retainer with force opposite the direction *e retainer is moving. Retainer movement combined with force applied in the opposite (direction creates very high loads. "At low rpm, the spring might surge five times. At high rpm, it might surge once, then do what I call 'McDonalding'- the valvetrain lofts (the tappet is thrown off the lobe) then smacks the nose and bounces a second time. It looks like two arches. The loads are tremendous - four or five times the open pressure. Trying to see this as a static system doesn't work with aftermarket performance cams." Godbold continues. "The only ways you get the dynamic load is to computer model valve train motion or measure it. Those loads are so much higher than
static loads, it's not even funny.
"MANAGING WEAR: Three strategies mitigate wear of cam lobes and lifter faces. The first is mechanical engineering. Flat tappets...well, they're not flat. Their faces are slightly convex or "crowned". In addition, the lobe's longitudinal profile has a very slight taper, usually .0012 to .0020-inch, and finally, the lifter axis is offset from the plane bisecting the lobe face. In combination, these features cause the lifter to rotate as the cam lobe rubs across its face. That eliminates the lobe contact point dwelling in the same place on the lifter face, causing high levels of wear. The second anti-wear strategy is technology. Over time, better camshaft and lifter materials have been developed. This is not to say that every camshaft and lifter manufacturer uses those better materials, but they do exist and have been implemented by OEs and some aftermarket companies. Additionally, surface treatments that are more robust and more permanent than phosphating, which dates to the mid-'50s, have been developed by the aftermarket such as
nitriding, and most recently, Crane Cams' Mikronite process. Lastly, more stringent quality controls have also improved durability.
The third strategy is better lubrication. For over half a century, "extreme pressure" or "EP" lubricants have been added to engine oil to
extend camshaft/lifter durability. They enhance the oil's ability to lubricate parts which rub against a small area of each other and are under high load while they rub. In the early '50s, following introduction of higher valve spring pressures, there were problems with valve train wear. In response, car companies introduced camshafts with a sacrificial phosphate coating which enhanced break-in reliability and lifters made of hardenable alloys of cast iron. They also pressured the oil industry to reformulate engine oils to improve cam and lifter durability. Its response was a significant increase of EP additives in oil blends. Mechanical properties, materials and lubrication can also increase wear. If a lobe is not properly tapered or alifter face is not manufactured with the proper convex profile or surface finish, rapid wear will occur. If the materials are substandard (poor quality iron) or the surface is not treated properly (poorquality phosphating of the cam), the cam and lifters will fail. If the engine oil lacks a proper EP additive package
(and this can be either too little, or sometimes, too much), the valve train may suffer poor durability.
WHY ZDP GETS SO MUCH ATTENTION: The most common EP additive in automotive engine oils is zinc dialkyldithiophosphate (ZDDP), a family of coordination compounds of zinc and dithiophosphoric acid which, in longerchain, molecular derivatives, easily dissolve in engine oils. Known more commonly as "zinc dithiophosphate" (ZDP), "zinc phosphate", or quite incorrectly, just "zinc", this compound was initially added to oil in the 1940s as an anticorrosive/antioxidant. Later, it was discovered to be an excellent extreme pressure lubricant. When subjected to heat present at the lobe/lifter interface, ZDP decomposes into alcohol, zinc, sulfur and phosphorous. The alcohol evaporates and the zinc mostly washes away, leaving sulfur and phosphorous to combine with iron molecules on the surface of the cam lobe to make iron sulfide and iron phosphate, the two compounds which perform EP lubrication. "The'di-thio'in'zincdithiophosphate' means for every phosphorous there are two sulfur molecules," Red Line Synthetic Oil Corporation's
Vice President and top petrochemical engineer, Roy Howell, told Corvette Enthusiast. "Sulfur is probably more important than zinc and phosphorous. "The (cam and lifter) wear surfaces are rich in iron and sulfur with a lesser amount of phosphorous. The ZDP decomposes into a soft, thin film of iron sulfide and iron phosphate which prevents iron adhesion, or welding. The zinc doesn't do much. If you look at photomicrographs of cams and lifters, there's hardly any zinc coating, but there's a lot of iron sulfide coating and some iron phosphate coating. "With this process, you trade adhesive wear for chemical wear. If you didn't have these soft films, which prevent iron from touching iron - if you didn't have something in the middle, then you'd get adhesive wear - welding - and that iron to- iron weld would pull 'chunks' out of the lobe and follower. ...What makes zinc dialkyldithiophosphate unique is its precise thermal decomposition temperature which can be manipulated by changing the composition of the organic (alkyl) group attached to the phosphorous. If it decomposes at too low a temperature, chemical wear would occur where it is not needed, but if it
occurred at a higher temperature, then some adhesion or welding, would already be taking place... "There are a lot of different sulfur compounds," Howell continued, "but this one has 'precision-controlled' decomposition. In many of the others, the sulfur and the phosphorous are much more loosely bonded. There's a bigger 'range'. It might partially decompose at a lower temperature and finish at a higher temperature, or maybe decompose only at a higher temperature. However, with ZDP-boom at 400° F, it starts to thermally decompose, then react (with the surface of the lobe and lifter) to form those almost monomolecular soft films. As the lobe rubs against the follower, that film will get rubbed off, and in the next revolution, the same thing happens again." ZDP is slowly depleted by decomposition and evaporation, so eventually, EP lubrication becomes inadequate. This is one reason oilsneed to be changed periodically. While some petrochemical engineers consider sulfur of primary importance and some consumers misunderstand zinc content as benchmarking EP additives in oil, in reality, it is the phosphorous component about which the oil industry is most concerned. Oil blending data prior to the early '90s is difficult to acquire, but our research revealed that mass-marketed engine oil typically used by consumers from the late 1950s to the mid-'70s had enough ZDP to result in around 800 parts per million phosphorous content or "phos" as some engineers say. In the early '70s, "finger followers" were introduced in some single overhead camshaft (SOHC) engines. They presented a durability problem, initially thought to be caused by insufficient EP lubrication. In response, from the late '70s to the mid-1980s, phosphorus in most oils climbed to about 1000 ppm. Ironically, as experience with finger follower engines grew, it was eventually determined that, due to the location of the valvetrain in theengine, blowby-driven corrosion was affecting the durability problem more than insufficient EP lubrication. In the late 80s/early 90s, the oil industry began to decrease phosphorous, back towards 800 ppm because: 1) extra ZDP for finger followers proved unnecessary and alternative methods- improved materials, other additives - were found to enhance durability, 2) OEs were converting to roller lifters which required less EP lubrication, 3) OEs wanted to improve the longevity of emissions controls and 4) historically, as far back as the mid-'50s, 800 ppm phosphorous provided good durability offlat tappet cams and lifters in production OHV engines.
BACKING OFF THE CATALYST KILLER: Inevitably, the Federal government began to "stir the pot." By the late '80s, the Federal Environmental Protection Agency (EPA) decided that phosphorous released by small quantities of oil burned by the engine gradually deactivates or "poisons" the reactant which enables a catalytic converter (some call them "catalysts" or just "cats") to convert certain exhaust gas components to less toxi substances. Once that happens, the cat ceases to be effective. The EPA, deciding it was better for us to have expensive, long-life cats instead of more frequent replacements of "short-life" cats, offered car companies incentives for implementation of more durable catalysts. Politicians and EPA's mandarins figured the OEs would pressure the oil industry to scale back use of ZDP, thereby reducing phosphorous and preventing the premature demise of hundreds of millions of catalytic converters. This was a slow ramp-up, starting around the '80s at 50,000 miles. The current cat life requirement is 120,000 miles, and it goes to 150,000 miles for model year 2009. Sure enough, car companies, which by the mid-'90s expected to be using
either roller lifters in OHV engines or less highly-loaded, direct-acting flat tappets in OHC engines, convinced big oil to reduce phosphorous to extend cat life. Its leverage was the purchase of millions of gallons of oil a year to factory-fill their engines and its recommending types of oils in owner's manuals. In 1987, American car companies, along with Japanese manufacturers assembling cars in the U.S., formed the International Lubricant Standards and Approval Committee (ILSAC). One of ILSAC's goals was to enact standards which would gradually reduce phosphorous in engine oils carrying its and API's Service certifications. In 2002, to improve the standards process, ILSAC, the oil industry and the additive makers formed the ILSAC/Oil committee. "Basically, it's worked out within that committee, from the OEM, the oil and the additive sides, what new oil specs will be," current ILSAC/Oil Chairman, Robert Olree told us in an interview. "My job, as chairman, is 'o keep all those cats...you've heardof herding cats...keep those guys in line and make sure the process keeps noving forward."Herding cats, indeed! Imagine those meetings - all three groups with different
goals, agendas and strategies. Heck, we can't understand why Mr. Olree wants the job at all. ILSAC GF-1 ("GF" meaning "gasoline fueled") became effective in 1992. API •"ol lowed with an "SH" version of its Service" grades, which until recently, were more familiar to consumers. GF-1 was the first oil standard with a phosphorous ceiling - 1200 parts-per- million (ppm). API Service SF and prior, didn't regulate phosphorous. This first "max-phos" number was irrelevant, because other than racing, diesel and other special purpose engine oils that were not certified anyway, most oil bought by Vette owners had way less than 1200 ppm phosphorous. Nevertheless, the seemingly-pointless spec was purposeful. "The first time we limited phosphorous, it was 0.12%," Olree told us. "The oil industry doesn't like restrictions, so we put it in at .12 just to get the idea in place. It wasn't affecting anybody because no one was above that. Later, we started ratcheting the phos down." While GF-1 allowed up to 1200 ppm phosphorous, few of the GF-1 5W30s or 10W30s Corvetters used back then had more than 1000 ppm. So-called"racing oils" held phos to 1100-1300ppm. Most oils purchased by consumers ranged 800-1000 with a majority around 800, a figure which nearly half a century of research and experience proved was adequate to lubricate the vast majority of stock engines with flat tappet or finger follower valve trains and even some with mild, aftermarket, highperformance cams. Oils with viscosity higher than 10W30 were exempt from the phos limit. In 1996, GF-2 was issued, and in 2002, ILSAC/Oil released GF-3. API Service SJ is comparable to GF-2, and SL corresponds to GF-3. All of these mandated 1000 ppm max phos, but by then, most engine oils with viscosities 10W30 or less were about 800, with perhaps a few during the GF-3 period, getting down between 600 and 800 ppm. Viscosities higher than 10W30 continued exempt from the phosphorous limit. Where decreasing ZDP content first caused trouble was with engines havingaftermarket, flat tappet camshafts with aggressive profiles, racing valve springs or high-ratio rockers - parts which raise load at the lifter/lobe interface to over 200,000 psi. Such valvetrains required break-in procedures incorporating special additives, such as Crane Cams' "Superlube" or Red Line's "Engine Oil Break-In Additive," both of which have additional ZDP, along with other components, such as molybdenum disulfide. Once break-in was complete, these engines needed oil with 1000-1200 ppm phosphorous. As we will learn in Part 2, not all users of these cams were aware of this need, and some who were aware, long as oil companies disregarded it. With GF-1 through GF-3 and SJ to SL, phosphorous regulation was a maximum limit, not a minimum requirement. As didn't exceed that, they could put any percentage of ZDP in the oil necessary for it to pass the battery of tests required for certification. GF-4 came in 2005 and was matched by API Service SM. GF-4 required oils with viscosities of 10W30 or lower to hold phos above 600 ppm, but below 800 ppm. This was the first specification which drove any significant change in oil blends, because previously, most had been at
800-1000 ppm, at or below any prior phosphorous ceiling and now, phos was held in a range. Viscosities higher than 10W30 continued to exempt from phos limits. GF-5, due for introduction for the 2011 model year is not yet finalized, but ILSAC/Oil Chairman Olree, told Corvette Enthusiast that he believes GF-5 will have the same phosphorous specification as GF-4.
VALIDATING DURABILITY: For 50 years, American Society for Testing and Materials' (ATSM) "Sequence III Engine Oil Certification Tests" have been used to validate an oil's ability to properly lubricate production flat tappet cams. For about the last decade, Sequence III has been performed with a GeneralMotors 3800 Series II V-6. Since all 3800s have roller lifters, the test engines are retrofitted with flat tappet camsand valve spring pressure of about 205 pounds open or, with the 3800's 1.67:1 rocker ratio, 328 Ibs at the lifter. While that spring pressure is not overly high by V-8 standards, it is higher than stock for a 3800. Additionally, the V-6's camshaft base circle is smaller and that further increases load at the lobe/lifter interface beyond what a V-8 would sustain from the same spring pressure. These measures were taken to increase load at the lobe/lifter interface to 180,000 psi. SAE's Technical Paper
How Much ZDP is Enough describes the test's operating conditions as, "... designed to simulate a flat tappet, OHV pushrod engine in a pickup truck pulling a loaded cattle trailer across the desert on a hot day."The current version, IMG, optional for GF-3 and required for GF-4 certification, specifies that the engine run at 3600 rpm and be loaded such that its output is about 80% of its rated torque. It is run with 95° intake air temperature, 239°F coolant temperature and 302°F oil temperature. The test lasts for 100 hours with brief stops every 20 hours to check oil level. After the test, the engine is disassembled, and the cam and lifters are precisely measured for wear. Regardless of any fairy tales one reads on the Internet or in magazines, the Sequence NIC test is brutal - more severe than the IIIF and HIE sequences that proceeded it and far more severe than any tests of flat tappet cam/lifter
wear to which any engine oils for use in gasoline engines of any period prior to 1993 were subjected. That said, there are a couple of
limitations of Sequence IHG: 1) it doesn't take into account aftermarket camswhich received phosphate coatings of a lesser quality than was typical of OE cams from the mid-'50s until 1986 and 2) it's not relevant to valvetrains with loads higher than stock.
AND FINALLY: If you haven't picked up on it yet, there is an urban legend in the car hobby which has been widely repeated by word-of-mouth, on the Internet, and to a lesser extent, in magazines - one time, even in this one, that zinc dithiosphate ("ZDP", "ZDDP", "zinc", etc.) has been "eliminated" from today's engine oils. The reality is: ZDP remains in all engine oils marketed for use in gasoline and diesel engines in ground vehicles and will continue to foe in them for the foreseeable future.
In Part 2, we'll look more at how changes in engine oil affect Corvette engines. We'll discuss various strategies to solve problems created by those changes. We'll talk about flat tappet camshaft installation and break-in procedure. Finally, we'll review specific oil choices for yourVette.
RESEARCH FOR THIS STORY:
interviews with engineers at oil companies, aftermarket cam manufacturers and General Motors Powertrain along with World Wide Web
searches, information from oil refiners and the American Petroleum Institute (API), and finally, three Society of Automotive Engineers (SAE) TechnicalPapers: Antiwear Performance of Low Phosphorous Engine Oils on TappetInsets in Motored Sliding Valvetrain Test, («2003-01-3119); How Much ZDP is Enough, (#2004-01-2986) and Development of the Sequence IIIC Engine Oil Certification Test (#2004-01-2987). Corvette Enthusiast would like to thank the following for special assistance during the research for this article: Roy Howell, Vice Presidentand Chief Engineer, Red Line Synthetic Oil Corporation; Chase Knight, Valvetrain Products Manager, Crane Cams; Billy Godbold, Cam Design Research and Development Engineer, Comp Cams; Robert M. Olreeheard ofmoving, Fuels and Lubricants Manager, General Motors Powertrain and Chairman, Oil Committee, International Lubricant Standards and Approval Committee; Tim Wusz, Director of Engineering, Rockett Brand Racing Fuels and former petrochemical engineer for 76 Performance Products; Karen Ktardich, Media Relations Manager, Society of Automotive Engineers; Mark DeGroff, Mark DeGroff's Cylinder Head Service and Machine Shop; Graham Behan, Chief Engineer, Lingenfelter Performance Engineering and former LT5 Engine Release Engineer, Lotus Engineering; Barry Branson, Valvoline Brand Specialist, Communications and Corporate Avalve trainsffairs Section, Ashland, Inc.: Jim VanDorn, General Manager, AutoMasters of Bovalve trainswling Green, Inc."
H
:cheers:
"In the August '08 issue of HE, we published an article on lubricants. That generated a lot of feedback, especially the part on engine oil, so back by popular demand, but more in depth, is Corvette Enthusiast's coverage of engine oil. For several years, Corvetters have read and heard rumors, discussions, arguments, fairy tales and even a few facts about accelerated wear of flat tappet camshafts and lifters in overhead valve engines. Allegedly, engine oil has a key role in this problem. In this two-part series, we'll examine the problem, its severity and how can it be solved.
VALVE TRAIN BASICS: From 1953 until 1986, production Corvette engines had flat tappet cams. Since then, with one exception,they have used roller tappets. The exception was the LT5 in 1990-95 ZR-1s, but ifs only peripherally related to this wear issue,because it had overhead cams and direct acting, bucket-type, flat tappets. While flat tappets haven't been in stock for overhead valve (OHV) Corvette engines for over 20 years, they are still available from aftermarket, high-performance camshaft vendors, mainly because of their lower cost. They are also available as original equipment (OE) replacements.
Lastly, there are a hundred thousand or so unrestored '53-'86s with original valve trains. Executive summary: many flat tappet engines are still on the road, today. In an OHV engine during valve opening, the camshaft lobe pushes the tappet - some call it a "lifter" or a "follower"- against valve spring pressure multiplied by the rocker arm ratio. After Oldsmobile pioneered high-rpm OHV engines in the early 1950s, higher valve spring pressure to extend engine speed range became common, in spite of the OHV design's high valvetrain mass. The combination of spring pressure, rocker ratio and inertia makes for a high load,concentrated on a small, elliptically-shaped area where the lobe and tappet make contact The area of highest load surrounds a point where what valvetrain
engineers call the "minimum radius of curvature" or "nose radius" intersects the lobe surface. Imagine the nose of the cam lobe as a series of segments of circumferences of varying radii, the shortest of which is a line from the lobe surface to the center of the circle closest to that surface. This point is at, or in the case of asymmetrical lobe profiles, near maximum lift. Since the lobe slides or scrapes across the tappet face and both are under high load; that contact area has the potential for high rates of wear. In a stock Corvette flat tappet engine, pressure near maximum lift can be up to about 180,000 psi, a number that our research indicates was GM's "general rule" for maximum lobe/lifter interface pressure in production flat tappet engines. That number goes back many years, perhaps as far as the mid-to-late 1950s. It is still valid today for the part of engine oil certification tests which validates durability of flat tappet valve trains. In engines having aftermarket, highperformance cams, higher-tension valve springs and/or higher-ratio
rocker arms, the pressure will be more - upwards of 200.000 psi. All-out racing, flat tappet valve trains are around 250,000 psi., or 5 tons per square inch, and a few, such as in NASCAR Sprint Cup engines, can be closer to 300,000 psi. How much is that? Imagine a Boeing 757 jetliner sitting on a postage stamp. As incredible as that might seem, both Chase Knight of e Cams and Billy Godbold of Comp told us that the dynamic loads are higher because valvetrain motion violent and complex. "If you just rotate by hand, the cam/tappet interface will see the highest mad at the nose," Godbold told us. However, as rpm increases, average load goes down, but you get surge (load fluctuations) with the spring coils running into each other. Even at moderate rpm, «you'll get coil-to-coil interaction. Any dynamics model which doesn't include that will be in error. "This interaction is not coil bind. The valvespring wire vibrates and touches other coils. It starts a wave though the system like*£ thumping a slinky. Depending on the Springs frequency, this wave may go to the last coil, then reflect back hitting the •retainer with force opposite the direction *e retainer is moving. Retainer movement combined with force applied in the opposite (direction creates very high loads. "At low rpm, the spring might surge five times. At high rpm, it might surge once, then do what I call 'McDonalding'- the valvetrain lofts (the tappet is thrown off the lobe) then smacks the nose and bounces a second time. It looks like two arches. The loads are tremendous - four or five times the open pressure. Trying to see this as a static system doesn't work with aftermarket performance cams." Godbold continues. "The only ways you get the dynamic load is to computer model valve train motion or measure it. Those loads are so much higher than
static loads, it's not even funny.
"MANAGING WEAR: Three strategies mitigate wear of cam lobes and lifter faces. The first is mechanical engineering. Flat tappets...well, they're not flat. Their faces are slightly convex or "crowned". In addition, the lobe's longitudinal profile has a very slight taper, usually .0012 to .0020-inch, and finally, the lifter axis is offset from the plane bisecting the lobe face. In combination, these features cause the lifter to rotate as the cam lobe rubs across its face. That eliminates the lobe contact point dwelling in the same place on the lifter face, causing high levels of wear. The second anti-wear strategy is technology. Over time, better camshaft and lifter materials have been developed. This is not to say that every camshaft and lifter manufacturer uses those better materials, but they do exist and have been implemented by OEs and some aftermarket companies. Additionally, surface treatments that are more robust and more permanent than phosphating, which dates to the mid-'50s, have been developed by the aftermarket such as
nitriding, and most recently, Crane Cams' Mikronite process. Lastly, more stringent quality controls have also improved durability.
The third strategy is better lubrication. For over half a century, "extreme pressure" or "EP" lubricants have been added to engine oil to
extend camshaft/lifter durability. They enhance the oil's ability to lubricate parts which rub against a small area of each other and are under high load while they rub. In the early '50s, following introduction of higher valve spring pressures, there were problems with valve train wear. In response, car companies introduced camshafts with a sacrificial phosphate coating which enhanced break-in reliability and lifters made of hardenable alloys of cast iron. They also pressured the oil industry to reformulate engine oils to improve cam and lifter durability. Its response was a significant increase of EP additives in oil blends. Mechanical properties, materials and lubrication can also increase wear. If a lobe is not properly tapered or alifter face is not manufactured with the proper convex profile or surface finish, rapid wear will occur. If the materials are substandard (poor quality iron) or the surface is not treated properly (poorquality phosphating of the cam), the cam and lifters will fail. If the engine oil lacks a proper EP additive package
(and this can be either too little, or sometimes, too much), the valve train may suffer poor durability.
WHY ZDP GETS SO MUCH ATTENTION: The most common EP additive in automotive engine oils is zinc dialkyldithiophosphate (ZDDP), a family of coordination compounds of zinc and dithiophosphoric acid which, in longerchain, molecular derivatives, easily dissolve in engine oils. Known more commonly as "zinc dithiophosphate" (ZDP), "zinc phosphate", or quite incorrectly, just "zinc", this compound was initially added to oil in the 1940s as an anticorrosive/antioxidant. Later, it was discovered to be an excellent extreme pressure lubricant. When subjected to heat present at the lobe/lifter interface, ZDP decomposes into alcohol, zinc, sulfur and phosphorous. The alcohol evaporates and the zinc mostly washes away, leaving sulfur and phosphorous to combine with iron molecules on the surface of the cam lobe to make iron sulfide and iron phosphate, the two compounds which perform EP lubrication. "The'di-thio'in'zincdithiophosphate' means for every phosphorous there are two sulfur molecules," Red Line Synthetic Oil Corporation's
Vice President and top petrochemical engineer, Roy Howell, told Corvette Enthusiast. "Sulfur is probably more important than zinc and phosphorous. "The (cam and lifter) wear surfaces are rich in iron and sulfur with a lesser amount of phosphorous. The ZDP decomposes into a soft, thin film of iron sulfide and iron phosphate which prevents iron adhesion, or welding. The zinc doesn't do much. If you look at photomicrographs of cams and lifters, there's hardly any zinc coating, but there's a lot of iron sulfide coating and some iron phosphate coating. "With this process, you trade adhesive wear for chemical wear. If you didn't have these soft films, which prevent iron from touching iron - if you didn't have something in the middle, then you'd get adhesive wear - welding - and that iron to- iron weld would pull 'chunks' out of the lobe and follower. ...What makes zinc dialkyldithiophosphate unique is its precise thermal decomposition temperature which can be manipulated by changing the composition of the organic (alkyl) group attached to the phosphorous. If it decomposes at too low a temperature, chemical wear would occur where it is not needed, but if it
occurred at a higher temperature, then some adhesion or welding, would already be taking place... "There are a lot of different sulfur compounds," Howell continued, "but this one has 'precision-controlled' decomposition. In many of the others, the sulfur and the phosphorous are much more loosely bonded. There's a bigger 'range'. It might partially decompose at a lower temperature and finish at a higher temperature, or maybe decompose only at a higher temperature. However, with ZDP-boom at 400° F, it starts to thermally decompose, then react (with the surface of the lobe and lifter) to form those almost monomolecular soft films. As the lobe rubs against the follower, that film will get rubbed off, and in the next revolution, the same thing happens again." ZDP is slowly depleted by decomposition and evaporation, so eventually, EP lubrication becomes inadequate. This is one reason oilsneed to be changed periodically. While some petrochemical engineers consider sulfur of primary importance and some consumers misunderstand zinc content as benchmarking EP additives in oil, in reality, it is the phosphorous component about which the oil industry is most concerned. Oil blending data prior to the early '90s is difficult to acquire, but our research revealed that mass-marketed engine oil typically used by consumers from the late 1950s to the mid-'70s had enough ZDP to result in around 800 parts per million phosphorous content or "phos" as some engineers say. In the early '70s, "finger followers" were introduced in some single overhead camshaft (SOHC) engines. They presented a durability problem, initially thought to be caused by insufficient EP lubrication. In response, from the late '70s to the mid-1980s, phosphorus in most oils climbed to about 1000 ppm. Ironically, as experience with finger follower engines grew, it was eventually determined that, due to the location of the valvetrain in theengine, blowby-driven corrosion was affecting the durability problem more than insufficient EP lubrication. In the late 80s/early 90s, the oil industry began to decrease phosphorous, back towards 800 ppm because: 1) extra ZDP for finger followers proved unnecessary and alternative methods- improved materials, other additives - were found to enhance durability, 2) OEs were converting to roller lifters which required less EP lubrication, 3) OEs wanted to improve the longevity of emissions controls and 4) historically, as far back as the mid-'50s, 800 ppm phosphorous provided good durability offlat tappet cams and lifters in production OHV engines.
BACKING OFF THE CATALYST KILLER: Inevitably, the Federal government began to "stir the pot." By the late '80s, the Federal Environmental Protection Agency (EPA) decided that phosphorous released by small quantities of oil burned by the engine gradually deactivates or "poisons" the reactant which enables a catalytic converter (some call them "catalysts" or just "cats") to convert certain exhaust gas components to less toxi substances. Once that happens, the cat ceases to be effective. The EPA, deciding it was better for us to have expensive, long-life cats instead of more frequent replacements of "short-life" cats, offered car companies incentives for implementation of more durable catalysts. Politicians and EPA's mandarins figured the OEs would pressure the oil industry to scale back use of ZDP, thereby reducing phosphorous and preventing the premature demise of hundreds of millions of catalytic converters. This was a slow ramp-up, starting around the '80s at 50,000 miles. The current cat life requirement is 120,000 miles, and it goes to 150,000 miles for model year 2009. Sure enough, car companies, which by the mid-'90s expected to be using
either roller lifters in OHV engines or less highly-loaded, direct-acting flat tappets in OHC engines, convinced big oil to reduce phosphorous to extend cat life. Its leverage was the purchase of millions of gallons of oil a year to factory-fill their engines and its recommending types of oils in owner's manuals. In 1987, American car companies, along with Japanese manufacturers assembling cars in the U.S., formed the International Lubricant Standards and Approval Committee (ILSAC). One of ILSAC's goals was to enact standards which would gradually reduce phosphorous in engine oils carrying its and API's Service certifications. In 2002, to improve the standards process, ILSAC, the oil industry and the additive makers formed the ILSAC/Oil committee. "Basically, it's worked out within that committee, from the OEM, the oil and the additive sides, what new oil specs will be," current ILSAC/Oil Chairman, Robert Olree told us in an interview. "My job, as chairman, is 'o keep all those cats...you've heardof herding cats...keep those guys in line and make sure the process keeps noving forward."Herding cats, indeed! Imagine those meetings - all three groups with different
goals, agendas and strategies. Heck, we can't understand why Mr. Olree wants the job at all. ILSAC GF-1 ("GF" meaning "gasoline fueled") became effective in 1992. API •"ol lowed with an "SH" version of its Service" grades, which until recently, were more familiar to consumers. GF-1 was the first oil standard with a phosphorous ceiling - 1200 parts-per- million (ppm). API Service SF and prior, didn't regulate phosphorous. This first "max-phos" number was irrelevant, because other than racing, diesel and other special purpose engine oils that were not certified anyway, most oil bought by Vette owners had way less than 1200 ppm phosphorous. Nevertheless, the seemingly-pointless spec was purposeful. "The first time we limited phosphorous, it was 0.12%," Olree told us. "The oil industry doesn't like restrictions, so we put it in at .12 just to get the idea in place. It wasn't affecting anybody because no one was above that. Later, we started ratcheting the phos down." While GF-1 allowed up to 1200 ppm phosphorous, few of the GF-1 5W30s or 10W30s Corvetters used back then had more than 1000 ppm. So-called"racing oils" held phos to 1100-1300ppm. Most oils purchased by consumers ranged 800-1000 with a majority around 800, a figure which nearly half a century of research and experience proved was adequate to lubricate the vast majority of stock engines with flat tappet or finger follower valve trains and even some with mild, aftermarket, highperformance cams. Oils with viscosity higher than 10W30 were exempt from the phos limit. In 1996, GF-2 was issued, and in 2002, ILSAC/Oil released GF-3. API Service SJ is comparable to GF-2, and SL corresponds to GF-3. All of these mandated 1000 ppm max phos, but by then, most engine oils with viscosities 10W30 or less were about 800, with perhaps a few during the GF-3 period, getting down between 600 and 800 ppm. Viscosities higher than 10W30 continued exempt from the phosphorous limit. Where decreasing ZDP content first caused trouble was with engines havingaftermarket, flat tappet camshafts with aggressive profiles, racing valve springs or high-ratio rockers - parts which raise load at the lifter/lobe interface to over 200,000 psi. Such valvetrains required break-in procedures incorporating special additives, such as Crane Cams' "Superlube" or Red Line's "Engine Oil Break-In Additive," both of which have additional ZDP, along with other components, such as molybdenum disulfide. Once break-in was complete, these engines needed oil with 1000-1200 ppm phosphorous. As we will learn in Part 2, not all users of these cams were aware of this need, and some who were aware, long as oil companies disregarded it. With GF-1 through GF-3 and SJ to SL, phosphorous regulation was a maximum limit, not a minimum requirement. As didn't exceed that, they could put any percentage of ZDP in the oil necessary for it to pass the battery of tests required for certification. GF-4 came in 2005 and was matched by API Service SM. GF-4 required oils with viscosities of 10W30 or lower to hold phos above 600 ppm, but below 800 ppm. This was the first specification which drove any significant change in oil blends, because previously, most had been at
800-1000 ppm, at or below any prior phosphorous ceiling and now, phos was held in a range. Viscosities higher than 10W30 continued to exempt from phos limits. GF-5, due for introduction for the 2011 model year is not yet finalized, but ILSAC/Oil Chairman Olree, told Corvette Enthusiast that he believes GF-5 will have the same phosphorous specification as GF-4.
VALIDATING DURABILITY: For 50 years, American Society for Testing and Materials' (ATSM) "Sequence III Engine Oil Certification Tests" have been used to validate an oil's ability to properly lubricate production flat tappet cams. For about the last decade, Sequence III has been performed with a GeneralMotors 3800 Series II V-6. Since all 3800s have roller lifters, the test engines are retrofitted with flat tappet camsand valve spring pressure of about 205 pounds open or, with the 3800's 1.67:1 rocker ratio, 328 Ibs at the lifter. While that spring pressure is not overly high by V-8 standards, it is higher than stock for a 3800. Additionally, the V-6's camshaft base circle is smaller and that further increases load at the lobe/lifter interface beyond what a V-8 would sustain from the same spring pressure. These measures were taken to increase load at the lobe/lifter interface to 180,000 psi. SAE's Technical Paper
How Much ZDP is Enough describes the test's operating conditions as, "... designed to simulate a flat tappet, OHV pushrod engine in a pickup truck pulling a loaded cattle trailer across the desert on a hot day."The current version, IMG, optional for GF-3 and required for GF-4 certification, specifies that the engine run at 3600 rpm and be loaded such that its output is about 80% of its rated torque. It is run with 95° intake air temperature, 239°F coolant temperature and 302°F oil temperature. The test lasts for 100 hours with brief stops every 20 hours to check oil level. After the test, the engine is disassembled, and the cam and lifters are precisely measured for wear. Regardless of any fairy tales one reads on the Internet or in magazines, the Sequence NIC test is brutal - more severe than the IIIF and HIE sequences that proceeded it and far more severe than any tests of flat tappet cam/lifter
wear to which any engine oils for use in gasoline engines of any period prior to 1993 were subjected. That said, there are a couple of
limitations of Sequence IHG: 1) it doesn't take into account aftermarket camswhich received phosphate coatings of a lesser quality than was typical of OE cams from the mid-'50s until 1986 and 2) it's not relevant to valvetrains with loads higher than stock.
AND FINALLY: If you haven't picked up on it yet, there is an urban legend in the car hobby which has been widely repeated by word-of-mouth, on the Internet, and to a lesser extent, in magazines - one time, even in this one, that zinc dithiosphate ("ZDP", "ZDDP", "zinc", etc.) has been "eliminated" from today's engine oils. The reality is: ZDP remains in all engine oils marketed for use in gasoline and diesel engines in ground vehicles and will continue to foe in them for the foreseeable future.
In Part 2, we'll look more at how changes in engine oil affect Corvette engines. We'll discuss various strategies to solve problems created by those changes. We'll talk about flat tappet camshaft installation and break-in procedure. Finally, we'll review specific oil choices for yourVette.
RESEARCH FOR THIS STORY:
interviews with engineers at oil companies, aftermarket cam manufacturers and General Motors Powertrain along with World Wide Web
searches, information from oil refiners and the American Petroleum Institute (API), and finally, three Society of Automotive Engineers (SAE) TechnicalPapers: Antiwear Performance of Low Phosphorous Engine Oils on TappetInsets in Motored Sliding Valvetrain Test, («2003-01-3119); How Much ZDP is Enough, (#2004-01-2986) and Development of the Sequence IIIC Engine Oil Certification Test (#2004-01-2987). Corvette Enthusiast would like to thank the following for special assistance during the research for this article: Roy Howell, Vice Presidentand Chief Engineer, Red Line Synthetic Oil Corporation; Chase Knight, Valvetrain Products Manager, Crane Cams; Billy Godbold, Cam Design Research and Development Engineer, Comp Cams; Robert M. Olreeheard ofmoving, Fuels and Lubricants Manager, General Motors Powertrain and Chairman, Oil Committee, International Lubricant Standards and Approval Committee; Tim Wusz, Director of Engineering, Rockett Brand Racing Fuels and former petrochemical engineer for 76 Performance Products; Karen Ktardich, Media Relations Manager, Society of Automotive Engineers; Mark DeGroff, Mark DeGroff's Cylinder Head Service and Machine Shop; Graham Behan, Chief Engineer, Lingenfelter Performance Engineering and former LT5 Engine Release Engineer, Lotus Engineering; Barry Branson, Valvoline Brand Specialist, Communications and Corporate Avalve trainsffairs Section, Ashland, Inc.: Jim VanDorn, General Manager, AutoMasters of Bovalve trainswling Green, Inc."