Correct oil for flat tappets

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This question comes often. I was about to reply to it, but the thread was locked because an infamous blog was mentioned.
Originally Posted by Mad_Max_Sam
I own several 'flat-tappet' hot rods, including my mighty Cummins 5.9 (solid cam), and so I've got a couple questions... I talked with the tech folks at Shell and they claim their Rotella T4, 5 and 6 all have the 'flat-tappet' package, so I've been running Shell Rotella T4 10W30 in my hot rods, ... Meanwhile...I am still trying to determine what to run in my Cummins ... I may have to resort to the expensive mail order oils like Amsoil... Would appreciate any thoughts/recommendations. Cheers - Sam
For a flat tappet, you need a thick base oil. Any CK-4 15W-40 is an excellent choice. It sounds like you have an oil-pan heater; so, you should be OK in Colorado. In properly certified modern oils, the ZDDP content (phosphorus level) does not matter whether it's a flat tappet or not. Amsoil HD ACD 10W-30/SAE 30 is a monograde (no viscosity-index improver) with a very thick base oil, and it would be an excellent choice as well, except for the price. Some 5W-40 HDEOs are halfway decent choices, with a moderately high base-oil viscosity, if you don't have an oil-pan heater or a block heater, but they won't be as good as a 15W-40 or the Amsoil HD ACD 10W-30/SAE 30. See my spreadsheet linked below for the base-oil viscosity. The base-oil viscosity is listed under the BO DV150 column (cP units). You want a high number. Estimated VII content and base-oil viscosity of selected oils
 
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Just buy any motorcycle rated oil in the viscosity you desire, they have to do gears as well as flat tappets at RPM's your car engines can only dream about. Rod
 
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With friction modifiers for wet clutches also. No. Not a good idea. Just curious. What are the valve spring pressures for these bikes you are referring to? Most automotive performance flat tappet cams have spring pressures in the neighborhood of 130 lbs Seat Pressure/300-325 lbs open.
 
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Originally Posted by PontiacHO
With friction modifiers for wet clutches also. No. Not a good idea.
I'm wondering what exactly you mean by this. Do you believe there is something specific in MC oil that will harm your car engine? I've never used MC oil in a car engine, but I sure don't think it would do any harm.
 
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Automotive gaskets and seals aren't designed to contain friction modifiers. Again back to flat tappet valve spring pressures in motorcycles... Are they like automotive pressures? It's odd though i assisted with the disassembly of an early 70s 650 Honda engine. It had roller tappet. Are bikes being built with flat tappet currently?
 
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Isn't it the automotive oils that contain the friction modifiers (labeled with energy conserving etc that the motorcycle manuals used to say to avoid)....the friction modifiers (like a 'big slug of moly' >200ppm)? and not the dedicated motorcycle oils....since the friction modifiers can interfere with wet-clutch operation?
 
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That's good advice however I admit that I usually don't what I'm talking about. VR-1 worked for 396 and multiple Ponyiac motors.
 
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Originally Posted by Gokhan
This question comes often. I was about to reply to it, but the thread was locked because an infamous blog was mentioned.
Originally Posted by Mad_Max_Sam
I own several 'flat-tappet' hot rods, including my mighty Cummins 5.9 (solid cam), and so I've got a couple questions... I talked with the tech folks at Shell and they claim their Rotella T4, 5 and 6 all have the 'flat-tappet' package, so I've been running Shell Rotella T4 10W30 in my hot rods, ... Meanwhile...I am still trying to determine what to run in my Cummins ... I may have to resort to the expensive mail order oils like Amsoil... Would appreciate any thoughts/recommendations. Cheers - Sam
For a flat tappet, you need a thick base oil. Any CK-4 15W-40 is an excellent choice. It sounds like you have an oil-pan heater; so, you should be OK in Colorado. In properly certified modern oils, the ZDDP content (phosphorus level) does not matter whether it's a flat tappet or not. Amsoil HD ACD 10W-30/SAE 30 is a monograde (no viscosity-index improver) with a very thick base oil, and it would be an excellent choice as well, except for the price. Some 5W-40 HDEOs are halfway decent choices, with a moderately high base-oil viscosity, if you don't have an oil-pan heater or a block heater, but they won't be as good as a 15W-40 or the Amsoil HD ACD 10W-30/SAE 30. See my spreadsheet linked below for the base-oil viscosity. The base-oil viscosity is listed under the BO DV150 column (cP units). You want a high number. Estimated VII content and base-oil viscosity of selected oils
I'm not buying the thick base oil argument. I've seen a lot of solid flat tappet drag engines, pushing the extremes of valvetrain stability/jerk, with 0w-10 and 0w-20 oil and no excessive wear at all.
 

SR5

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Originally Posted by ragtoplvr
Just buy any motorcycle rated oil in the viscosity you desire
Yes this should work. PontiacHO, with MC oils they contain No friction modifiers (FM) as this could cause a wet clutch to slip. Resource Conserving (RC) car oils often do contain FM to improve fuel economy. So the problem is running a RC car oil in a bike, not the other way around. Here is a link to a Castrol 10W40 semi-synthetic motorcycle oil, it has Moly 50ppm, Boron 60ppm and Zinc 1000 ppm with a TBN of 9.3 https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/5343919/ The high zinc (ZDDP) is due to the engine oil also being the gear box oil in a shared sump motorcycle, so extra wear protection is required for the gears. Also this is a high shear environment so high shear resistant viscosity index improvers (VII) are used. Motorcycle oils are definitely high performance oils. Having said that, something like VR-1 is also a good oil, and most diesel HDEO's (like Rotella or Delo) have historically worked well too. Just agreeing that there are a few options out there for you, including MC oils.
 
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Any wear on a flat tappet drag engine valvetrain probably has very little to do with oil.... Now on a car that sees more than a few hours before rebuild, and NOT 200# valve springs and 9000rpm....probably a lot more so.
 

Gokhan

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Originally Posted by tundraotto
Any wear on a flat tappet drag engine valvetrain probably has very little to do with oil.... Now on a car that sees more than a few hours before rebuild, and NOT 200# valve springs and 9000rpm....probably a lot more so.
thumbsup
 
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Originally Posted by tundraotto
Any wear on a flat tappet drag engine valvetrain probably has very little to do with oil.... Now on a car that sees more than a few hours before rebuild, and NOT 200# valve springs and 9000rpm....probably a lot more so.
These engines have 8-10 years on them and participate in drag week every year. They've got a lot of runs and hours on them. I've seen plenty of flat tappet cam failures using 10w-30 and SAE 30 oils with insufficient ZDDP for the application. Enlighten me how the starting base oil impacts a part of the engine that operates in boundary lubrication. Why would it care? If that was the case, we'd just run aviation oils.
 
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8-10 years...and probably 5 hours of running time....get real. ZDDP is there for when the oil film strength has disappeared - like 9000rpm and 200lbs valve springs. Like said - comparing flat tappet drag racing motor to a normal flat tappet engine in regards to wear is idiotic. Whats next - 1.5L turbo Formula 1 motors from the 1980's to 1.5L Honda econobox engines for fuel economy? Just stop.
 
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Even stock hydraulic flat tappet cams with 90 lb springs and <.450" lift and turning <5500 rpm still operate in boundary lubrication. I don't see how a more viscous starting base oil is going to improve upon that when there is no appreciable oil film present. Say if we did have an impact of oil film, how can you substantiate any claims of better protection between different base oils of kinematic viscosity. This would claim that a 5w-30 using base oils with a higher pressure-viscosity coefficient wouldn't perform as well as a 10w-30 with a lower P-V coefficient. Are we just going to ignore the more relevant properties of these base oils and look at KV alone?
 
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Gokhan

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Originally Posted by RDY4WAR
Even stock hydraulic flat tappet cams with 90 lb springs and <.450" lift and turning <5500 rpm still operate in boundary lubrication. I don't see how a more viscous starting base oil is going to improve upon that when there is no appreciable oil film present.
Of course, any valvetrain always operates in the boundary-lubrication regime. However, boundary lubrication does not mean there is no oil film present. It means the oil film is thinner than the size of the asperities. Drain the oil and try running the valvetrain and see if it's going to last for a minute. Chevron shows the effect of the base-oil viscosity in a brochure: https://www.bobistheoilguy.com/foru...erature-full-shear-viscosity#Post5085549 In the boundary lubrication, the viscosity that matters is the base-oil viscosity because the VII goes under full temporary shear (polymer molecules fully aligned along the flow), as the shear rates are extreme, and the high-temperature, high-shear (HTHS) viscosity corresponds to a lower shear rate, applicable to the journal bearings instead.
 
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Originally Posted by Gokhan
Originally Posted by RDY4WAR
Even stock hydraulic flat tappet cams with 90 lb springs and <.450" lift and turning <5500 rpm still operate in boundary lubrication. I don't see how a more viscous starting base oil is going to improve upon that when there is no appreciable oil film present.
Of course, any valvetrain always operates in the boundary-lubrication regime. However, boundary lubrication does not mean there is no oil film present. It means the oil film is thinner than the size of the asperities. Drain the oil and try running the valvetrain and see if it's going to last for a minute. Chevron shows the effect of the base-oil viscosity in a brochure: https://www.bobistheoilguy.com/foru...erature-full-shear-viscosity#Post5085549 In the boundary lubrication, the viscosity that matters is the base-oil viscosity because the VII goes under full temporary shear (polymer molecules fully aligned along the flow), as the shear rates are extreme, and the high-temperature, high-shear (HTHS) viscosity corresponds to a lower shear rate, applicable to the journal bearings instead.
You're talking about the oil film present in boundary lubrication is greater than the polar molecules from the anti-wear and anti-friction additives? If that was the case, those additives wouldn't be necessary. Why would the pressure-viscosity coefficient of the base oil not be relevant here?
 

Gokhan

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Originally Posted by RDY4WAR
You're talking about the oil film present in boundary lubrication is greater than the polar molecules from the anti-wear and anti-friction additives? If that was the case, those additives wouldn't be necessary. Why would the pressure-viscosity coefficient of the base oil not be relevant here?
No, asperities means solid microscopic irregularities on the contact surfaces. [Linked Image from lh3.googleusercontent.com] Lecture notes on boundary lubrication -- University of Texas The pressure - viscosity coefficient (determined by the base-oil type) gives you the rise of the viscosity under high contact pressure (thousands of psi). We are still talking about the base-oil viscosity. Since the pressure - viscosity coefficient is something hard to measure (only difficult indirect measurements exist) and is rarely reported, it's of secondary importance to most people. There is no point of talking about something we have no data for. Moreover, the viscosity index (VI), which can be inversely proportional to the pressure - viscosity coefficient, also enters the equation and muddies the field even more when the temperature effects are considered. Besides, you hardly choose the oil by the base-oil type these days. For flat tappets 15W-40 is the best of both worlds because you get both a high base-oil viscosity and a high pressure - viscosity coefficient (the latter is because it has a Group II base oil).
 
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I know what asperities are. I've done a lot of cylinder honing, crankshaft polishing, and lifter bore honing. Even fine tuning a targeted asperity height, shape, and gap for specific applications. I was asking if you were saying the oil film in the gaps was more important than the polar molecules on the asperities. I can see where your argument is going, but it doesn't align with what I've seen with my own engines and others in the real world. Additive types and concentrations have made huge differences, but practically none observed with base oil changes. I feel like the activation of anti-wear additives in mixed and boundary lubrication is far more important than the base oil.
 
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Originally Posted by RDY4WAR
Even stock hydraulic flat tappet cams with 90 lb springs and <.450" lift and turning <5500 rpm still operate in boundary lubrication. I don't see how a more viscous starting base oil is going to improve upon that when there is no appreciable oil film present. Say if we did have an impact of oil film, how can you substantiate any claims of better protection between different base oils of kinematic viscosity. This would claim that a 5w-30 using base oils with a higher pressure-viscosity coefficient wouldn't perform as well as a 10w-30 with a lower P-V coefficient. Are we just going to ignore the more relevant properties of these base oils and look at KV alone?
I have 'upgraded' 75 POUND valve springs in my 22RE. I will trust my 15W-40 will provided all the film-strength and ZDDP necessary - for wear purposes....that's all I am really concerned with.
 
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