Just what exactly is a "flat-tappet cam" re:zinc

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I had no idea that SM oils had reduced zinc or did i know that zinc was an anit-wear ingredient in oil, until I started reading this board. So naturally, yet something new to worry about (or not). So, putting aside the issue of zinc and its role in engine wear and not to debate it (in this thread anyway), do I have flat tappet cam motors in the following? 1993 Nissan Sentra 1.6 DOHC 2005 Nissan Fronter 4.0 DOHC
 
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Do not worry about it. Cam and tappet wear is tested with a Nissan 2.4L engine before a oil is certified for SM/GF-4 and soon SN/GF-5. The only people that may worry about it are people with high performance engines with high pressure valve springs to keep valves closed at high RPM.
 
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No. And if you think about it, even the API (and ILSAC) in their infinite wisdom would not release an oil specification that would destroy such mundane engines. And it's not Zn, it's P. Just so you know, not to rehash the discussion.
 
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 Originally Posted By: Pablo
No. And if you think about it, even the API (and ILSAC) in their infinite wisdom would not release an oil specification that would destroy such mundane engines. And it's not Zn, it's P. Just so you know, not to rehash the discussion.
+1 Pabs just said it all.
 
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Here's a picture of a flat tappet cam. The cam is covered in gray grease. The lifter is just a cylinder of steel coming down vertically and riding on the cam. So instead of a ball bearing rolling along the surface of the cam, you have a chunk of metal scraping across it. This is very prone to wear, obviously. And here is a rollerized OHC setup, like you probably have on your cars. You can see a small ball bearing rolls along the cam lobes, which increased price and complexity but reduces wear and friction: Not all OHC engines have roller bearings between the cams and the valves, but it's becoming the norm.
 
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So then would this mean that my BMW M52 engine is technically "flat tappet"? Unfortunately this is the only picture of my set that was out of focus, but it's also the only one that the lighting shows the HLAs. Exhaust cam only is uncovered: If this is the case, and I believe it is, I think that some people are going to have to retreat from the position that flat tappet protection is only for yard equipment and ancient muscle cars. At the same time, more than a decade of BMW owners aren't freaking out about sticking with API SL and pouring bottles of zinc additives into their oil. My UOAs show no wear factors. I certainly don't see any rollers, but it also isn't a "low performance", "low technology" or "old" engine.
 
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Are they solid? And I tell you guys, metallurgy is key as well. Just because an engine has some form of flat tappet, it is not prone to wear more with SM oils.
 
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Yeah, those are bucket lifters. The lifter sits on top of the valve and spring assembly.. Im with Pabs. I find it very strange that a certain few companies making aftermarket cams have a problem with oils. Could it be a manufacturing shortcoming? Until someone delivers a melted cam to a metallurgist, the world will never know. But also note that I said, "high performance engines with high pressure valve springs to keep valves closed at high RPM." Upgrading the springs when upgrading the cam is common and often recommended, since performance cams will have higher lift rates than stock and or higher total lift than stock. Because these features will literally throw the lifter off the tip of the lobe if the spring is too weak, it is easy to see why. But the result is much higher pressures on the lobe.
 
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I still say in high performance older V-8 applications with a flat tappet cam, there is still a problem with lack of zinc in SM/GF-4 oils, EVEN with good quality camshafts. It's well known. Now, in a passenger car engine with a DOHC bucket/lifter/shim type flat tappet arrangement such as the BMW posted above, or what Toyota and many Japanese manufacturers use, it's not an issue since valve spring pressures are probably a quarter what they are in a high lift solid lifter OHV V-8.
 
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Yeah, that is another thing I didnt think of. In a OHV you have to control the Valve, Rocker, Push rod, lifter, and the weight and inertia present with all these components.
 
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 Originally Posted By: ekpolk
Click here to see a nice article that pretty well sets out the basic difference between flat and roller designs.
Excellent article! That`d how I always thought a flat tappet cam looked. Seems way more primitive than a roller cam. Are all modern engines roller cam nowadays? Seems like a much better design wear-wise.
 
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My Honda is rollerized, my Toyota is bucket over (non rollerized DOHC). On the new Toyota 2arfe, which replaced the 2azfe in the Highlaner, Rav4, Camry... one of the improvements was to rollerize the valvetrain. With the same transmission it gets 1mpg better FE on the Rav4, and gives more power. I wouldn't say the valvetrain is the major reason for the improvement, but I'm sure the change was done to help with that, not to reduce wear which wasn't an issue. Even though in the bucket over there is metal sliding on the cam, I never see much wear on cams and I agree this is due to much, much lower moving mass and the resulting lighter spring pressure.
 
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The 4.0 Jeep engine is currently and has been having camshaft issues for the past few years, there are a number of reported failures talked about on the Rubicon Owners Forum, and on a few other web sites devoted to Jeeps. I primarily work with John Deere, but from time to time have worked at Jeep dealerships, most recently 2006- 2007. We had a number of newer production Wranglers ending up with new camshafts. I refuse to use SM rated oil in my 2006 Rubicon except that the new Delo LE is SM rated, and I will use it. I have noticed the Mobil 1 HM is SL rated and I am seriously considering switching to it. There is a notion that you can use just about any oil in the 4.0 and you will be fine however for the duration of my time at the last Jeep dealership the mechanic who did heavy engine work was consistently replacing a cam every week or two, the Jeeeps ranged in age from about 2002 to 2006.
 
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 Originally Posted By: Pablo
Are they solid? And I tell you guys, metallurgy is key as well. Just because an engine has some form of flat tappet, it is not prone to wear more with SM oils.
But it is not immune to excessive wear with SM oils either. I've been over this for years on the TurboRegal boards. It's probably the biggest collection of high performance engines still using flat tappets anywhere and there's tons of good info. Stock engines with stock cams and springs do go bad from SM oils. It's fairly rare but it does happen. Add a mild aftermarket cam and slightly stiffer springs and it's a necessity. I wouldn't worry as much with the OHC engines because they usually run a wider lobe and lifter and less spring pressure.
 
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 Originally Posted By: Pablo
No worries with that bucket set-up.
Hydraulic lifters with "buckets" are obviously common in many engines. All my VW and and Audi engines had that setup. Just to make sure about the used terminology: hydraulic lifters still do qualify as flat tappets, with the "bucket" representing the flat tappet, correct? As far as I know, running in a flat tappet cam, usually a rebuild, with a low SAPS oil may be less than ideal.
 
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one thing to consider: on my volvo 850 it has those flat lifters but they are free to rotate in the well and equalize the wear. some domestic setups i've seen lock the lifters into place which would force them to wear in one way.
 
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