I’m hearing all kinds of conflicting information about guys losing flat tappet camshafts in engines thousands of miles after the engine was built. It appears the favorite bad guy is the camshaft companies using poor quality metal cores, made with subpar metallurgy and bad heat treating processes. I’ve read so much about this on social media I’m wondering what your take is on this?

T.M.

Hot rodders are just like other people in terms of commenting on a subject and offering their opinions and favorite “solution.” It is human nature to look for an uncomplicated answer or a clearly-defined “bad guy” they can call out to quickly explain a very complex topic. So let’s see if we can point to some facts instead of rumors, opinion, innuendo, and scare tactics.

First of all, I have a very good friend Billy Godbold who, until recently, was the cam designer and head of Valvetrain Development and Engineering at Comp. I get many of my facts from him. Right out of the gate, he has told me on several occasions that he has never seen a flat tappet camshaft fail because of bad metallurgy or poor heat treatment.

I’ve also heard that a few cam companies have stopped selling flat tappet camshafts because of all the problems associated with improper flat tappet break-in and maintenance of the camshafts. It’s not because the cam company can’t make a good product. It’s more because they can’t control how the cam is used after the cam comes out of the box. So they choose to stop offering these cams because of all the unhappy customers who did not want to hear that user/installer errors are the cause of a majority of the problems!

Oil, Break-In & Flat Tappet Cam Design

Right away the finger pointers will say something like—why didn’t we have these problems 30 years ago?

The answer is because oil has changed dramatically in the last few decades. Everyone should know (but many do not) that zinc and phosphorous (ZDDP) levels have been significantly reduced in API oil that you buy off the shelf. This oil should never be used with flat tappet engines using anything that approaches a performance valve spring. You can’t even run diesel oil now as that oil is not the same as it was even five years ago. The new diesel engine oil today essentially offers the same low ZDDP levels of current SM/SN gasoline engine oil.

We’ll hit a couple of topics that no one talks about mainly because most self-proclaimed “experts” are not even aware of these situations. First of all, flat tappet lifters are not really flat. They all should be machined with a slight crown near the center of the lifter. This crown helps the lifter to rotate in the lifter bore, which it must do in order to survive the contact with the cam lobe. Next, there is a slight taper ground into the lobe that also induces a spin in the lifter.

From talking with cam designers and grinders, it’s important that the lifter crown be closely matched to the cam lobe taper. So when you have “builders” mixing and matching lifters and camshafts, it’s a crapshoot as to whether there is a proper relationship to produce each of the 16 lifters to spin. If even only one lifter fails to spin—that lobe will fail. End of story.

I recently read a post where the author claimed he had lost three camshafts and all three failed the same lobe. Of course, he blamed the cam company. But from that one fact, it would appear that specific lifter bore did not allow the lifter to spin. It should also be clear that this failure had nothing to do with the cam itself. It would appear that he had a bad lifter bore that did not allow the lifter to spin.

We will skip over the concept of a proper break-in procedure because that topic has been well covered in the media and in this column. But we will emphasize that a high quality break-in oil with roughly a 1,500 parts-per-million (ppm) concentration of ZDDP is essential to achieve proper break-in.

Read more about proper flat tappet cam break-in here:

I have used flat tappet cams in dozens of small block Chevys with only one failure over the last 20 years, and that was due to using a poor break-in oil that did not have the proper zinc and phosphorous levels. I know that because we had the oil tested to measure the ZDDP concentration—it measured close to 800 ppm, which we considered insufficient.

The last flat tappet engine I built was in 2022, and it easily survived the break-in process. I consider the claims of poor metallurgy as unfounded. The “experts” who claim otherwise are using opinions and ignoring facts.

Camshaft Health After Initial Break-In

But there’s more to this—much more.

Even after the flat tappet camshaft has successfully broken in, that’s not the end of the process. This sliding friction liter/cam interface must use a high zinc performance oil to maintain proper lubrication. End users must not use current SM/SN API oil because the ZDDP levels in these API oils are too low to ensure minimal wear.

As an example, let’s say we have a performance camshaft in our small block Chevy and broke the cam in successfully using a high-zinc break-in oil. But now with 500 miles on the engine you change the oil and use an off-the-shelf API SM/SN oil because it’s convenient and less expensive. The camshaft will likely live for many miles with this lower ZDDP oil—but the reality is that the cam and lifters are slowly deteriorating and this accelerated wear will eventually show up as a flattened lobe or concave lifter.

That’s when the uninformed are quick to rush to judgment that the metallurgy was to blame

The reality is that, the end user did not protect his investment by using a quality, performance oil that includes a sufficient ZDDP levels of around 1,400 to 1,500 parts per million of ZDDP. This, along with proper additive packages in the oil, will protect the lifters and cam and allow the valvetrain to live for a very long time.

It’s also possible that lifter alignment to the camshaft is another potential source of problems. Poor lifter bore wear can create issues where the lifter will not rotate due to excessive lifter bore clearance. This can cause accelerated wear as the lifter lightly cocks in its bore. It’s rare to find an engine builder who actually measures the lifter bore clearance on an engine block that might be 60 years old and already experienced 200,000 miles of use. If you think those lifter bores might be worn compared to a brand new block, the answer should be obvious.

Also, did you know that high detergent levels in engine oil works to strip ZDDP from the working surface it’s trying to protect? That’s a fact. That’s why diesel oil isn’t a good choice because diesel oil has very high levels of detergents compared to gasoline engine oil.

How to Keep a Flat Tappet Camshaft Happy

So to answer your question, it’s imperative that a flat tappet camshaft be lubricated with the proper performance engine oil that contains higher levels of ZDDP—usually around 1,400 to 1,500 parts per million (ppm) so that the cam has a chance to survive. But beside that, you must break the cam in using low spring pressures.

If the spring seat load is greater than 100 to 110 pounds, it’s likely is too much spring pressure for break-in. Don’t assume that the spring that the cam company recommends is also the spring you would use for break-in. These are two completely different concerns. Use a near-stock spring for break-in and then install the proper spring once the cam has established its wear-in pattern.

Another good idea would be to do an occasional used oil analysis to see if there are excessive wear metals like iron in the oil. If so, this could be a warning that there is a problem that should be addressed before something fails. The best procedure is to do a yearly or bi-annual oil test to get an idea of the condition of the engine. This is a hassle and not without some expense, but the alternative is an expensive engine repair that might have been averted.

The bottom line is that you need to use specialty engine oil for any performance flat tappet camshaft engine. Stock engines, like a mid-1980s to late 1990s small block truck engine can probably survive using a normal API SM/SN off-the-shelf oil because the spring loads are very low which will not destroy the cam. But there is no guarantee on that. You are likely taking unnecessary chances with an engine with a flat tappet performance cam using current off-the-shelf SM/SN oil.

The best idea is to always use a performance, high-zinc oil.

Best Performance Oil for Flat Tappet Engines

A bottle of Summit ZDDP enhanced motor oil
The best way to protect a flat tappet cam once it is broken in properly is to use a high-ZDDP oil. There are several to choose from which include Summit’s performance oil like this SAE 10w30. (Image/Summit Racing)
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Ask Away, flat tappet camshaft, Jeff Smith
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.