A cam follower and a micrometer (tale of the tape)

So I've been following the threads about worn cam followers, and was persuaded to change mine out at 32,000 miles. Some have argued that it really is unnecessary to change it, and that the followers that have failed were just a batch of bad followers that got into our engines.

I had a micrometer laying around, so I measured the wear of my old follower versus a new one. (Both measurements were made in the center of the CF).

I'm hoping some actual measurements will help solve this problem, and give more info than looking at pictures of wear on the CF.

1.Left - new CF
Right - Old follower (32K and almost four years old - and I make a lot of short trips in cold weather). DLC is gone, but very even wear.


2.Old follower -777 microns (conservative - I'd guess it's really close to 777.5)


3. New CF -781 microns


Total wear over 32K miles is a grand total of 4 microns. That rate of wear should give you well over half a million miles before you've lost more than 10% of the total thickness of the CF. (4microns of wear/ 32K miles. 10% of 781 = 78. 78microns/4microns x 32Kmiles = 624K miles for 10% cam follower wear.)

While the loss of the DLC may increase the rate of wear, I don't think it is going to increase the loss of wear so fast that the CF will fail under 100k miles. Plus, these engines are bench-tested for thousands of hours, representing hundreds of thousands of miles, and a design flaw as significant as is being reported should be easily evident.

I think a supplier screwed up and delivered some soft metal - and some of us are paying the price, and the rest of us don't know who will be next.

I'll check my new cam follower at 60K miles, and if the wear is similar to what I've reported, I'll just keep that CF in there.

Hope this info helps some folks out.

Wow thanks for all your hard work! Wish there were more guys like you! I haven't checked mine yet but I plan to change it anyway... I have an 07 with a stage 1 apr tune

I don't think your wear estimate will hold up. The DLC wears much slower than the bare metal, so once the DLC is damaged or gone, wear will accelerate greatly. The fact that people wear through their cam followers in far fewer than half a million miles corroborates this.

Does anyone notice any change in performance, knocking or fuel mileage before they change the CF? I was talking to my service tech and they said if I had a reason to believe that there was something wrong and they discovered that the CF was the problem then this would be covered under warranty.

you would get a cel and possible fuel cuts

Wow great work man, I just wish ur calculating would be the actual life of a cam follower.

I doubt your measurements are accurate to 4 microns.

and there's obviously more than 4 microns of wear.

someone whose cam follower failed would laugh if you showed them the 600k mile calculation

i agree about the wear probably accelerating after the dlc is worn off, but it's great that you were able to get that info!

From what I have seen over the years on the forums, cam followers typically die once the contact surface prevents the follower from spinning as it was designed to. You may have only lost 1% of the follower thickness at that time, but once the follower stops spinning, you will lose the other 99% relatively rapidly.

Interesting results nonetheless. Which cam do you have? A or B?

Wtf is this micron crap?

old one is ~.0775" & the new one is about .0811"

That a difference of about .0036" (for those of you keeping track at home, a piece of paper is about .004")

Paint is only a couple of thousands thick at the most, so I'd say you were starting to wear through the follower itself. I thiink thats when people start getting in trouble

Wtf is this micron crap?

old one is ~.0775" & the new one is about .0811"

That a difference of about .0036" (for those of you keeping track at home, a piece of paper is about .004")

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1000 microns = 1 millimeter. You're using inch symbols in your post; this is metric units of measure. But you're right -I can just barely slip a piece of paper through the micrometer set at 4.

From what I have seen over the years on the forums, cam followers typically die once the contact surface prevents the follower from spinning as it was designed to. You may have only lost 1% of the follower thickness at that time, but once the follower stops spinning, you will lose the other 99% relatively rapidly.

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This makes a lot of sense. A lot of sense.

Interesting results nonetheless. Which cam do you have? A or B?

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Cam B - the good, two-piece unit.

I doubt your measurements are accurate to 4 microns.

and there's obviously more than 4 microns of wear.

someone whose cam follower failed would laugh if you showed them the 600k mile calculation

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The micrometer I used is $105 new - it's pretty accurate. I measured both CF's a few times to validate the precision of the measurements, and then posted pictures of what I believe are very accurate measurements. Then again, I'm not an engineer.

I don't think your wear estimate will hold up. The DLC wears much slower than the bare metal, so once the DLC is damaged or gone, wear will accelerate greatly. The fact that people wear through their cam followers in far fewer than half a million miles corroborates this.

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I don't think half a million miles is a great estimate either - lots of other factors come into play, as I'm sure the metal softens with repeated heat cycling, exposure to more metallic shavings in the oil as the engine ages, etc.

I just don't think that VW designed a part that can't last more than 50K miles. Wear of a CF from a spinning lobe is pretty basic (I would think) for a materials engineer. I'm just theorizing that a supplier screwed up or, as above, there is something that causes the cam follower to stop spinning. This guy's CF may be showing evidence of that.

Wow, either way the working surface of our followers is only 1/32 of an inch think? I would have guessed it was thicker. Are you sure it's reading right?

so, you think those rings of wear around the center are 4 micron? I doubt it, can you think of any other metric for cam follower wear? I doubt the wear rate is linear for the cam follower.

You're making an assumption that the cam followers are produced to a precision that is unlikely. Unless you start with 2 new followers and measure both to know how they compare before any wear your comparison is not valid. Confirm that they were identical down to the micron from the get-go and you've got something.

Joy Division said:

Wow, either way the working surface of our followers is only 1/32 of an inch think? I would have guessed it was thicker. Are you sure it's reading right?

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Ever check out how thin the aluminum fuselage of a modern airliner is? It's just a little thicker than this (presumably hardened) steel CF!

The gauge is accurate.