Flat Tappet Survival Depends on This: Camshaft Lobe Taper Measurement

Added: 2026-05-11

[00:00:05]Fly tapping cams continue to have a lot of confusing information about them.

[00:00:09]Today I'll show you one of the measurements that folks seem to not understand when it comes to what cam taper is and what it does to facilitate ro rotation. So we'll take a look at all those today and uh we'll actually measure a couple of cams. Let's go.

[00:00:23]We've done quite a few videos in this series where we talked about all sorts of things. Why we're having so many failures, what the problem is with engine oils and spring pressures and lifter to bore tolerance, which is one of the biggest ones that no one seems to be talking about and certainly no one is ever measuring at the machine shop prior to breaking in a cam, which is causing a lot of these catastrophic failures.

[00:00:48]Hopefully by now everyone knows that a flat tapet lifter must rotate to survive. And the reason why there is a crown on the lifter and a taper on the cam shaft lobe is to facilitate that rotation. But there are other things at play here as well too. One of the common things I see online is people saying, "Well, I bought this brand of cam and I bought a different brand of lifter." The problem with that is cam and lifter should be matched up based on the crown on the lifter and the taper on the lobe.

[00:01:22]If they are significantly off, you're going to have problems. The potential of that is extremely high.

[00:01:29]There are a lot of custom ground cams that are on the market today where the person that is selling them, the shop that is doing them for a specialty type of build will source a lifter from somewhere and depending on the crown on that lifter, they will have the cam ground. So, the lobe has the same type of taper. So, the two will work together. The problem is if you don't know those two critical pieces of information, you have no idea how those two are going to work together. I completely understand some people are so hyperfocused on brand and it's not really on brand. It's really about the quality of the machine work and what the lift to bore tolerance is and then all of the other things that you can do to protect that during breakin. its initial long-term break-in and its full service life of the cam. You've got to make sure that the lifter to board tolerance is good. If it's not if it's not that one and a half thousands of of tolerance between the two, you're going to run into some problems. And again, I see that over and over and over again in Facebook groups, Instagram, Tik Tok, whatever Facebook groups, it doesn't really matter. folks are are saying that they've tried to do a breakin on a cam and it wiped out and they go, "Well, it must be brand X or Y or Z and it's just junk. It's all China." They have no clue what it is. Whereas the problem really boils down to they have no idea what that lifter to bore tolerance is. They didn't use a formulated break-in oil.

[00:03:09]They ran spring pressures that were way too high. We're not talking about engine blocks here that are 10 years old anymore. All of that was completely relevant back in the 80s and 90s when engines didn't have near as much miles on them. It was very common for us to go into a machine shop and say, "Hey, can you tell me if that is uh the what piston I can run in there? Is it too worn?" And when it's the cylinder is worn, what do you do? You bore it and you put an oversized piston in it. What do you do when the lifter bore is worn?

[00:03:43]No one knows because your machinist isn't telling you that information.

[00:03:47]We've talked about that over and over and over again. And I hope that at some point that sinks in or someone sees that prior to doing a build and a breakin and asks a machinist that right question so they can correct those tolerances to make sure that you get it right and help yourself give you a good initial breakin on that engine and get a good long service life out of that cam. So I'd highly suggest you go look at some of the past videos in this flat tap it cam series that I did and take a look at that. We measured five or six, maybe more different lifters to measure the crown on it to see what they are. Again, if you're running a crow cam, run a crow lifter to go with it because again, the two are matched together. So, as that lifter rides on that lobe, you're going to get the rotation that Crower designed to put in there. Now, Crower Comp, uh, I can't remember some of the others, but those are the two primary ones use that taper that the OE used. Why? Well, the OE's had it right, especially General Motors, Ford, especially GM with all of the single engine platform they spit out in small block and big block Chevrolets.

[00:05:04]They made millions of those damn things.

[00:05:06]they figured out what the correct tolerance was between the lifter and lobe to facilitate good rotation. So, go check out those other videos. I think you're going to learn a lot. And the last thing that we have to measure so now that we're done with doing the crown on the lifter is let's take a look at the taper on the cam shaft. I see that comment quite a bit that the problem with today's cam shafts is there is no taper ground into it. I disagree. There is plenty of taper in it. It's just that are you matching them up correctly with the lifter and all of those other little details that you need to consider when building that engine. Okay, let's talk about taper and how it's measured here.

[00:05:49]I'm going to draw the top side. Let's look at this as a cam lobe. And hopefully I'm going to overexaggerate this a little bit, but there is a taper in the lobe to again to ensure that as the lifter rides on there that it fatil facilitates that rotation of the lifter.

[00:06:09]When measuring taper in a cam, you're only measuring about 300,000 worth of of distance here. So that distance between those two points you don't measure tip to tip or edge to edge you are just measuring that now taper all as that is is the difference in the angle from one starting point to another. What is the difference in inches of that taper from that starting point to the end point. So that's what we're going to do today.

[00:06:40]I've got three different cam shafts to look at here. I have a comp, I have a Illuminati, and I have a crane cam that we can look at all three of them and measure them and see where they're at. I also have a couple uh cams that have uh destroyed lobes on it. We'll take a look at that and see what that looks like in that difference. But let me go ahead and get the the stand set up. We'll talk about how we're going to measure it. We have to first make sure that our workspace is level. So 0 0 0 0 0.

[00:07:22]We are good on all four corners. So, we are nice and level. Ready to start. When we measure these, we don't want to measure it over the nose. We want to measure it on the base circle of the cam. So, I'm going to do that. I'm going to take this cam and I'm going to measure out that 300,000 of uh space there. So we can take a look at that way when I'm going to measure with the pointer, we get it in the exact spot. It doesn't have to be completely accurate because honestly what we need to do here is we need to take an average of multiple different loes to make sure that we're within whatever tolerance it is. Now that we got that set up, gauges zeroed out, all we're going to do is we're just going to slide the the mic over, the dial indicator over so it can get a good reading between that distance. Remember, we're not going edge to edge. We're going inside the edge, but 300,000 on the inside of that. So, right now, we're at zero. If we slide this over, you will see we ended up right on our mark at exactly where that tolerance should be. Remember, this is a comp cam.

[00:08:32]Comp is similar to crow. Uh, again, I can't remember the others, but Comp and Crower follow that pretty aggressively where they are on that OEGM spec. I don't know what the cam shaft was for, but most of the cams are ground that way because all of their lifters are that way. And that is where we're at, 1 and a half thousand between those two tick marks. That comp cam is within tolerance on the taper. Now, again, you need to measure a bunch of these loes. That's why those really cool uh ad call reports that Comp Cam has where you can send in a cam shaft. Not sure if they still do that anymore. I know they do that on their own cam shafts where every single cam that goes through their cam shop gets measured on an Adole machine. That machine will measure seven digits below the decimal point. very very precise piece of equipment because that's what they want to know when they are measuring lift and duration and taper and all of the critical dimensions on a cam shaft. So now that we know that this comp is where it's supposed to be, it has the correct taper in it for the lifters that they sell, let's take a look at the um theat one next and we'll measure it. Okay, same measurement here.

[00:09:52]Just going that 300,000 distance. So, let's slide over.

[00:10:02]And there we are. We are at the same now. I knew that that was going to be the result because every cam that comp grinds, whether it's comp, whether it was the discontinued valveetrain, whether it was a discontinued crane brand, blue racer, all all of those cam dynamics, all of those brands that comp owned, they ground on the exact same taper on most of their flat tap it cams depending on the lifter that's going with it. Now, obviously that wasn't the case all the time, but that's pretty universal for the COP stuff. They are really tight on that tolerance. Again, um those ADC cold machines, there's three of them in there um that they use to test all of those cams that come through there. It's deadly accurate. So, doesn't surprise me. And again, because these all came from comp, the facility that grinds it, they all should be on the exact same. So, now that we've got that one done, I'm going to go ahead and I'm going to fast forward. Let's look at one that's got it some destroyed loes on it, and we'll see what the taper looks like on a cam shaft that's well, a little jacked up. I have no idea what this one's going to be. Uh, but it has been run before. So, um, we know that there's potentially this one has X's on there. I don't know if I put those on there or if somebody else did, but the Parkering has worn off on this cam. It's definitely been run. So, let's take a look at pointtooint and see what that difference is.

[00:11:43]Okay, we can see again, I don't know anything about this cam. Don't have any notes on it. So, no big deal. But again, measuring straight across at the base circle of the cam, we are still at the tolerance. So, whatever that is, however worn that was, which doesn't look like it was terribly worn, but something happened to this thing. And uh well, obviously it was dropped. Cast cam cores don't handle that type of uh abuse very well. That grey steel stuff will snap.

[00:12:12]Whereas a billet 5150, 5160, 8620, those are common materials. They don't really break like that. But cast cam cores, yeah, we got to be careful with your UPS guy, your FedEx guy. Make sure when you get your cam, uh, you inspect it right away. But whatever that wear was, it wasn't enough to change the tolerance on the taper on that cam shaft. Would I have liked to have gotten several other brands of cam shaft to look what the taper is? Yeah, I would. But uh to be very honest with you, I'm not spending a,000 bucks on flat tapic cams to buy a cheap Summit brand, a crow, uh maybe a Elgen or something else on the marketplace just so we can measure taper on it. Uh, but very very specifically, I would ask that cam manufacturer that you're going to go with of what the crown is on their lifters, what the taper is on their lobes, and then your machinist should be able to verify those things for you, that the lifter and the taper on the lobe match up correctly.

[00:13:18]Again, be very careful doing that. I've seen that failure multiple times where again somebody thinks that one brand of lifter is better than the other and they're mix and matching brands and what you're really doing is you are potentially mix and matching the crown on the lifter and the taper on the lobe and that's a recipe for bad ju guu. I hope that answered some of your questions. Again, I see that over and over again where people will just make comments that, you know, today's cam shafts don't have any crown on the lifter. There's no taper on the on the cam loes. Look, the recipe hasn't changed. If you have a cam manufacturer, comp, Elgen, again, Crane, Lunati are gone, Howards, any of those big good name brands that are out there, they've had that same recipe forever. It's not that the master on an old Burkco, you know, cam grinder or whatever they're grinding these on has changed. It's all the same. So, it's not like the recipe changed. The cam cores are all generally gotten from.

[00:14:26]Again, if you follow a good name brand, they're mostly made in Michigan. I think there's maybe one or two places still left in Ohio, but for the most part, Michigan's the place. And unfortunately, uh, one of those suppliers I know, I believe is not going to be making, uh, cast cam cores anymore. Why would they?

[00:14:49]Um, with blocks wearing out, failure rate getting too high for them, it doesn't make any sense. The OES are all using roller. So, when you switch from going to grinding a 5150 material, for example, to a gray steel cast cam core, it changes the machine. It changes what you're working on, setup time, all that stuff. It's much easier on an actual CNC machine on a good Landis that can crank out quite a few cams every hour. Just doesn't make sense. So, I understand why they're going away. But unfortunately, because of that, you're going to see a lot of stuff that's coming from offshore. But again, if you stick to the name brands, they're not buying their camcords from offshore. They're not buying most of their lifters. I can't say all of them, but they can't they're not buying most of their lifters from they're getting them from High Liift.

[00:15:43]They're getting them from Delo is still making a few of or uh Deli is still making a few of them. Uh but uh yeah, there's a again it's a diminishing market. So I understand you want some folks want really inexpensive, cheap and all that, but why go through all this? Just go put a hydraulic roller in it. Have fun. Get some good long durability on it. Don't worry about anything. Have a good breakin, good long service life. If you still want to run flat tapet stuff, you can do it. You just got to be really careful about it. Leave your comments down below any of these videos in the flat tapet series. Please share those when you see people having questions about it. It will help them figure out what's going on. Ask the right questions of their machinist. Ask the right questions from their cam supplier. Make sure that they're getting everything matched up. make sure that they've got, you know, the right spring pressures on breakin. Make sure that their to lifter to bore tolerance has been measured by their machinist every single hole and verified. All of those things are brutally important. Um, and the older these blocks get, the more worn they get, and the fewer machinists that are out bushing them or using an oversized lifter in any of those is pretty uncommon, unfortunately. So, um, unfortunately, machinists are not like they used to be where, you know, here in Memphis there was probably 15 or 20 good machine shops. There's probably one if you're lucky. And I don't even know if I would trust that one. So, anyway, leave your comments down below. Happy to answer them for you. Please watch the rest of the videos in the series. Give me a thumbs up if you watched it. Um, leave a comment. Helps me out on the channel quite a bit. Um, it's the old like, comment, subscribe YouTuber line, but it does help quite a bit. So, anyway, we'll catch you guys on the next one. Hope you learned something out of this one. And if you got to break in on a flat tap of cam, do your research. You can get it right. You just got to know what you're working with. We'll catch you on the next one. We'll see you.