What the Cam??? Learning About the Camshaft

While most of the general public would be able to recognize a “cam” as a part of an engine, and possibly many could even point out the part if seen lying in a junkyard (or am I giving the general public too much credit?) – but if you took a poll of random people on the street, very few could tell you what a cam actually does. So what does a cam do?

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Put simply, a cam, a.k.a. camshaft , is composed of lobes which dictate when and for how long your engine’s valves stay open for. The opening and closing of your valves has everything to do with how your engine runs, how much power it has, and it’s fuel economy. In order to understand more, you’ll need to understand the basics of how an internal combustion engine works…. the cam affects the whole combustion part of your combustion engine.

Where a cam goes in your engine depends on your engine. In older engines, like the Small Block Chevy (SBC) in my Studebaker, cams are generally found in the lower part of an engine above the crank and connect to the valves via pushrods and rocker arms. The terms SOHC and DOHC denote more modern designs where the cams are at the top, either a Single OverHead Cam (SOHC) or a Dual OverHead Cam (DOHC). In these designs, pushrods are unecessary as the cam(s) comes in direct contact with the valves.

While defining what a “cam” is sounds pretty simple, the truth is it touches on something very few car hobbyists truly understand- and that’s how all of the pieces of an engine work together. It’s like someone saying they understand the human body because they can sing the song “the hip bone’s connected to the thigh bone…”. Sure, they may know the basics, but it doesn’t mean they’ve got full understanding of how a body works. A molecular biologist could not only tell you the bones, but also all the cartilage, muscles, tendons, and molecular structure of how that affects movement. And while a car isn’t quite as complex as the human body, you get my point; just because you know how a cam works and can change a cam out in an engine doesn’t mean you fully understand its role.

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I recently had my own rude awakening of my still-growing mechanical knowledge when I rebuilt Studie’s engine. The engine originally in Stude was built by a stranger… built for the drag strip. Little by little I’ve uncovered my engine’s mysteries, and decided during the rebuild I needed to add back in some more milder drivability. I decided to swap out my intake manifold and carburetor for more moderate performance parts, things more suited for street driving. Against suggestions, I decided to keep the cam; reasoning, “I still want my engine a bit aggressive.”  What I wasn’t taking into account, is how all these different parts of the engine work together. Although I’ve never had the specs on my cam, based on the ever-present lope of my engine and the other parts originally used, I’d assume it’s a very performance-oriented camshaft with a lot of cam lobe overlap.

Now post-rebuild I’m finding out that tuning my car is near impossible, because I have nearly zero vacuum at idle. This all has to do with the cam and how it doesn’t keep my cylinders shut long enough to build up pressure… which is getting into more complex explanations of a cam’s job! I’ve learned the hard way that having just one aggressive performance part in your car will actually make it run like poop…  the whole thing will be out of sync. It would be like someone from your local flag football league trying to go and join in on a Superbowl quarter; they’d throw the whole team out of whack and it would be a disaster!

So, before you budding gearheads out there run out and start swapping engine internals for performance ones take some time and get to know your engine even better. Get a good understanding of the bottom line and all of the basics coming into play before you start throwing parts at something and be sure to wrap your head around the more brainy part of mechanics (my Engine Building Basics article is a good place to start) rather than just doing what you saw in a magazine or the latest person at a car show told you. As for me, I get another opportunity to dive into Studie – I’ll be swapping out her cam and getting something milder. Now on to chat with some folks much smarter than I about what cam I should choose, do my research, and make a well informed decision!

Happy Trails,
Kristin

Continue reading about my cam adventure in the next article, Choosing a Cam: Passing the Learning Curve!

3 Responses

  1. JP Kalishek

    while folks always consider DOHC and SOHC “more modern” designs, many very old cars had these features, some not so exotic. iirc the first were Grand Prix cars of the 1903 or so era, but then production cars started coming with them. What really drove the Europeans I think was the many laws aimed at Ford’s Model T. Many places had a tax on engines over a certain size (and that size always seemed to be just under the Ford T engine size of 2.9 liters) so to get the more powerful engines for their lower price point cars they needed to find other ways rather than just make the thing bigger. Even after things changed or folks pretty much ignored the tax adding cost they were still expecting certain things from their engines, technology-wise, and for the most part engines stayed near that 3 liter size.

    Here in the US we had a few of them (Crosley’s brazed engine, Jeep’s Tornado, Pontiac’s 230 Six) but tended to stick with the old stuff, and what we mostly got in OHC stuff was imported (Pinto stuff from Germany, Opal as well, Dodge got Mitsu stuff … my favorites btw are those 1.6, 2.0/2.6 chain driven cam motors Ford/Mazda and of course Toyota, Datsun/Nissan, and Honda etc.) or versions of an import redesigned here.

    I often wonder how much the Pushrod designs were because some early flatheads were converted to OHV by using a bolt on head with pushrods in place of the stock valves, one thing leading to another.

    Reply
  2. Russ Bellinis

    One thing not mentioned in either of the articles that I read on camshafts here was the question of whether you have flat tappet lifters or roller lifters. Until the 1980′s, virtually all production V8s in the U.S. used flat tappet camshafts. Roller lifters were strictly aftermarket. The advantage of the roller lifters is that you can have a much more radical camshaft and still have a decent idle and good low end power.

    There is a problem however that has cropped up with engine builders in recent years. Because the roller lifter reduces friction between the cam and the lifter, roller cams are not case hardened. Camshafts designed for flat tappets must be case hardened, or else the camshaft lobes will wear out in a matter of minutes after the engine is started!

    A friend of mine who has built a lot of engines has found a lot of engines supposedly rebuilt by professional engine re builders where the “mechanic” has installed flat tappets on roller cams, and then the guys have the car towed to my friend’s shop to find out why the “new” engine won’t run! When he pulls the valve covers, the lobes are worn round, and the valves only wiggle instead of opening and closing!

    Reply
    • Kristin Cline

      Flat tappets on roller cams!? Just goes to show you that there are plenty of blockheads out there! But hopefully… they live and learn just like me!
      My cam is a roller along with roller rockers ;) Which reminds me, I have lots of writing to do to catch up here on Grease Girl!

      Reply

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