Andrews Explains the Camshaft
Everything You Wanted to Know But Were Afraid to Ask
Many riders out there know what a cam is, but most don’t quite understand exactly how it operates. We had a few questions that we wanted answered. As usual, when we ask a question, we want the correct answer from experts, so we contacted Andrews Products.
John Andrews started Andrews Products in early 1972 and started selling cams in 1974. Since then, the company has come a long way and now uses state-of-the-art engineering design and manufacturing technology for producing superior quality camshafts, along with a series of other components. We had a long conversation with John about camshafts, and here’s how he answered our questions.
HB: What is the general function of a cam?
JA: The basic function of a cam as applied to engines is to convert the rotation of the crankshaft into lifting motion that opens the intake and exhaust valves in the heads.
HB: What is the difference between an Evo-style cam and a Twin Cam design?
JA: The difference between an EV80 cam and TC-88 cam is that the EV80 uses one four-lobe cam, and the TC-88 uses two separate camshafts, one for the front cylinder and one for the rear, with two lobes on each cam.
HB: Is there an advantage to a Sportster’s four-cam setup?
JA: The only advantage to a four-cam arrangement, as on Sportsters, is that the engine case assembly can be considerably narrower. A four-cam arrangement also has the distinct disadvantage of much more expensive manufacturing costs and more possible noise with six different precision gears running together (four cam gears and two drive gears).
HB: Define lift as it relates to a camshaft.
JA: The term lift refers to the total movement of a valve in a seated position to wide open.
HB: Define duration as it relates to a camshaft.
JA: Duration is the term given to the event length in crankshaft degree between a specified height. If someone says they have a cam with 260 degrees of duration at a lift of 0.050, it means that the lifter for that cam lobe is above a lift of 0.050 for 260 crankshaft degrees of engine rotation.
HB: Define cam timing.
JA: Cam timing refers to the crankshaft positions in degrees where the intake and exhaust valves open and close.
HB: In regards to a Twin Cam, what is a base circle, and what does the term base circling mean?
JA: The term base circle means the lowest lift point on a cam lobe. Typically, this will be true circle for about 100-or-so degrees of cam rotation. We think a cam should be manufactured the way you want it the first time, so no modifications are made to the cam, but the term base circling means reducing the lowest lift point on the cam lobe to accommodate higher lift. If this modification is made, other components must be changed as well to compensate for the new shape of the cam, which can be expensive and time consuming.
HB: What are the advantages of a Twin Cam geardrive?
JA: The advantages of a geardrive for a TC-88 engine are there are no chain tensioners to wear out or cause extra horsepower-robbing friction during operation. A geardrive is more efficient than a chain and usually will show a 4hp gain at full throttle.
HB: What effect do bearings have on camshafts?
JA: All engines with cams must have some sort of bearing arrangement for supporting the camshafts. On smaller air-cooled engines such as Harleys, cam bearings are mostly ball- or roller-type bearings, but late Sportsters use bronze plain bearings on all inner camshaft journals. It is important that the cam bearing system on any engine be able to sustain the operational loads for a long running life without deteriorating — serious cam bearing failure usually causes major engine damage.
HB: What is a bolt-in cam?
JA: A bolt-in cam is one that can be installed without modifying pistons, heads, or other engine components. In other words, it bolts in with nothing else to change or alter.
HB: Why is it important to match your cam to your engine performance upgrades?
JA: Matching the cam to other engine performance upgrades is important because too much (high lift and overlap) cam can result in an engine not performing as well as a stock cam. As an example, if a cam designed for a large cubic-inch drag motor were to be installed in a stock engine, the engine would produce less power than with the original stock cam. The reason for this is that cams designed for big, high-output engines hold the valve open as long as possible. This results in less compression pressure than a stock cam, which in turn creates less power than with the stock cam. The reverse of this condition is also true. If a big-inch motor’s cam is too mild, the result is too much compression pressure, again resulting in reduced performance. Matching your cams to overall engine requirements is very important.
HB: Will adjustable pushrods affect a cam differently than solid pushrods?
JA: There is no difference when using either adjustable or fixed-length pushrods, as long as they are correctly installed. The main reason for choosing adjustable pushrods is that they are often much more convenient and easier to install and setup than their solid brethren.
HB: How are the lifters affected by different size camshafts and will an engine need a different style of lifter if the cam is changed?
JA: As for lifters, there is very little reason not to use hydraulic lifters in a Harley-style motor, and H-D lifters are very good units. The only time solid lifters would be an advantage is for an all-out drag bike. Other than that, we haven’t come up with any reason not to use hydraulic lifters.
HB: How is a camshaft made, what is it made from, and are there hardening processes involved to handle the high pressure and revolutions?
JA: Roller camshafts for H-D motors are made of alloy steel, either medical-, bearing-, or aircraft-grade. Commercial-quality steel is just not strong enough for high-speed steel camshafts. Also, our final heat treatment processing is a high-tech procedure that consists of vacuum carburizing. This process yields a very high-quality cam lobe and bearing journal surface second to none.
HB: What makes an Andrews cam superior to other cams on the market?
JA: We think our cams are superior to anything else on the market because we have more experience making H-D cams than anyone in the performance market. We know what to make, how to make it, and what it will work best with. We use the best processing, including material, heat treatment, and finish grinding. We have the best in cam-design technology (we make cam tooling and design cams for many other companies). Our manufacturing equipment is second to none. All our cam manufacturing equipment (cam grinders, bearing grinders, cam milling machines, gear cutters, and cam inspection machines) is fully automated with CNC machines and are state-of-the-art. Our cams are 0.0003 inch within the target data (in other words, 1/10th the thickness of a piece of paper), and five times more accurate than any mechanical camshaft grinder. No one else in the performance cam business can make that claim.
The end result for the builder/rider is a wider selection and the best cams on the market.