3345 E. 31st Street South, Wichita Kansas 67216

316-682-4781

 

Professional

Service

 Since 1970

FLYWHEELS

          Understanding Cams
 

          Solid or Hydraulic Lifters
 

          Hidden Virtues of the Shovelhead Motor
 

          Shovelhead Oil Pump and Line Routing Example
 

          Shovel Custom Oil Pump and Line Routing
 

          Measuring Connecting Rod Length
 

          Final Drive Ratio
 

          Spokes and Aluminum Rims

 

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Understanding Cams

The cam you are running will have a profound effect on the performance of your motor. This seems obvious, but the lack of understanding of how cams work, and what they do, can rob you of the full enjoyment of your ride.

A camshaft consists of hardened steel "lobes" that are arranged to raise and lower your pushrods, and open and close the motor's valves. Depending on the dimensions of these lobes, the valves will be held open a lesser or greater distance, for a greater or lesser amount of time. The amount the cam's lobes move the pushrods is called "lift", and the length of time the valves are held open is called "duration."

Stock HD cams are designed to provide a modest amount of lift for a factory-specified duration, and the stock design is conservative. It is meant to provide good performance without putting too much stress on the valve train. Without too much danger, however, you can improve the performance of your engine by installing a higher lift or longer duration cam. BE CAREFUL, however, not to install a new cam while your bike is under warranty. It may void the warranty!

There are as many cam designs as there are bikes, it seems. You can get great cams from Andrews, S&S, Crane, and a host of other manufacturers. There are so many options it is hard to make a choice. But you can get a rough idea of what you want if you know how cams work, and how they influence your motor's characteristics.

If you want to ride around town on a Sunday or take leisurely trips in the countryside you may not even want to know what cam you are running. If the bike is stock you will be happy. However, if you want a little better performance you might want to get a little more aggressive. Using the Andrews cam numbers, you might want to run a J grind, an A grind, or maybe a B grind cam. The J grind will give you better power with a smooth idle, and is just a little better than the stock H grind. An A grind will raise your valves a little higher and keep them open a little longer. It can be bolted in without modifying your heads. An AB grind uses a longer duration exhaust to help your motor run a little cooler, and it gives a little more lift, which improves high RPM (high end) power somewhat.

If you have high-lift springs, and your valves have been properly clearanced, you can run a more aggressive cam like the Andrews C grind. This cam is about as tall as you can get, but you pay a price in more frequent repairs. Still, on the drag strip this cam will put out monster power where you want it - at around 5000 rpm on up.

In general, high lift long duration cams are for high power at high revs. The lower lift and shorter duration cams will skew the power curve down so you can get more low end torque at the expense of high-end power. With less aggressive cams you will also have less maintenance, because the springs and pushrods don't do as much work. Less aggressive cams will also give you better gas mileage and a smoother idle. If you use a kicker you will find the bike easier to turn over as well, and because of the increased air velocity you will find the mixture ignites easier.

Don't think that you need to use an aggressive cam if you are running a stroker motor. If you run a stock grind, or a less aggressive performance cam like the A grind, you will still get a power increase simply from the increased displacement. In addition, you will get improved idling because the higher volume of air flowing through a smaller valve opening will create a higher velocity in the carb at low revs. This improves the idle over what it would be if you were running a high lift cam. So don't worry too much about matching the cam to the displacement or compression ratio when considering the use of a lower lift cam with high displacement engines.

IMPORTANT: The DURATION of a cam can be shorter or longer depending on your cam's unique specifications. It is important to keep in mind that short duration cams can contribute to a problem known as DETONATION. Detonation occurs when your fuel mixture explodes rather than burns. The subject of detonation is so complex that a full page or web site would be required to explain it fully, so no attempt to do that will be made here. Suffice it to say that extreme detonation can destroy an engine in ten seconds! A high compression ratio (above 9:1) and/or a short duration (when the valves are kept open a shorter amount of time) can compress the mixture enough to make it explode rather than burn. Normal combustion is not an explosive process. Instead, a "flame front" is generated by the spark plug, and this flame front expands outward, burning fuel and providing energy as it does so. During detonation, however, the fuel explodes, often at the wrong time in the cycle. This puts enormous stresses on pistons and plugs, and can literally blow holes in pistons. Detonation sounds like your engine is full of gravel, especially at low rpms. Detonation can be cured by running the correct high octane fuel, reducing the compression ratio, adjusting for richer carburation, using cooler plugs, increasing the cam duration, adjusting timing, or a combination of these methods.

Using a high lift cam with a stock or lower displacement engine may be an exercise in futility. It is essential to follow the manufacturer's instructions carefully, because cams often require head work in order to keep the valves from coming in contact with each other or with pistons. In addition, special springs, spacers and keepers may be necessary. Unless you are a drag racer, you should get all you want from your motor by running a stock or modest performance "bolt-in" cam.

Tappets

The "valve train" begins with the cam and ends with the valve itself. Along the way many problems can occur. Tappets consist of a tappet body with a small hole in the side that admits oil to the lifters. A lifter is a device that sits within the tappet body and transfers the motion of the tappet body to the pushrod. The tappets are equipped with rollers that rest on the cam lobes and transfer the positions on the lobes upward to the pushrods, then to the rockers, and finally to the valves.

You can run hydraulic or solid lifters. Hydraulic lifters have been stock in HD bikes since 1948. Hydraulic lifters receive oil under pressure (12 to 35 psi) from the engine and use that oil to damp the motion of a small piston that is connected to a pushrod. The small amount of oil in the hydraulic cylinder provides a cushion against shock as well as thermal expansion compensation. As the motor heats up the cylinders and heads expand upward. So does the oil in the lifters. With hydraulic lifters you get increased reliability as well as less wear and tear on the valve train - up to a point.

Hydraulic lifters are just the ticket for average street cruising and touring, but look out when you roll on the throttle and rev that engine! You can exceed the lifter capacity, forcing the oil out of the hydraulic cartridge and possibly damaging your engine. The solution, if you want to push the motor to its limits regularly, is to install solid lifters.

Whether you install solid lifters or convert your hydraulic lifters to solid, you will be able to run a more aggressive cam, and you will be able to twist that throttle as much as you like. However, you will need to adjust those pushrods more often, and you will need to deal with damage due to increased stress on the valve train.

It's all a matter of what you want to do with that bike. If you want to spend time on the drag strip and street riding isn't important, you will want to run a high lift cam, and use solid lifters. In fact, if you run an Andrews 3 grind or an S&S 514 on up (for example) you MUST use solid lifters. If you use your bike on the street or for touring you will want the reliability and decreased maintenance requirements of an hydraulic lifter set.

Shovelhead riders may be interested in upgrading to Jims Powerglide tappet blocks. These blocks are machined to accept Evolution tappets, so you get the benefits of Evo technology, including higher revs and lower maintenance in your shovelhead motor. The kit comes with hydraulic tappets and lifters ready to install. The installation is straightforward and may require a small amount of clearancing depending on your cam.

 

Hidden Virtues of the Shovelhead Motor

The HD Shovelhead motor went out of production in 1984. The motor has always had a bad rep, probably because it was the motor that AMF bought when it bought the company in 1974. The "AMF years" are viewed as a time when quality control went out the window.

But is the bad reputation of the shovelhead deserved? Aren't there some positive reasons one might run a shovelhead motor? First the obvious differences between the Shovelhead and the Evo:

  • Rocker Box: The shovel design contains the rocker arms and shafts in the Rocker box and can be removed along with the head from the engine, where as the Evo design requires removal of the 3 piece rocker box and rocker arms to gain access to the headbolts for head removal.
  • Cylinders: The Evo design uses an iron core encased in aluminum casting where the Shovelhead is cast iron throughout.
  • Headbolts: The Evo uses long bolts that extend from the case to the top of the head, where the Shovelhead uses two sets of shorter bolts - one set to secure the cylinder to the case, and the other to secure the head to the cylinder.
  • There are many other differences, but those presented here are perhaps the most significant. Shovelheads can be constructed to be more powerful and more reliable than any Evo. Many racers prefer the shovelhead because it is easier to modify and capable of tremendous extremes of operation. You can get an incredible variety of specialized parts, including high performance cases, pistons, valves, heads and cams for shovelheads. The engine ain't dead by any means, and is considered by many to be the best motor Harley Davidson ever made.

    In racing applications shovelhead cylinders distort less than Evo cylinders because the shovelhead jugs are made of cast iron. When under extreme stress, Evo cylinders (made of aluminum) tend to change their shape due to unequal stress distribution around the head bolts. This results in "blow by" between piston rings and the cylinder wall, and a reduction in power that gets transferred to the pistons. This is a major reason for the desirability of shovelhead motors in racing.

    Although the Evo has higher tolerances, the Shovelhead can be worked on in a home garage without the need for high tolerancing machine tools. In this respect, the Shovelhead is the last HD motor to be designed for the "farm-hand". You can wrench the whole thing yourself! (With a little experience.)

    The Evolution engine has earned a reputation for being more "reliable." In reality, the Evo is indeed a little more reliable, but a poorly maintained Evo will be much less reliable than a well maintained shovelhead. The difference is that when the Evo gets out of whack you probably won't be able to fix it yourself.

    You don't need to remove the Shovelhead motor from the frame to remove the heads or jugs. This means you can inspect and replace valves, guides and heads as necessary. You can even hone your own cylinders! The Evo may be more "reliable" but it is also closer to the philosophy of "no user-serviceable parts inside." The twin-cam 88 is even less user-servicable. You need lots of special tools to work on any HD motor after the introduction of the Evo.

    So, you may need to change oil more often, and re-torque bolts, and deal with wear in your valve guides, but you can do these things yourself instead of paying an expensive company mechanic. If you are of the philosophy that a big part of riding a bike is being constantly, intimately aware of how it is functioning, you may find a good set of tools and a well set up Shovelhead motor is just the ticket. Bottom line is what you do when you are stuck by the side of the road and can't take anything apart with limited tools. Evo riders wait for the tow truck. Shovel riders can unbolt stuff and make repairs.

    Shovelhead Oil Pump and Line Routing Example

    Shovel Custom Oil Pump and Line Routing

               Measuring Connecting Rod Length

    Rod length is defined as the distance between the center of the piston pin to the center of the crankpin. Obviously, finding the exact center of a hole is very difficult.
    Try this method:
    Grab a set of calipers and measure the distance "A" between the inside of the holes. Then measure the distance "B" between the outside of the holes and calculate Rod Length = (A+B)/2
    The values for this example: A = 6.233"  B = 8.642" ...... Rod Length = (6.233+8.642)/2 = 7.438
    This is a very common Harley Rod Length rated at 7.440 inches.

     

     

    The Final Drive Ratio

    Find that you just can't get good gas mileage no matter how you adjust your carb? Does your stroker need to be revved up to 4000 rpm just to go 75 mph? You may need to take a look at your Final Drive Ratio!

    The Final Drive Ratio (FDR) is the PRODUCT of the ratios of your primary drive sprockets (or pulleys) and the ratio of your secondary (or final) drive sprockets (or pulleys). In a formula, this can be expressed as (T/E)*(W/C), where T is Transmission sprocket circumference, E is Engine sprocket circumference, W is rear Wheel circumference and C is Countershaft circumference. Each circumference is measured in sprocket or pulley teeth.

    Given a typical setup, the stock configuration is usually very near 1.5 for the primary, and around 2.2 for the secondary. The FDR for a stock bike might be around 3.3. But wait a minute, you're running a stroker motor. You should know that you don't want to run anywhere near redline, which happens to be at 4,500 rpm. You want to stay below 4,000 rpm to avoid unusual wear and tear (like leaving aluminum on the walls of your cylinders). A stroker wants to run with about a 2 ratio for the secondary. This means a FDR of about 3. This way you will keep the revs down and make use of all that torque. For a typical setup you will be revving at about 2500 rpm when going 60 mph. Now, these numbers are highly general, and depend on lots of factors, not least of which is the diameter of your rear wheel.

    Be CAREFUL not to get the FDR much below 3.0, as this will put too much stress on the drive train components.

    A 10% decrease in the FDR may translate into about a 10% increase in your gas mileage, but not necessarily. Turns out that the energy required to move your bike is the same regardless of what your drive ratio may be. What this means is that the fuel that is burned will be about the same to go a given distance, no matter how much mechanical advantage you obtain. However, there will may be SOME change in your gas consumption. It really depends on the changes you make to your riding style based on the new sprocket ratio.

    Spokes for Aluminum Rims

    When you want to run aluminum rims, you need to be aware of problems that can occur due to the use of dissimilar metals.

    Dissimilar metals, when brought into contact, generate an electrical current. The current comes from electrons that are present in dissimilar quantities in the atoms of the two dissimilar metals. Especially in the presence of a catalyst (like sea water), electrons will migrate from the material with an excess of them to the material that has a relative electron deficit. In the process, an oxide is formed in the sacrificial material. For example, aluminum will rob electrons from iron and create aluminum oxide and iron rust. The chrome on your spokes will flake off.

    When you run aluminum rims you MUST install stainless steel spokes! If you don't, you will find those spokes turn to rust very quickly, with potentially disastrous consequences. The stainless steel spokes cost about thirty bucks more than their chromed iron counterparts, but this cost is minor compared to the cost of a failure of a spoke, a punctured inner tube, and a potentially fatal crash.