Current dirt bike engines are truly mechanical marvels that offer extremely high-end performance to every dirt rider. These engines push the limits of performance and weight with complex castings and assemblies that require careful adherence to all factory torque values. Nowhere is this truer than with the four-stroke top end and valvetrain. Actually, the necessity for using a torque wrench existed when we all rode two-strokes, but most garage hacks simply trusted in the “calibration” of their elbow. It’s extremely easy to warp reed blocks and cylinder heads, and it’s even possible to warp a cylinder base when correct torque values and procedures are not used. In aerospace applications torque wrenches are calibrated virtually before every use; and if a wrench breaks or otherwise loses calibration, every fastener touched by that wrench must be done over, and those do-overs can run into the millions of dollars! The price tag for ignoring torque values on a dirt bike aren’t of the same magnitude but can be very expensive. There are quite a few choices for torque wrenches today, so we’re describing the various options available and providing some simple care tips that will keep your wrench working as it should.
01. The cheapest and toughest sort of torque wrench uses a flexible beam and a pointer. It has few parts, and if the pointer gets bent, it can be bent back to “zero” the tool, and it will still work. Sears, for example, offers a lifetime warranty on the beam and pointer wrenches but not on other types. You should never engrave or etch on the beam, and it shouldn’t even have stickers put on it. The beam-type scale can be difficult to read in tight situations, and it is critical that you pull smooth, straight and level on the handle. Otherwise the pointer can rub and affect the reading. This is the least accurate type of wrench for light torque settings.
02. The most common torque wrench style today is an adjustable micrometer type. “Micrometer” isn’t a comment on the accuracy, but the fact that the torque setting is set by twisting the handle until it reaches the correct mark on the barrel of the tool. Rotating the handle clockwise tightens a spring inside. When you torque a nut or bolt, the tool “clicks” to let you know the correct torque has been reached.
03. Dial-type torque wrenches are generally considered to be the most accurate type of torque wrench. The dial-type wrench is the only type of torque wrench where the final reading is not easily affected by the hand-hold position on the wrench. These tools are wider than some of the other types so may be difficult to use in tight situations, and the dial scale may be impossible to see.
04. Finally, there are split-beam click wrenches. The wrench has few components, and there is no need to work the wrench in before using it when new or after extended storage. The adjustment mechanism is not under a load, so there’s no need to return the tool to the lowest setting for storage. These wrenches are recognized by their push-button adjusters in manual or digital.
05. Most of these torque-wrench styles are available in different ratings and scales. The American scales are inch-pounds and foot-pounds; Newton meters and meter-kilograms are also common. Most motorcycle shop manuals have each torque reading in multiple scales to suit most wrenches. Various drive sizes are common with 1/2 inch being most common followed by 3/8 drive. The 1/4-inch drive is the least common but is almost a requirement for modern valvetrain fasteners.
06. Keep the case the wrench came in, and store it in the case. For a micrometer type, store it with the scale at the lowest setting. Don’t allow any sort of liquid to get inside the tool, and wipe the exterior of the tool frequently to keep it clean. Some models even come with a small, moisture-absorbent pouch in the case.
07. Always pull the handle in a smooth arc with the pull 90 degrees to the handle. Don’t pull down or up on the handle at the same time, and don’t jerk the handle. Dropping the wrench or keeping it loose in a drawer where other tools are banging into it can affect the calibration of the unit. Obviously, if the wrench requires this much care, never use it as a hammer or a pry bar. Don’t ever put a “cheater pipe” over the handle, either.
08. Torque wrenches are most accurate in the center 60 percent of their range. So a wrench rated for 20 to 100 foot-pounds (ft-lb) is most accurate between 35 and 85 ft-lb. Figure out what torque the majority of your work is at, and buy the correct wrench. If you’re serious about your work, you’ll most likely need two or even three wrenches to hit all the common fasteners on a dirt bike.
09. Many torque wrenches are designed to work in one direction only, and some will void the warranty if you use the wrench to loosen a tight nut. Even when a wrench is designed to use both directions, it is to torque right-hand and left-hand threaded nuts and bolts, and not to use as an ordinary ratchet. Using more force than the rating-for example, tightening a bolt to 110 ft-lb with a 100 ft-lb wrench-will damage the tool.
10. Every company and expert agrees your wrench should be calibrated from time to time. For sure if it has been dropped or you suspect someone has used it improperly. Also, if you just get the feeling it is off. Finding a place to calibrate it is a different matter. If you have Mac, Snap-on or similar professional tools, then you shouldn’t have much trouble. Snap-on’s Western Service Center said the average calibration charge is around $60. Every company I checked required shipping your wrench to them. Sears claims every store can send in your Craftsman wrench. At my local store the guys in the service department looked baffled when I asked about the service. The quoted price was $90, so it would be about the same as buying a new micrometer-style unit. The calibration is a good deal if you have a more expensive push-button, split-beam-type wrench.
11. My wrench is claimed to be good for 5,000 uses before calibration (if taken care of), so you start to see the wisdom in caring for the tool. Cheaper off-shore wrenches may be difficult to calibrate, and you may not find a company willing to do the work. Also, just because a tool says it is has a certain range does not mean it’s certified. Make sure the tool you buy is certified, so that at least it starts out accurate.
12. If a micrometer-type wrench has been stored for a while, put the scale in the middle of the range, then find a bolt tighter than that range-a rear axle nut, for example-and click the wrench four or five times to free it up. Then set the desired torque and begin your work.
13. For every fastener, check the manual to see if the threads should be dry or lubricated. Some fasteners call for dry threads but lubrication on the washer surface; others want the threads lubed.