Although it is gradually becoming less common on modern motorcycles, what generally comes to mind when you hear the word "screw" is probably a Phillips head screw. Phillips head screws are used for assembly in all kinds of situations, but the cross-recessed are surprisingly easy to strip and can be troublesome if crushed. An effective way to prevent such problems is to use a tapping tool.
The screwdriver's cam out from the cross-recessed is the fate of the Phillips head screw.
The countersunk screw in the reservoir cap of the brake master cylinder, which is prone to rusting due to the hygroscopic brake fluid, is one of the most easily damaged Phillips head screws in motorcycle maintenance. After selecting the appropriate screwdriver for the size of the cross-recessed, clean out the rust stuck in the cross-recessed before starting the loosening process.
If the cross-recessed is stripping, the shape can sometimes be corrected by placing a flat pin punch or T-handlebar on the deformed Phillips threaded screw and lightly tapping it with a hammer. If you keep turning with a screwdriver when the cross-recessed is about to collapse, the cross-recessed will wear out and there's nothing you can do about it. If you fix it with a punch, you could have a second chance.
Among the various tools, the screwdriver is the most popular and representative of the items that are known to everyone. Many women don't know what an oil-sealed screwdriver is, but you can say "screwdriver" and they will understand. Many families may have a set of replaceable screwdrivers with a plastic pattern in the living room, just in case something goes wrong.
The reason for the high recognition of screwdrivers is that there are many Phillips head screws around us. Nowadays, many products no longer use screws, but in the past, most assembled furniture was assembled with Phillips tapping screws. The same goes for motorcycles. Today, hex screws with hex holes and Torx screws with petal holes are widely used, but in the past, only Phillips head screws were used for engine covers and around the handlebars.
There is a reason why the mainstay Phillips head screws have been replaced by hexes and torxes. I'm sure many riders have experienced this before, but it's because Phillips head screws are easy to strip. No matter how many times you experience it, the sensation of the screwdriver slipping as the cross-recessed of the screw head strip slipperily as soon as you put in the effort to loosen it is unpleasant.
When using a Phillips screwdriver, it is recommended to use 70-80% force to press the screwdriver against the screw and 20-30% force to turn it. Although the distribution of force is different for each person, even people who have never used tools at all will unconsciously make pressing motions when they hold a screwdriver.
The reason for this is simple: if you don't push against it, the tip of the screwdriver will come off the cross-recessed. The cross-recessed of the screwdriver and the tip of the screwdriver have a tapered angle to ensure smooth engagement, and this causes the tip of the screwdriver to try to pull out along the taper of the cross-recessed when rotational force is applied. This is called "cam out," and is considered a critical weakness of Phillips head screws. So to avoid stripping when loosening, it is necessary to increase awareness of the force of the push.
As with loosening, cam out also occurs when tightening the Phillips head screws. Where this becomes a problem is in the manufacturing of industrial products, including motorcycles. Tightening torque is important when tightening screws, but it is not easy to manage the torque while the driver is trying to cam out. There are screwdriver bits that can be attached to torque wrenches, but the actual torque applied to the screw will fluctuate depending on the amount of force used to push it. This uncertainty is unacceptable for a production site that needs to manufacture a large number of homogeneous products. This has led to the use of hex screws, which are less prone to cam out, and furthermore, torx screws, which have high torque transmission efficiency, have become the mainstream in BMW.
- POINT 1: A Phillips head screw that combines the taper of the screwdriver tip with the taper of the cross-recessed is inherently easy to strip.
- POINT 2: To prevent the screwdriver from lifting up when camming out, focus on the force of pushing the screwdriver when turning the Phillips head screw.
Pushing and turning is the most important, but it is also important that the tip size is correct.
By tapping the through screwdriver, an orthogonal force is applied to the screw, which is expected to strip the adherence of the male and female screws and make them easier to loosen. For screws that have become stuck, it is effective to use a combination of several methods, including anti-corrosion lubricants, heating with heaters, and hammering.
This is also true for bolts and nuts that are stuck.
For the reasons mentioned above, when turning the Phillips head screw, it is important to be aware of pressing down on the screw so that the tip of the screwdriver does not go up the taper of the cross-recessed. This is true not only when loosening screws, but also when tightening it.
Of course, at this point, it is a prerequisite that the cross-recessed and the screwdriver are the same size. Phillips screwdrivers are classified into No.1, No.2, and No.3 size categories according to the size of the tip, and the details are specified by JIS. On the other hand, there are also JIS standards for Phillips head screws, and there are standards for screw diameter and cross-recessed shape and depth.
However, there is a range of tolerance for both standards, and depending on the combination, it is possible for the engagement to become lax. Also, it is difficult to say that some screwdrivers that do not necessarily follow the JIS standards have a good fit with Phillips screws.
Nonetheless, the tip of a No.2 screwdriver will not fit into a No.1 cross-recessed, and if you try to turn a No.3 screw with a No.2 screwdriver, the engagement will be too loose and the screw will rattle. Still, it's amazing how some people try to force themselves to do the work and end up stripping the cross-recessed.
To prevent out-of torque, it is also important to press the screwdriver straight against the Phillips head screw. Depending on the position of the screw assembly, interference with surrounding parts, and the position of the operator, it is common for the screwdriver to be at an angle, but if the screwdriver is turned while it is in contact with the cross-recessed at an angle, the tip that wants to slip will try to slip even more. In order to avoid this, screws installed horizontally must be mounted horizontally. For screws installed vertically, it is important to turn it while applying a pressing force from the vertical direction.
- POINT 1: Be sure to match the size of the screwdriver tip and the cross-recessed of the Phillips head screw.
- POINT 2: It is also important to apply the screwdriver straight to the Phillips head screw and not at an angle.
Penetrating screwdrivers and shock screwdrivers are effective for fixing screws.
This is a mini-type shock screwdriver sold by the tool manufacturer STRAIGHT (The image shows an older model, which has now been replaced by a newer model). Compared to ordinary shock screwdrivers, the body is slimmer and easier to use in tight spaces.
Instead of using even the palm of your hand to grip the screwdriver, use your fingertips to apply the striking force while turning in the direction of loosening. Rather than relying on force to loosen a Phillips head screw that is clearly stuck, it is easier to use against a regular screw to prevent stripping.
The VESSEL MEGADORA IMPACTA can be used as a regular screwdriver and also as a shock screwdriver for screws that are stuck. The grip of a single function shock screwdriver is a metal cylinder, which is not easy to grip, but the grip of this screwdriver is plastic, which prevents slipping.
The cam mechanism inside the grip allows the tip to rotate counterclockwise by about 12 degrees when the rear end is struck with a hammer to loosen the screw. Shock screwdrivers generally have replaceable tips and are not suitable for everyday use, but the MEGADORA IMPACTA is attractive because it can be used as a penetrating screwdriver for normal work.
If the screwdriver shows no signs of loosening even when you push it hard, or if the cross-recessed is blunt, give the screw a jolt as a last resort. The tools that exist for this purpose are called shock screwdrivers and impact screwdrivers.
These screwdrivers have a built-in cam structure that provides a strong rotational force to the tip by hammering the rear end of the grip. Just as a bolt that cannot be loosened with an adjustable wrench can be loosened with an electric or pneumatic impact wrench, it is effective to apply that torque instantaneously to loosen a screw that is stuck, even if the final torque achieved is the same. Even if only a strong rotational force is applied to the Phillips head screw, it will try to escape by camming out, so a shock screwdriver that applies a pressing force by hammer blows and converts that force into a rotational direction is very reasonable.
With the feature of loosening all at once, some mechanics use shock screwdrivers even for Phillips threaded screws that are not tightly fastened, which makes sense. In general, shock screwdriver has its own special shape and function, but there are also products that can be used as regular Phillips screwdrivers on a regular basis and as shock screwdrivers when the need arises.
Even ordinary screwdrivers can be struck with a hammer, as long as the penetrating screwdriver has a shaft that reaches the rear end of the grip. Although the screwdriver does not rotate at the same time as it is struck like a shock screwdriver, it has a similar effect by impacting the screwdriver with a hammer while turning it in the loosening direction to the extent that it does not cam out, making it easier to loosen the firmly attached Phillips head screw. For non-penetrating screwdrivers, the shaft stops in the middle of the grip, so the impact of the hammer is not transmitted to the tip, and in fact, the grip itself may be damaged, so do not hit it.
When loosening Phillips head screws, the first thing to do is to press down hard on the screwdriver, or if it doesn't seem to loosen, use an impact screwdriver if you think you might damage the cross-recessed. Keep in mind that if it is a penetrating screwdriver, hitting the rear of the grip with a hammer to apply impact can be effective.
- POINT 1: Shock screwdrivers exert rotational force through the action of a cam while forcing it with hammer blows.
- POINT 2: Hammering the back of the through screwdriver will help loosen the stuck Phillips head screw.