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| + | ====== REF: Service Procedures 11D ====== | ||
| + | ====== What Causes the 1991-2003 Shift Drum Pins to Walk Out of the Drum ====== | ||
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| + | **When you engage the shift pedal, the shift shaft is repositioned in it's bushings to the end of it's clearances (designed or constrained)**. \\ | ||
| + | That begins the angle that the shift arm will turn. When the shift pawl grabs a pin, it pulls toward it's center axis at the shift arm. \\ | ||
| + | That center axis is on a varying side to side angle. The shift arm rotates vertical to the shaft axis. \\ | ||
| + | The shift pawl is also vertical to the arm but doesn' | ||
| + | The flat planed pawl is allowed to move fore and aft of the arm due to a loose clearance between the spacer washer and the pawl retaining ring. \\ | ||
| + | In any up or down pull position of the pawl, the exact angle of pull will be different than the last pull. \\ | ||
| + | The pawl is allowed to flail inward and outward on it's own by gravity until it is engaged to a pin. \\ | ||
| + | The angle of pull on a pin can be rearward, centered or forward toward the left side of the bike. \\ | ||
| + | The pawl hook grabs a pin and pulls up or pushes down in a rotating direction while changing the geometry of the shift shaft (angle of pull). \\ | ||
| + | If the pawl angle exceeds the designed clearance at the arm, the connection at the arm stiffens and the pawl becomes a rigid extension of the shift shaft. \\ | ||
| + | |||
| + | **Shift drum endplay also has a roll in the angle of pull from the pawl also**. \\ | ||
| + | The pawl will pull the drum out or in (depending on the current drum position as opposed to the current pawl push/pull direction). \\ | ||
| + | So when the pawl grabs a pin, it actually moves the shift drum sideways during that throw. \\ | ||
| + | Shift fork and transmission gear movement will also move the drum sideways as will vibration. \\ | ||
| + | In fact, you can stand the bike upright, slap the seat and the drum will move sideways. \\ | ||
| + | The act of leaning into a curve will also move the drum (if it's not already moved in that direction to extreme end). \\ | ||
| + | |||
| + | | Shift drum end play ((photo by Hippysmack)) | ||
| + | |{{: | ||
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| + | **There is plenty of clearance in the arm to pawl connection to allow the angle needed to keep the pawl from being pushed on the pin(s)**. \\ | ||
| + | When the drum slides either way, the arm (should) stay in alignment based on it's varying constrained forces acting on it. \\ | ||
| + | However, the pawl is designed with much clearance which allows compensation for changes in drum endplay and shaft play. \\ | ||
| + | So the angle of the hooks and shaft arm should not affect the amount of torque or throw on a pin to complete a shift action. \\ | ||
| + | |||
| + | **Shift drum pins were not meant to move but due to quality control, construction, | ||
| + | Heat and vibration are secondary contributors but without the heat, vibration will not pull a pin out. \\ | ||
| + | If the shift arm / pawl turns outward during a shift, the drum is also pulled outward at the same time it is being pulled up or down. \\ | ||
| + | Sometimes when the pawl is grabbing a pin and moving the drum, a pin will be in the right condition to be weak in it's pressed in tightness. \\ | ||
| + | Normally, the pawl will pull the pin including the weight of the drum and any forces acting on it (shift forks and moving transmission gears). \\ | ||
| + | However, if a pin's press fit gets weak enough, the pawl will pull the pin out of the drum instead (pin lets go of the drum). \\ | ||
| + | The pin's press fit is weakened by heat. Vibration gives a weak pin joint a push and the pawl grabs and snatches the pin out. \\ | ||
| + | If a drum pin is hot enough and subject to moving, the math is pretty easy from there. \\ | ||
| + | When you see two or more pins that have moved, then that many pins were subject to be in that condition. \\ | ||
| + | And they each individually let go when the condition was ripe (may or may not be consecutive shifts but won't be at the same time). \\ | ||
| + | And they won't necessarily come out of the drum at the same lengths. \\ | ||
| + | A momentary thrust from the quick act of a gear shift, then the shifter is dormant until the next shift is done. \\ | ||
| + | Meanwhile, a pulled out pin then " | ||
| + | Due to shift drum endplay, a "shift ready" pin can technically be shifted outward or inward (L or R sitting on the bike). \\ | ||
| + | So it is possible for a pin to pull out a few thousandths and later be pulled back in a few thousandths depending on the angle and condition at the time. \\ | ||
| + | If the drum is already shifted forward and the force from the shift arm moves further forward, a pin not quite ready can go ahead and move. \\ | ||
| + | The full weight of the pawl movement is on the pin at that point. \\ | ||
| + | |||
| + | **Due to design and / or construction, | ||
| + | And it can happen to any 91-03 Sportster. \\ | ||
| + | The drum pins are not a full bodied press fit (the pin OD is smaller than the hole they go in). \\ | ||
| + | The pins are spiked in a few places in circumference and the spikes create the interference to keep them in place. \\ | ||
| + | (3 small bulges of metal protruding at the end of 3 small grooves in the middle of each pin) \\ | ||
| + | These small bulges are not enough to keep the pins in place during extreme conditions. \\ | ||
| + | But they are forgiving enough to keep them midway in their holes after protruding, creating that side force on the detent plate. \\ | ||
| + | If the pins were a full body press, they probably wouldn' | ||
| + | But then again, one has to ask if it's poor pin construction or thermal expansion of the shift drum holes. \\ | ||
| + | However, if it was the drum getting too hot, all the pins would be subject to walking out. \\ | ||
| + | |||
| + | |Example of pins pulled out on of xLoneRiderx' | ||
| + | |{{: | ||
| + | |||
| + | **Heat testing was done on the shift drum pins below**. \\ | ||
| + | In the third pic below, heat was applied to the old shift drum to find what operating temps may be when a pin pulls out. \\ | ||
| + | At ambient temp, none of the pins would turn or move being clamped in vicegrips. \\ | ||
| + | The drum was clamped in a vise, heat applied to it with a propane torch and the heat from the drum was measured with an infrared thermometer. \\ | ||
| + | At various temps (197°F, 207°F and 242°F), all the pins were clamped with an attempt to turn them and only 1 of them ever moved. \\ | ||
| + | Coincidently, | ||
| + | Anywhere before and after the 200° mark, the one pin could be turned. \\ | ||
| + | So that is the heat range where that certain pin will no longer hold. \\ | ||
| + | The other three pins took 242°F but did not move. So it appears it's not just heat that makes the pins move. \\ | ||
| + | It's a combination of heat, pin fit, vibration and how much of a pull or thrust the shift pawl gives outward that makes the pin(s) walk out. \\ | ||
| + | Some press fits are tighter than others especially if speaking of how tight the spikes on the side of the pins are. \\ | ||
| + | Either some of the spikes (or bulges) are made taller on some pins than others or they get squashed more than others by the original installation. \\ | ||
| + | So it appears it's construction, | ||
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| + | |Heat testing the pins ((photo by Hippysmack))| | ||
| + | |{{: | ||
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| + | **Some have tossed around ideas on redesigning the pins and / or the spring clip that holds the detent plate to the drum**. \\ | ||
| + | One idea is to weld the pins to the drum. \\ | ||
| + | However, the load is going to happen any way due to construction and clearances up stream of the pawl (and pin movement is actually a symptom and not a cause). \\ | ||
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| + | [[: | ||
