There are two physical gears (cogs) for every "gear" in the transmission. One is the "driver" gear and the other is the "driven" gear. Obviously the engine (front) is typically the driver of the motorcycle so the wheel side (rear) of the transmission is the "driven" side.
Each of these gears (cogs) is on their respective shaft (driver/driven) which is connected directly to either the engine (driver) or the countersprocket/wheel (driven).
Constant mesh type transmissions are exactly that. The driver and driven gears are constantly together. The gears themselves never leave engagment from each other. The forks simply slide them over on the driver shaft and driven shaft to engage them.
"Dogs" or "Pins" are the engagement devices. Simple towers protruding from the faces of the gears. These engage into recesses on the adjacent face which is connected to the shaft. Once engaged fully the engine will now drive the wheel in that "gear."
OK...
So really, this thread is all about this engagement.
Lets define some things first.
LOAD - The pressure on the gear teeth, and more importantly, the dogs. Load is developed from the DIFFERENCE between the engine and the wheel. When accelerating or decelerating using the engine, you are creating load. The harder you accel/decel the greater the load.
SPEED OF ENGAGEMENT - The speed of the gear SHAFTS is what's important here. When the driver and driven shafts reach the same speed, THEN engagement is allowed. If they aren't going the near the same rpm, the dogs won't line up with their recesses. The shafts are directly connected to the clutch and the rear wheel.
NEUTRAL THROTTLE - When the engine is neither accelerating or decelerating.
OK OK OK OK...
I can't believe that was just the setup...
The clutch is a tool that releases the load by allowing the driver shaft to freespin with the driven shaft. This makes the load near zero allowing you to shift at any engine speed. The engine is completely removed from the equation.
When you use the clutch to shift to the next gear, whether racing MX or putting around camp, the driver shaft follows the rear wheels speed. This allows engagement. When you re-engage the clutch in a different gear the engine rpm will "match" the rear wheel speed and the engine rpm will be effected either up or down.
When you dip off the throttle and smoothly release the load (neutral throttle) on the dogs, since all the gears ride on the same shafts, the change is linear and has little to no rotation. If you are hard on the gas and dip too quickly or don't dip enough, the gears still have load which grinds away at the dogs depending on the severity of the load.
So, my 24.5 cents is this...
If you properly "neutral throttle" the engine and shift at the most opportune moment, I believe the wear is minimal. I have been doing it for 9 years (25 bikes), and haven't had a bike slip out of gear.
ALSO, I truly believe that you cannot race MX HARD and shift with no clutch and have zero wear. In fact, if you just slammed it over and over without dipping the throttle, I would expect missing dogs. Period.
You rip it off it's ass, expect wear...
I will split the WR in a year or two and we'll see what 57 hp does to a yamaha dog without using the clutch...
-BIG DAN
Each of these gears (cogs) is on their respective shaft (driver/driven) which is connected directly to either the engine (driver) or the countersprocket/wheel (driven).
Constant mesh type transmissions are exactly that. The driver and driven gears are constantly together. The gears themselves never leave engagment from each other. The forks simply slide them over on the driver shaft and driven shaft to engage them.
"Dogs" or "Pins" are the engagement devices. Simple towers protruding from the faces of the gears. These engage into recesses on the adjacent face which is connected to the shaft. Once engaged fully the engine will now drive the wheel in that "gear."
OK...
So really, this thread is all about this engagement.
Lets define some things first.
LOAD - The pressure on the gear teeth, and more importantly, the dogs. Load is developed from the DIFFERENCE between the engine and the wheel. When accelerating or decelerating using the engine, you are creating load. The harder you accel/decel the greater the load.
SPEED OF ENGAGEMENT - The speed of the gear SHAFTS is what's important here. When the driver and driven shafts reach the same speed, THEN engagement is allowed. If they aren't going the near the same rpm, the dogs won't line up with their recesses. The shafts are directly connected to the clutch and the rear wheel.
NEUTRAL THROTTLE - When the engine is neither accelerating or decelerating.
OK OK OK OK...
I can't believe that was just the setup... The clutch is a tool that releases the load by allowing the driver shaft to freespin with the driven shaft. This makes the load near zero allowing you to shift at any engine speed. The engine is completely removed from the equation.
When you use the clutch to shift to the next gear, whether racing MX or putting around camp, the driver shaft follows the rear wheels speed. This allows engagement. When you re-engage the clutch in a different gear the engine rpm will "match" the rear wheel speed and the engine rpm will be effected either up or down.
When you dip off the throttle and smoothly release the load (neutral throttle) on the dogs, since all the gears ride on the same shafts, the change is linear and has little to no rotation. If you are hard on the gas and dip too quickly or don't dip enough, the gears still have load which grinds away at the dogs depending on the severity of the load.
So, my 24.5 cents is this...
If you properly "neutral throttle" the engine and shift at the most opportune moment, I believe the wear is minimal. I have been doing it for 9 years (25 bikes), and haven't had a bike slip out of gear.
ALSO, I truly believe that you cannot race MX HARD and shift with no clutch and have zero wear. In fact, if you just slammed it over and over without dipping the throttle, I would expect missing dogs. Period.
You rip it off it's ass, expect wear...
I will split the WR in a year or two and we'll see what 57 hp does to a yamaha dog without using the clutch...
-BIG DAN
I am. I don't shift either 2nd gear is too fast for me.
kids.....
... where all my reactions are towrds getting out of a jam or ??? like in too high a gear and unexpectedly need a lower one... Other than that... I clutch it! 
..............
May I suggest shifting out of 1st gear?