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Over rev vs engine braking

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Do these situations occur at the same time? If, when accelerating at the top of gear, you let off of the throttle and experience deceleration due to engine braking are you not also in an over rev scenario?

I ask because I routinely ride wide open fire breaks on my YZ450F and spend a lot of time in 5th. When letting off of the throttle I experience some engine braking. I am concerned that I may be accelerating engine wear by doing this routinely.

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26 minutes ago, Yama11 said:

Do these situations occur at the same time? If, when accelerating at the top of gear, you let off of the throttle and experience deceleration due to engine braking are you not also in an over rev scenario?

I ask because I routinely ride wide open fire breaks on my YZ450F and spend a lot of time in 5th. When letting off of the throttle I experience some engine braking. I am concerned that I may be accelerating engine wear by doing this routinely.

Engine brake is not the same as mechanical over rev. What you're describing is fine. Mechanical over rev is when you make the motor spin faster than its meant to. So if you were at the top of 5th and down shifted to 3rd, you'd be in over rev territory. On something light, like a dirt bike, the rear tire typically locks up instead of allowing the motor to over rev. 

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Just to say what has already been said in a different way that might help the light bulb go on...

When you are cruising over flat ground in 5th gear, you are still at a safe RPM by definition since the rev limiter would have kicked in and prevented you from accelerating past a safe engine speed.  When you shut the throttle you are engine braking, slowing down and the revs are falling.  Because you were at a safe engine speed when you began engine braking and because engine braking causes the bike to slow and revs to fall, you are by definition always at a safe engine speed during the entire engine braking.

To get a mechanical over rev you'd need to down shift to a point that when you let the clutch out the biker's speed would force the engine to spin faster than it's designed to.  The rev limiter cannot stop this because it's not the internal combustion of air/fuel that's causing the excessive engine speed, but rather the bike's momentum.  As other's have noted with a light dirt bike in low traction dirt, you can get lucky and the tire will lock up instead of forcing the engine to spin faster than designed.  But if there is enough traction due to the surface or the load on the tire (landing a jump, etc) you will over rev it so it's best to be as careful as possible when downshifting multiple gears.

Doc

 

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Overrev will kill your engine :naughty: they like alitte load atleast.  I'd say shift but you're in 5th already. Totally different from engine breaking in 5th 

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I would not ride down a road pinned in 5th for long periods. Even though it is not in overrev, it is hard on the motor, just back off a couple mph.

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