Is Engine Braking Bad For Your Motorcycle The Shop Manual
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TechTranscript
00:00There's a lot of confusion and misunderstanding out there
00:03about engine braking.
00:05So today on RevZilla, I'll explain what engine braking is,
00:07how it works, and whether it's a bad thing
00:09or perhaps even a good thing.
00:11Let's open up the shop manual.
00:20Okay, so engine braking.
00:22Engine braking is the process
00:23by which you close the throttle
00:25and you allow drag in the engine
00:27to slow the motorcycle down.
00:29Here's how it works.
00:30When you're rolling down the road and the throttle is open,
00:33the throttle bodies, which are behind the cylinder here,
00:35are also wide open.
00:36So fuel and air easily passes into the cylinder
00:39as the piston moves down on the intake stroke.
00:42That can be a little abstract,
00:43so why don't I give you guys an example
00:45of what that actually looks like.
00:46All right, so this is a throttle body.
00:48Granted, it's only one.
00:49It's off a single-cylinder engine.
00:51The MT-09 here, obviously, is a triple.
00:53So it would have three of these, but you get the point.
00:55When the throttle is open,
00:57you've got a nice, wide-open bore.
00:59Obviously, the fuel and air
01:00is going to pass through that easily,
01:01but when you close the throttle,
01:03that throttle plate snaps closed,
01:05but the piston is still trying to do its thing.
01:07It's still moving down on the intake stroke.
01:09It's still trying to pull air and fuel into the cylinder,
01:11but it can't because it's doing it against a closed tube.
01:14So you get a lot of intake vacuum,
01:16and that vacuum puts drag on the piston,
01:18which slows it down,
01:20and that, in turn, slows down the rear wheel.
01:23So the big question is, is it bad for your engine?
01:28And the answer is no, not in the slightest.
01:32I can understand where the concern comes from, though,
01:33right, because engine braking
01:35makes the motor sound strained,
01:37but unless you have downshifted to a gear
01:39that's going to cause the motor
01:40to rev up into the red line, no harm is being done.
01:44The first area of concern is a lack of lubrication.
01:49However, when you're engine braking,
01:51it is the throttle plates that are closed.
01:53It's not the oil pump that has been shut off.
01:55It's still operating.
01:56It is still pushing oil through the filter,
01:58still distributing oil to the piston,
02:00to the cam in the top end,
02:01to the transmission in the clutch.
02:03There is plenty of lubricating oil
02:05being distributed around an engine.
02:07So with a four-stroke anyway,
02:09lack of lubrication, not an issue.
02:11Ah, but what about a two-stroke
02:13where the lubricating oil is mixed into the gas?
02:17When your engine braking and the throttle is closed,
02:18you're not getting gas into the engine,
02:20so not enough lubrication, right?
02:22Eh, kind of.
02:23The fact is there is plenty of residual oil
02:26in the engine to deal with a few moments of engine braking.
02:30The piston's not gonna suffer.
02:31The crank's not gonna suffer.
02:32Everything is going to be fine.
02:34The only scenario I can potentially see
02:36engine braking with a two-stroke being a problem
02:38is when you are using it to control your speed
02:40during a long descent,
02:42like going down a miles-long mountain pass.
02:45Other than that, it's really not an issue.
02:47And I can tell you that this particular piston
02:49and crankshaft here has been subjected
02:51to lots of engine braking at the racetrack,
02:53and it's got no undue wear as a result.
02:56It just wore out from living a good life.
02:59Next up, engine overheating.
03:03Now, the MT-09 here has a very large radiator,
03:07and it's there to manage and dissipate the heat
03:10that this engine creates when it's being ridden
03:12at full throttle at high RPM.
03:15When you got the gas open,
03:16you're pouring a lot of fuel in the fire,
03:17lots of heat to deal with.
03:18When you're engine braking,
03:20there is little to no fuel being put on the fire.
03:22Therefore, there is less heat being created.
03:24So why wouldn't this cooling system be able to manage that?
03:27Less heat to manage,
03:28even though it is designed to deal with a lot of it.
03:30And frankly, it's the same scenario for an air-cooled bike.
03:33You're producing less heat from the engine
03:35while engine braking,
03:36yet air is still flowing over the cylinders,
03:38still drawing that heat away.
03:39So clearly, overheated engine
03:42as a result of engine braking, not an issue.
03:45And finally, there is the concern
03:47about clutch and or transmission damage.
03:51You'll see that those transmission gears are very robust,
03:54as is the clutch pack.
03:55And these components are designed to handle a lot of force.
03:58I mean, they're intended to deal with all of the torque
04:00of a full throttle start.
04:02So if they can handle that,
04:03why can't they handle a fraction of that force
04:06while engine braking?
04:07It's not an issue,
04:08and the clutch plates and transmission gears
04:10do not care which direction the force is coming from.
04:14Now, even if engine braking isn't bad for your engine,
04:18there is one drawback.
04:19And that is that if you're using it exclusively
04:21to slow down, it doesn't illuminate your brake light.
04:24So drivers behind you might not be aware
04:26that you're scrubbing speed.
04:27And as a rider that has been rear-ended on the freeway,
04:30I can tell you that it sucks.
04:32So I trigger the brakes and check my mirrors
04:34anytime I'm slowing down,
04:36even if I'm just using engine braking.
04:39Okay, so normal engine braking does not impart
04:43any undue harm or damage to the engine in any way.
04:48As a matter of fact, it can actually be beneficial.
04:50For starters, using engine vacuum to slow down
04:53instead of your brakes means that your brake discs
04:55and pads get a break.
04:57It is a small benefit, but it is a benefit nonetheless.
05:01And perhaps the most valuable use of engine braking
05:04is during long descents
05:05when it can prevent your brakes from overheating.
05:08If you open up your owner's manual,
05:09it probably even suggests using engine braking
05:12for that exact purpose.
05:15Then you've got track day riders and racers
05:17and sport riders who rely on engine braking
05:20to scrub speed as they go into a corner.
05:22And it also ensures that the engine is revved up
05:25and in the meat of the power
05:26when you roll on the gas, leaving the turn.
05:29So whether you've been wondering
05:31if engine braking is bad for your bike,
05:33or perhaps you weren't even aware
05:34of what engine braking is,
05:36now you know that it is safe
05:37and it is a useful way to slow down your motorcycle.
05:40♪♪