Coasting with the engine off: was I doing harm?

My commute involves a ferry trip, and I have always (for the past two years, anyway) enjoyed shutting off the engine at the ticket booth and then doing a no power coast in neutral down the hill to the lineup. It's about 1km and I have to brake to keep the speed down.

But recently I heard on the Cartalk podcast a discussion about the horrors of towing a vehicle with the driven wheels on the ground, and that made me worry about how I am turning the transmission without any oil pumping around.

I have changed my coast to an engine running but still in neutral, but I wonder: was I doing harm by coasting with the engine off?

David

 

to my understanding, no you didnt. if the bike is in neutral the clutch is disengaged. meaning the transmission is not even turning.

the same with a car if it is in neutral. (towtrucks around here pull your car in gear if they can impound it and make money)

 

now if you cost with the engine off and in gear that could add extra wear

 

im not a transmission expert by any means, but what pump? iv never had to replace a transmission fluid pump? obviously this is somethign inside the transmission.


and dont go off on me, this is a ligitimate mechanical question...

 

Transmission is always turning while the bike is rolling, and oil pump pressure lubes tranny, but i don't think any damage would be done on any short coasting.

 

Squirrel is correct for the most part....ish. It is common in newer and larger bikes to find lube oil circuits in the gear box ,depends on the bike. No matter what you are ok, we have a 16 mile down hill we do several times a year and I have never given it a second thought.

 

If the engine isn't running the transmission isn't getting oil to the bearings. What you're doing isn't going to hurt anything but not a good idea for any real distance. The oil is pressure fed by the oil pump to the shafts in the transmission and that is what lubes the gears as they rotate on the shafts. No oil pump, no lube to the shafts. A wet sump engine is no guarantee that the transmission gears are submerged in oil, just that oil is carried in the engine cavity rather than a separate oil tank.

 

It's my understanding that while the bike is rolling, regardless of the gear it's in (including neutral) that the mainshaft and countershaft are continuously in motion.

While the rear wheel is turning, the chain is moving as well which is spinning the shafts and all the attached gears. The bike being in neutral will prevent the gears from meshing and creating power (or drag in this case). If the oil is filled to the proper level, then in most bikes the transmission is partially immersed in the oil and while it is spinning the gears and external parts are coated as well. The only thing that will not be oiled properly are the internal parts like the bearings and any part that gets its oil via the oil chamber ducts within the bike above the oil line. The oil pump does not turn while coasting in neutral, but then again - neither does the piston, valves or crank for that matter.

Coasting while in neutral with the engine off should not pose any threat to the transmission if done for a short time as you are doing, followed by running the engine afterward. TOWING the bike a long distance while in neutral on the other hand I really wouldn't recommend. Both wheels should be off the road when towing. The tires, chains and sprockets only give a certain life to begin with, so it wouldn't make sense to tow with the rear wheel contacting the roadway anyways. As I said, even in neutral you are still turning multiple components that are exposed to high wear and designed to be replaced.

As far as comparing to an automobile transmission, you really can't. They are two completely different systems doing the same job from different points of view.

 

Also known as a Torque Converter. This isn't unique to automatics though. I know that on my buddies F350 (2001?, manual, 4x4) you do not want to flat tow the vehicle because it won't pump oil through the transfer case and it will burn up.

-Jake

EDIT: Just checked. This appears to have to do with the transfer case rather than the transmission. Edited post to reflect this.

 

is this bad for your engine squirrelman?

when goign from a fast speed to stopping, or even a slow speed. slowing down in 6th gear, then after being stopped shifting to 1st. it seems that if i do this i have to let the clutch out partly to shift between gears.

what i try to do instead is shift down at the speed i would normally be in for each gear, even though im holding in the clutch the entire time.


(is this a good enough for you tinkerinwithstuff? or is it an inane question)

 

i guess i have more to learn about torque converters. i didnt know the fluid was transmission fluid exchanged with the transmission. but iv never really done much transmission work.

 

Thanks everyone, but I am still confused. If the gears/bearings are in an oil bath, I am okay. But are they in said bath? Or does the engine running pump oil to some bits?

 

listen to squirrelman, he knows his stuff real well. very respected around here.

 

The 6th gen shop manual shows "oil jets" that I assume spray oil in a "blanketing" fashion for the gear teeth, shift drum and shift forks. I also remember that my old CB450 ('74?) had oil passages to the mainshaft and countershaft bearings, as does the CB1100F. Where I'm ultimately going with this is that I personally would not coast for very long, even in neutral, without the engine idling. Most, if not all, bearings in manual transmissions are ball or roller, so they don't need nearly as much oil as engine plain bearings (crankshaft and rods). But they do need a constant oil supply to stay healthy while they are rotating. I would think that an occasional short coast with the engine off would be tolerable, but once a rolling bearing element is damaged, it goes downhill pretty quickly. The localized bearing damage is bad enough, but what makes it worse are all the little bits of metal that start finding their way in between gear teeth, which load the bearings even more, which accelerate the wearing process, etc.

I would counter the above, to some degree, by stating that modern lubricants and metals are incredibly resilient compared to what was commonplace 20 years ago. Odds are that your transmission is fine, especially if there are no funny noises or other noticeable problems. I just like to err on the side of caution.