Coasting bike bad for engine?

[sidewinder]

Yet again been talking to some fellow riders.whilst talking general bike stuff.one old chap was saying that if you coast a bike for to long eg down hill.your engine can be starved of oil.something to do with the way the oil pump works.is there any truth in this.i sometimes coast a lot seems there is just hills round my parts..

[kramdra]

There is little point as it uses more fuel to idle while coasting. If its in gear down hill, almost no fuel is used on a FI bike.

If clutch is in, for cars atleast, it can wear the clutch release bearing quicker. Not really relevant for bikes as it would be easy to change, but still a bad habit.


I no expert on oil pumps. I have heard wheelies can starve the pump of oil and often wonder if it gets enough on side stand or steep hills.

[chickenstrip]

I can't see that there would be a problem on most bikes, as the oil is scavenged from quite low in the sump. I don't know of any models that would suffer from running them on side stand for instance.

Not sure, but there may be one or two particular bikes that were known to have oil starvation problems from wheelying - trying to dig deep in my memory here but none come to mind.

Always willing to be proved wrong on these matters though

[stonesie]

Define coasting?

Some say that it's letting the bike roll down a hill at idle with the clutch in or in neutral, other's say it's simply closing the throttle, I call that over-run.

On a 4 stroke bike neither will cause any damage as the oil pump is driven by the crank and my bike makes some nice popping/crackling on over-run

On a 2 stroke then over-run can be bad as the engine is not getting enough oil through it for the revs that it's doing.

[UrbanRacer]

to the engine, coasting the bike down a hill is no different to a bike sitting still at a set of traffic lights idling.

[Rogerborg]

[Pete.]

[c-m]

IIRC The BMW F800 does not like to be pushed/towed without the engine running, even when in neutral.

Of course that is very different from coasting.

[sidewinder]

[sidewinder]

[sidewinder]

[pinkyfloyd]

[-Monty-]

On my RXS, the oil pump is controlled by the throttle cable as I understand it (i.e. the more throttle used, the more oil is pumped into the engine).

This is all well and good for normal riding; but, if you were to ride it down a hill, in gear and with the throttle fully closed then the engine could be revving quite high (especially if in a low gear). However, due to the throttle being closed, the oil pump would not really be supplying the engine with as much oil as it should. This is what I imagine would be happening based on what knowledge of such things I have.

Perhaps something like this is what the guy was on about.
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Present: [Kawasaki ZX7r][Suzuki DRZ 400s]
Past: [Honda PCX 125] [Yamaha RXS 100] [Honda CB 500] [Triumph Speed Four] [Honda ST1100 Pan European - Po-Po Edition]

[Scythe]

[1cyl]

I thought coasting is only done in neutral?

Surely this is engine breaking being discussed? And my would be on Pete's post.

Doubt any 4 stroke engine, ever made, would suffer under an extended period of high rpm down hill engine breaking (in gear, clutch engaged, throttle closed) but I expect nearly all 2 strokes would.

In response to wheelies, I'd then say this was the other way round, but surely too many variables for both 2T and 4T.
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Chase my Witch up, Catch my Snitch up.
The SMC | The Pit | Stable

[Bloggsy]

[Kickstart]

Hi

Coasting in neutral I don't think a 2 stroke or 4 stroke would care. In gear with the throttle shut down a long hill a premix 2 stroke will get very little oil.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[G]

[sidewinder]

So by reading the recent responses .are we agreed so far the concept is plausible

[G]

On a 4 stroke - no.

As above, the fact that you can go down for extended periods with the throttle shut is the main benefit that I see for a 4 stroke enduro bike.

On a 2 stroke running with premix - it's an accepted concept in some circles as far as going down in gear with the throttle off.

(I wouldn't call this coasting myself, which I would consider to be in neutral/clutch in, which is fine.)

I have wondered whether this would be an issue on a engine driven pump / DI 2 stroke.

[weasley]

There is one scenario that can cause a problem on over-run on a 4T. With the throttle shut there is a very low pressure behind the throttle plate into the engine. If valve stem seals are not in good shape this can pull oil into the engine. However, on a good condition engine this should not be an issue.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[suburban myth]

I'm going to assume that you refer to coasting as 'the bike freewheeling either with the clutch disengaged or the bike in neutral.

On any 4T I generally don't see a problem. If it's getting enough fuel at traffic lights, idling on side/centre stand etc then it'll be getting enough when coasting. If the gear isn't engaged, road speed has literally no effect on engine speed. Imagine riding a bicycle down a long hill. Take your feet off the pedals, let it roll. The wheels, chain and pedals will be going round like billy-o. The engine, (you), will neither have an effect or be affected by how fast the wheels are turning, apart from the obvious - holding on for dear life. Whichever engine or design it is, the oil pump will be turning on a 4T as long as there's fuel going into the cylinder/s.

2T's I reckon are a little more delicate, but overall I think much the same as above - if the engine's idling the there must be oil going into it. The old bugger may be thinking of that 2T Saab James May drove on Top Gear, which in the feature he referred to the engine getting no oil if there was no gas. I don't see how it can be affected on a pre-mix because if there's fuel going in, there's oil going in. On an auto-mix, the oil is fed according to the throttle cable, but surely, surely there must be at least some oil going in when on idle whether there's throttle input or not.

The concept is plausible, but I'd like to see some evidence/hear a few stories.

[Northern Monkey]

[ScaredyCat]

[Northern Monkey]