What is engine stop?

stonemonkey · Post by **stonemonkey** » Tue Dec 02, 2008 1:15 pm

So I have been reading lots about diesel bikes, and trying to get a handle on performance. Something that keeps coming up is engine stop on a diesel bike.

My guess is that unlike a petrol, when you throttle off, the bike doesnt necessarily slow down that much. For example when you come to stop lights.

Does this mean then that you tend to mash the brakes a lot?

Would adding larger front and rear disc brakes be a good option?

Would a cvt be better than a normal gearbox for this problem because the cvt automatically cuts out when you drop below certain revs or brake?

arnaud · Post by **arnaud** » Tue Dec 02, 2008 3:48 pm

Hi, normally the engines have a idling rpm which can be set in by your choice. i don't understand your question really, when you want to slow down, you release the throttle,.. and, if neccesary, use the brakes and cluctch of your bike..
Whats the problem?

Post by **Dan J** » Tue Dec 02, 2008 4:08 pm

If I'm right about the question, it centres on the fact that a diesel has no ignition and will continue to run if fuel is provided. Therefore on the more simple engines (that don't have a electrically operated solenoid or similar) you have some form of "engine stop" to cut fuel flow and stop the engine.

stonemonkey · Post by **stonemonkey** » Tue Dec 02, 2008 4:16 pm

sorry I used the wrong wording it should be engine braking not stopping.

Ihave posted a link to the article talking about the klr military motorbikes and he mentions engine braking.

http://www.motorbikestoday.com/features ... _bikes.htm

Post by **Dan J** » Tue Dec 02, 2008 6:00 pm

I get the levels of engine braking I'd expect from a petrol out of my Yanmar clone and I think that's pretty usual.

Post by **Fiddler** » Tue Dec 02, 2008 7:35 pm

I got a reasonable amount of engine braking from a twin diesel. Probably not as much as say a high compression single cylinder petrol, but certainly as much as say an inline triple or four cylinder petrol.
You get engine braking with CVT, until the revs fall to the point where the clutch disengages. The better you tune the engagement of the clutch the better it is, otherwise you end up coasting for a short distance to a stop. Decent brakes are useful then.

Cheers, Mark

sbrumby · Post by **sbrumby** » Tue Dec 02, 2008 8:24 pm

Yes its true there is no butterfly valve in a diesel but with 19/1 compression you certainly get engine brakeing in fact with the big flywheel you get more than a petrol bike. Think about a car you would be hard pressed to tell the difference.

Post by **Stuart** » Tue Dec 02, 2008 11:05 pm

I always thought I got less engine breaking because there was no carb slide blocking air from going in. And that big flywheel would like make me run on forever

oldbmw · Post by **oldbmw** » Wed Dec 03, 2008 12:12 am

Stuart is correct.
diesels have less braking action because there are no pumping losses. ie the power used to compress air is released when it expands, It also mostly account s for diesels in bikes not needing forced air cooling. When at high revs moving the air flows over the engine, at idle, stopped a diesel produces much less heat than an equivalent petrol engine because of the lack of pumping losses. A diesel idling also uses a lot less fuel because of this, it also uses a much leaner mix idling, nearer 200 to 1 compared with petrols 14 to 1. ( under load it nearly catches up.)

arnaud · Post by **arnaud** » Wed Dec 03, 2008 1:17 pm

okay, now i get it. the 'throttle' is regulated with a governer, which, in most cases will be managed by your right hand

My enfield with 418 single diesel brakes a lot more when i close the thtrottle then an original enfield 500 petrol.
Braking paddings last much longer

So, a gearbox tranny is allright.

Nanko · Post by **Nanko** » Wed Dec 03, 2008 1:42 pm

arnaud wrote:My enfield with 418 single diesel brakes a lot more when i close the thtrottle then an original enfield 500 petrol.
Braking paddings last much longer
So, a gearbox tranny is allright.

Same experience here , the 1527 ccm fourcilinder diesel brakes a lot more compared to the original 850 ccm petrol twin.
Cannot explain why , as old BMW mentioned " no compression loss"
I know trucks use sometimes a manually operated valve in the exhaust to improve "engine braking"

Maybe there is compression loss due to expanding air by the compression only ?

sbrumby · Post by **sbrumby** » Wed Dec 03, 2008 8:10 pm

My 950 brakes just fine better than any petrol I have ever rode. What has been written is all good in theory but the fact is its easier to push a petrol than a diesel.

andrewaust · Post by **andrewaust** » Thu Dec 04, 2008 10:53 am

Hey guy's

Engine stop:
Yes a electronic fuel cut off solenoid works a treat if you put it close to the injection pump, you can also put a solenoid or cable setup to close the governor rack to cut fuel. Simply turning off the fuel cock is usually not a good idea as you'll get a vacuum in the line, if air can get in you've got a problem.

If you want to get the electronic solenoid, one place to go is a garage that install gas conversions on vehicles, grab the fuel cutoff solenoid from them. Solenoids are getting harder to get hold of due to many cars now being fuel injected. Put one wire to ground, the other to either your ignition or better still the engine stop switch! On some bikes current is supplied to the coil like the Enfield, so moving the stop switch to the off position kills the power.

Engine braking:

You will get more engine braking from a butterfly valve in the inlet or the exhaust if using it as a braking device only.

The reason why you don't get much engine braking from a diesel is the air that is getting compressed actually bounces the piston back down, that is why jakebrakes (Jacob brake tm) works by releasing the compressed air on top dead center of the compression stroke.

Two stroke petrol engines are also horrible things for engine breaking

Jakebrakes in action

http://www.youtube.com/watch?v=BIcBubwDaaU

stonemonkey · Post by **stonemonkey** » Thu Dec 04, 2008 12:29 pm

so if i understand this correctly. If i added a butterfly valve similar to a car or motorcycle it would help to slow me down more effectively. I imagine installing it just behind the air intake would be best.

wouldnt that then require 2 throttle cables? one to the engine and one to the butterfly valve.

sorry im new to all this (diesel engines) so i will probably ask/make stupid comments.

Post by **Dan J** » Thu Dec 04, 2008 1:30 pm

Stonemonkey - diesels by virtue of their design operate with maximum air intake. This is what is compressed to ignite the fuel and under no circumstances would you want to throttle this. Revs are altered simply by changing the volume of fuel injected. As most of the comments here state, engine braking is of virtually no concern - a bike fitted with a diesel engine is not going to keep going when you close the throttle, it'll slow down just like any other engined bike much as you'd expect.

My 10hp Enfield has drums front and rear and it copes perfectly fine with that. If you want sports bike levels of braking you need disc brakes and probably don't want a diesel bike in the first place - but either way this is not something you need to worry about...

Dan

Nanko · Post by **Nanko** » Thu Dec 04, 2008 3:22 pm

I just measured braking effect on my diesel aircompressor .
No load from the aircompressor , starting on the same engine speed I measured deceleration by: only the fuel pump off , and next fuel pump off AND intake fully closed.
Both situations took 10.5 seconds before engine fully stopped.
Blocking the exhaust will have more effect , because pressure builds up much more than the 1 Bar vacuum in the intake

DieselBike.net

What is engine stop?

What is engine stop?

wrong word engine braking not stopping