Starting a Diesel

[nb maggie]

I have previously read in this group some time ago a view that the throttle position when starting a diesel in not important as all 'diesels' start on full throttle until the governor cuts in - I think that was the explanation any way.

 

However, I was reading the manufacturers manual (O.k. is winter, dark and the pub was shut) for the base Lister 'Alpha' engine that is marinised as the 'Canal Star' and fitted to 'Maggie'. It states that if the engine is fitted with a variable throttle (which mine is obviously) this should be fully open for starting.

 

Does any of this stack up.

Edited January 25, 2005 by nb maggie

[bottle]

HI

 

Surely a boat diesel engine is the same as a car diesel engine.

 

When I start my car, have not got a boat yet, the heater plugs are used then turn

 

the key to start, not touching the throttle.

 

There is, I think an automatic fuel control valve i.e. the govener.

 

Of course this only apply to "modern" engines.

 

bottle

[John Orentas]

The point is it doesn't matter, I personally don't think you should not run any engine at full revs. from start up, but some will tell you otherwise.

 

Don't complicate things by thinking about diesel cars, they are fundamentally the same but automated systems can take over for starting.

 

Thought it may be useful to repeat previous response:-

 

"One of the fundamental differences between a diesel and a petrol engine is in the power control system. With a car or motorcycle the accelerator directly controls the amount power that the engine produces by regulating the fuel and air that is delivered, the more you put your foot down or turn the twist-grip the faster you go.

 

A diesel engine is different, it has a speed governor, linked to the engine's injector system. The control lever on your boat effectively determines what speed the engine is to run not the amount of power it produces, a subtle but important distinction.

 

A speed governor is more easily observed on a steam traction or mill engine, a pair of pendulums or bob-weights rotate at near engine speed, as engine speed increases the weights are thrown out-wards by centrifugal force and by a simple mechanism this outward movement controls the amount of steam delivered to the cylinder(s) and therefore the speed of the engine.

 

In a similar way an internal mechanism regulates the amount of fuel delivered by the injector pump to your engine, the action of the bob-weights is opposed by another force linked to the control lever or speed-wheel. So in a very real way you pre-set the speed of your engine which, regardless of the load placed upon it will always try to reach and maintain that speed.

 

When starting a diesel it will run at full power until the pre-determined speed is reached and the governor mechanism takes over control.

 

This is why, when your propeller gets fouled up, it doesn't slow the engine appreciably but you can hear it working harder to maintain it's speed.

 

Have you ever heard a digger working hard shifting earth, the driver isn't controlling the engine, but making the hydraulics put a varying load on the pump which is driven by the engine which is very obviously constantly changing it's power output in response to demand".

Edited January 26, 2005 by John Orentas

[nbtafelberg]

Good explanation John.

 

Just to add if your engine NEEDS you to wind up to full throttle to start something is probably wrong.

[Alastair]

The manufacturer's manual for my Merc engine state that it should be started on full throttle, then throttled back as soon as it fires.

 

Don't know why this is so. I just follow the instructions.

 

So it may depend on the model of the engine.

Maybe it is due to tickover - my engine tickover is very slow, it needs a minute of running before I can drop it back into tickover, or it will cut out.

[nb maggie]

Thats whats my lister manual says as well.

[John Orentas]

The engine manufacturers will always try to keep the operating instructions as simple as possible.

 

I can only repeat, if your your engine starts reliably with the control lever set to half maximum revs. that is the best thing to do.

[Martin]

I think we have hinted at my answer to this - do whatever works mate!

If your particular engine starts first turn with the throttle open but fires then dies with the throttle shut, open it!

(Yes I know the "throttle" idea is irrelevant as there is no throttle, but we know what we mean!).

 

My Lister HRW3 will turn over on the starter for ages and then splutter and finally fire up if your lucky with the throttle closed.

Open it half way and it starts up first push of the button.

In winter, I pull up the governor override plunger which increases the fuel flow just until it fires.

 

Mine therefore does not start on full throttle under governor control.

 

One thing to remember though...

If an open throttle is required for starting, make sure you shut it down as soon as the engine fires - don't wait for the revs to build up!

Engine internals are at their most vulnerable at the 'just started' stage as the oil pressure takes a while to build up - particularly on slower revving machines.

[awatsonbcp]

I think we have hinted at my answer to this - do whatever works mate!

If your particular engine starts first turn with the throttle open but fires then dies with the throttle shut, open it!

(Yes I know the "throttle" idea is irrelevant as there is no throttle, but we know what we mean!).

 

My Lister HRW3 will turn over on the starter for ages and then splutter and finally fire up if your lucky with the throttle closed.

Open it half way and it starts up first push of the button.

In winter, I pull up the governor override plunger which increases the fuel flow just until it fires.

 

Mine therefore does not start on full throttle under governor control.

 

One thing to remember though...

If an open throttle is required for starting, make sure you shut it down as soon as the engine fires - don't wait for the revs to build up!

Engine internals are at their most vulnerable at the 'just started' stage as the oil pressure takes a while to build up - particularly on slower revving machines.

<{POST_SNAPBACK}>

[david and julie]

Nothing worse than a cold engine starting instantly. On diesels with glow plugs I prefer to go straight to start and turn over until the oil light(when fitted) goes out. Then go through the normal glow plug procedure, with the least throttle possible.The engines with heaters on a button rather than the switch were better in some respects. I am curious if the newer direct injection engines will suffer premature wear by their instant start characteristics. But then the oil is better now.

[awatsonbcp]

<{POST_SNAPBACK}>

 

 

the previous owner of my boat which has the lister 3cyl canal star engine told me to have the throttle at 2/3 full throttle position when starting.It worked for him for 25 years and so far it's worked for me but dont ask me to explain how!!!

 

Alan

[David Schweizer]

My engine (an elderly BMC 1.5) will start wilthout any assistance from the trottle in the summer, as we once found out when bleeding the injectors after a filter change - diesel fuel every where!! But in the winter it simply will not start without setting the throttle lever set at about the half way point, once started it can be returned rapidly to fast tick over. I guess everyone eventually gets to understand the peculiarities of their own engine an knows how it behaves under differ=nt circumstances.

[Paul Evans]

My Calcutt BMC 1800 needs half throttle to start smoothly - try it on no throttle and it cuts out very quickly. But I do cut the revs back to tick over as soon as I can. Whatever works is the way to go.