Why won't this diesel engine start?

[ProDave]

Asking for a friend. Yes I really am (my own boat has a petrol OB)

Sorry details are a bit scarce, I don't even know the make of the engine, but I am after general principles not engine specific details.

Single cylinder diesel engine about 10HP or there abouts.

Today it cranked over, it sounded like it was trying to start and a puff of blue smoke came out of the exhaust on each compression stroke looking and sounding like it was trying to fire, but as soon as you let go of the starter button it might give one more attempt at firing and then stop. In simple terms as if any power produced by it firing is not enough to maintain momentum for the next compression.

He tried priming and bleeding the fuel, something he aparently has had to do often this season, but he thought he had found the leak and fixed that as last try it started without messing about.

So accepting we don't know the engine specifics, what in general would make a diesel engine behave like this? Fuel problem? Compression problem? timing problem? Other?

 

[ColleyV8]

Does it have a decompression lever?

 

[ProDave]

Does it have a decompression lever?

Yes. He usually has to decompress it to get it to spin, has always been thus, then once spinning drop the decompressor and she fires. Now it sounds like it is trying to fire but not well enough.

I believe it is an old engine with no fancy electronics and you stop it by opening the decompressor.

 

[penberth3]

Yes. He usually has to decompress it to get it to spin, has always been thus, then once spinning drop the decompressor and she fires. Now it sounds like it is trying to fire but not well enough.

I believe it is an old engine with no fancy electronics and you stop it by opening the decompressor.

Is the stop control hard over to the "run" position?

 

[MontyMariner]

Does it have a decompression lever?

Or is the Stop via a solenoid?
You could try a short spray with Holts Cold Start to see if it fires a couple of times.
If it does then stops it would suggest fuel starvation.

 

[ProDave]

Decompressor is via a cable, it definitely sounds as expected once you put it to run. I will suggest eezee start or similar.

 

[38mess]

Is it spinning over fast enough?

 

[ProDave]

Is it spinning over fast enough?

Again I don't know the engine well but the owner thinks so and it sounds like I would expect from the times I have heard it crank and start before.

Another possible factor, I asked about glow plugs, this engine does not have any, never has, and it has got colder up here.

 

[Tranona]

This sounds like a Yanmar 1GM 10. Classic symptoms of poor compression the result of poorly seated valves, bore wear or a bent con rod. One in good condition should not need the use of the decompressor except on very cold starts to build up oil to raise compression.

 

[38mess]

Again I don't know the engine well but the owner thinks so and it sounds like I would expect from the times I have heard it crank and start before.

Another possible factor, I asked about glow plugs, this engine does not have any, never has, and it has got colder up here.

Could you fire a hot air gun or blow torch into the air intake, it should start. It possibly has a cold start procedure which your friend is not following.

 

[Poignard]

"He tried priming and bleeding the fuel, something he aparently has had to do often this season, but he thought he had found the leak and fixed that as last try it started without messing about."

Maybe he hasn't fixed it

 

[bignick]

As Penberth says, check the stop lever on the side of the engine has gone back to the run position.
Also, if he has to keep turning the engine over, you should shut the seacock until it fires up, or you could backflood the engine.

 

[AntarcticPilot]

The three essentials are air, fuel and compression. If you've got all three it will work. It sounds like there isn't good compression - the blue fumes are unburnt diesel so fuel is getting to the injectors, and air is unlikely, but check the air filter. Is the decompression definitely off? Have you checked at the engine, not just at the control panel?

It really would help to know the make and model, as that would help people to provide engine specific diagnostics.

 

[Aja]

I know this has been mentioned before, but does the stop control been checked when pushed home something actually happens at the engine?

On an older engine I had this same situation where I thought the stop control was gone but at the embittered the wire was just slipping.

Worth a check.

 

[Aja]

Beaten to it..

 

[westernman]

The three essentials are air, fuel and compression. If you've got all three it will work. It sounds like there isn't good compression - the blue fumes are unburnt diesel so fuel is getting to the injectors, and air is unlikely, but check the air filter. Is the decompression definitely off? Have you checked at the engine, not just at the control panel?

It really would help to know the make and model, as that would help people to provide engine specific diagnostics.

Could also be that the timing is well off.
Has he been fiddling with the injection pump??

 

[AntarcticPilot]

Could also be that the timing is well off.
Has he been fiddling with the injection pump??

Good point. As far as I'm concerned, the injection pump is off limits, as it requires detailed knowledge and precision to work on it. The engineer I did my diesel course with emphasized that a) it rarely stopped engines from running and b) that working on it required specialist precision tools and a very clean environment. The major reason for it stopping engines from running was failure to observe item b!

 

[Aquaboy]

as said before, stop not returning completely.

 

[KevinV]

My ancient digger will do exactly this if the battery is low - I'd try a jump pack on it before anything else.
If the stop button is out there's no fuel to make the puff of smoke.

 

[AntarcticPilot]

My ancient digger will do exactly this if the battery is low - I'd try a jump pack on it before anything else.
If the stop button is out there's no fuel to make the puff of smoke.

There is if the stop control operates a decompressor as the OP states. Not unknown on older engines; the SABB 6-8 hp for one.