Why won't this diesel engine start?

[KevinV]

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.

Ah, okay, learn something new every day

 

[Daydream believer]

Is there a pot to inject oil into the inlet manifold when starting, as in the old listers?
A good spray of light oil into the manifold would help compression as it is sucked in.

I always found in my dumpers & mixers that it was invariably air in the filters & fuel lines & one had to really bleed the system a lot more than one expected. Just because one has cracked off the injector & seen a bit of fuel come out does not mean all the air has been removed.

One should be careful of constant turning over the starter for too many seconds. It could weaken it. Then lack of oomph will prevent the engine firing

 

[ProDave]

Thanks for all the thoughts so far.

Just a further non technical observation, about it sounding like not enough power in whatever firing it is doing to keep it running. We did try opening the throttle while trying to start, which should have meant more fuel, but it made no difference to the results.

And one last thing he said on last start earlier in the week, when it started there was a "bang" from inside the cabin, which it has never done before and he does not know what that was, but the engine ran after that bang.

 

[ChromeDome]

Fuel feed pump.

Had that recently on a Yanmar 1 cyl, very much improved cold-starting.

 

[jamie N]

Is this a well known Fortrose boat?
If it is, then the engine's Diarm's old one which I'm sure is a 1GM 10. It's been a pig to start all summer for the guy, and he's had many attempts at curing it, indeed I believe that he missed the race yesterday because of it.
I've heard about the fault and reckon that it's the rocker box gasket being worn, which is consequently lowering the decompression lever onto the valve stem causing a fractional but significant loss of pressure. This was the issue on my own engine, which by pure coincidence I bought from "G and that boat" a few years ago.
The fault that was described to me has exactly the same symptoms as mine had, which was cured immediately by getting a thicker/newer gasket that raised the decompression lever away from the valve.
As an interim check to see if it is the fault, the rocker box cover can be slackened off, and an attempt at starting made. It only needed my cover to be loosened, not removed to cure/locate the problem.

 

[shanemax]

Yanmar mechanic at SYH had a thumb pump oil can, full of diesel and squirted a couple of jets of diesel straight into the air intake.
This seemed to work quite well.

 

[shanemax]

Before some one says some thing I am not a mechanic so I do not know if this is advisible .

 

[Poignard]

 

[ProDave]

Yes @jamie N that is the boat and the owner. And yes that is where the engine originated from. I suspect your diagnosis is probably right. I will pass on that suggestion.

It sounds like G did not need to change his engine a few years ago he just needed to fix the old one he had then......

G did miss the race, I was due to be his crew, and I ended up getting a ride on another boat so I did get to participate in the race.

 

[bignick]

To get my 2GM20 to start I set the throttle to FULL throttle in neutral, then press the start button. It fires immediately and I reduce the throttle straight away to around 2000rpm. The Yanmar don’t have any glow plugs, so the sometimes need a bit of help when the weather turns colder.

 

[38mess]

In my old sabb single there was a pipe on the head to pump 3 shots of oil down to aid cold starting. It never once failed to start, even on the coldest frosty morning. There was an oil slick behind for a while.

 

[Daydream believer]

I've heard about the fault and reckon that it's the rocker box gasket being worn, which is consequently lowering the decompression lever onto the valve stem causing a fractional but significant loss of pressure. This was the issue on my own engine, which by pure coincidence I bought from "G and that boat" a few years ago.
The fault that was described to me has exactly the same symptoms as mine had, which was cured immediately by getting a thicker/newer gasket that raised the decompression lever away from the valve.
As an interim check to see if it is the fault, the rocker box cover can be slackened off, and an attempt at starting made. It only needed my cover to be loosened, not removed to cure/locate the problem.

There should be a screw with a lock nut on the decompressor that holds the valve down, It can be adjusted to miss when not meant to be engaged.

 

[srm]

Sounds as if the problem may have been diagnosed.
If not I had winter start problems with a 2GM. Eventually a replacement starter motor solved the problem. The original one was spinning the engine, but not quite fast enough. I also discovered that prolonged cranking was not good for the starter motor.

 

[Tranona]

Yes @jamie N that is the boat and the owner. And yes that is where the engine originated from. I suspect your diagnosis is probably right. I will pass on that suggestion.

It sounds like G did not need to change his engine a few years ago he just needed to fix the old one he had then......

G did miss the race, I was due to be his crew, and I ended up getting a ride on another boat so I did get to participate in the race.

If it is indeed a 1GM go back to my post#9. The decompressor is not needed for starting except maybe in very cold weather to turn the engine over and build up oil pressure behind the rings and so increase compression (or rather limit the loss of compression). The recommended starting procedure is 3/4 open speed control lever to increase the amount of fuel injected on start. If the battery is strong enough to turn the engine briskly, fuel is getting to the injector and it does not start then it most likely means there is insufficient compression. These are very simple engines and just need the "big bang" to get them going. if compression is down then squirting oil in through the intake is a temporary fix, but does nothing for the underlying cause which is one of those 3 common problems in post#9 - most likely a combination for an old well used engine.

Take the cylinder head off and all will be revealed. Compression ratio can be checked without removing the head using the procedure in the factory workshop manual, but that only tests for bent con rod which is the least common problem. Most common is leaky exhaust valve and the smoke and bangs is an indicator of this.

 

[Mister E]

A compression test will show if it has a valve burnt out or any other cause that reduces compression.
On this type of engine you will need to remove each injector in turn, then use adapters to fit a pressure gauge ror the reading.
While the injectors are out it would be a good idea to check the spray patern.
A DIY method is to remove one then rig it up so that you can see the tip. With a jam jar covering the injector turn the engine over and observe the pattern..

 

[38mess]

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.

It also needs a good battery to spin it over fast or it will never start

 

[AntarcticPilot]

A compression test will show if it has a valve burnt out or any other cause that reduces compression.
On this type of engine you will need to remove each injector in turn, then use adapters to fit a pressure gauge ror the reading.
While the injectors are out it would be a good idea to check the spray patern.
A DIY method is to remove one then rig it up so that you can see the tip. With a jam jar covering the injector turn the engine over and observe the pattern..

Probably teaching granny to suck eggs, but do remember that the spray from an injector readily penetrates skin and can result in severe dermatitis.

It also needs a good battery to spin it over fast or it will never start

That can, to some extent, be overcome by getting the motor spinning with the decompressor engaged so there is little load on the starter motor, and then disengaging the decompressor when it's turning fast. That worked for me one time when the battery was down.

 

[B27]

It also needs a good battery to spin it over fast or it will never start

Indeed.
Spinning it a bit faster improves the compression because the air has less time to leak past the rings and valves, and the heat of compression has less time to be lost into the metal.

I used to sail on a boat with a fairly old 1GM, a good battery started it on the button, if the battery was down even slightly, it was reluctant.
In Winter, a 5W solar panel was a game changer.
The alternators on some of those old engines do not push out as many amps or volts as a modern unit, it's very easy for the batteries to get low on a racing boat which only gets a 20 minute run to the start line once a week.

 

[CliveF]

Probably not relevant as the fault appears to have been diagnosed by those with greater knowledge than me.
However I was involved with a big 6 pot in Norway and it was reluctant to start even with 2 fully charged batteries in parallel.

Took ages to notice the alternator was seized and the belt was being dragged round it.
Well that and 20 liters of water in each fuel tank.

Good luck with sorting it.

 

[Refueler]

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

That was my thought ... if injection is out of synch .... then that explains the blue 'smoke' as well.