Engine seems to start but rolls to a stop

[JustinT]

Hi all
I have been fiddling with my engine for months now, its s Bukh DV20.
I just put a new battery on it trying to work out the problem.
I've bled air, checked the fuel for water.
The injectors were serviced last year.
Now I start it up and it seems to be running but a release the key and it rolls down to a stop.
Just have no more ideas. Unfortunately I can't find anyone around here to help, professional or otherwise.
West Highlands of Scotland.
Any ideas would be very helpful as I've none left.
Cheers
Justin

[Greg Brannon]

Can you give a little history and more info? Is this a new install? Do you have an engine operator's manual and have you reviewed and followed the start procedures for that engine? Is this a new boat to you? How long since the engine ran correctly? What has happened since? Does the engine have glow plugs and/or a preheat switch? What are you doing with that switch during start? Do you have wiring diagrams for a correct install? Have you checked your installed engine wiring to the manufacturer's diagrams? Is there an electric fuel lift pump that only operates when the key or preheat switch is engaged? When you say 'rolls to a stop,' can you verify that there is fuel ignition while the key is on - is the engine getting warm and exhausting burned fuel or just fuel vapor (cool and damp diesel-smelling white vapor 'smoke')? Add anything else you can think of that might be helpful.

Greg.

[SY Harmony]

Can you turn the crank easily by hand?

[deblen]

You say it "rolls" easily.
Is there a decompressor lever open?
Is there a stuck valve?Remove valve cover & check for valve motion.
Cheers/ Len


https://bukh.dk/upload_dir/docs/FAQ/...%2020%20ME.pdf
https://www.cruisersforum.com/forums...ns-157620.html

[Wotname]

All good questions upthread. Lots of good advice in the CF link posted by deblen.

The DV20 is a pretty basic engine, mostly mechanical (mechanical engine stop, hand starting with decompression levers etc).

Check the basics (valve lash, engine stop lever, decompression levers, clean fuel, bleed etc)

Then check for the 3 necessary conditions for a basic diesel to run - Compression; Fuel; Air.

1.Confirm compression by trying to rotate the engine by hand( with decompression levers normal) - you shouldn't be able to!
2. Confirm fuel by pulling an injector and look for fuel mist while cranking. Ensure the injector tip is pointing AWAY from all body parts and decompress the other cylinder.
3 Confirm air by checking inlet and exhaust passages, mixing elbow etc are clear of obstructions.

If these 3 conditions are OK, then the starter motor is not spinning the engine fast enough during the start cycle. To confirm, crank the engine over (with the starter motor) while decompressed. After about 5 seconds, recompress 1 cylinder
(keeping starter engaged). If it fires, then recompress the other cylinder. If keeps running, then the starter motor rpm is too slow (battery / wiring / etc). If it doesn't fire at all, then it is one of the 3 items above that is the culprit. Go back and check compression/fuel/air.

The most important question is - when did it last operate normally and what has happened since then!

[nuku34]

Hello to the OP,
I've got a Bukh DV20. As suggested above any diesel needs air, fuel, and enough compression to get the fuel hot enough to burn (no spark plugs in a diesel).



1) If you do the injector test as suggested, close the intake through hull first! Cranking an engine without it starting (and with the water pump putting water into the wet exhaust elbow) will eventually fill the water lift muffler and back up sea water into the cylinders causing damage (bent connecting rods, broken crank shaft, etc). Once the engine starts, you can open the sea cock.

2) Bukh's do not have a glow plug system for preheating the cylinders. This makes them a bit hard to start in cold weather. They sometime need to be cranked for a while even after they sound like they have started. If you stop cranking and they sound like they are "chugging" and not running smoothly and then they stop, you haven't cranked them long enough to get the cylinders hot. If this happens and you need to restart, you will need to close the seacock first or risk what I have said in #1 above. Once the engine actually starts, you can open the sea cock and always check that water is coming out the exhaust!
3) Where are putting the throttle lever? You should set it at around 1/3 of its travel, and make sure the engine is NOT in gear.
4) In cold weather you do need adequate battery voltage and reserve amps to spin the engine fast enough to get the cylinders hot enough to sustain fuel burning.

5) If your battery voltage is ok, but the engine not getting up to good cranking speed, it could be a wiring problem (corrosion on the wire connections) or a faulty starter motor.

[JustinT]

Thank you all. So much information to work through!
Last time it worked was last year when I bought it in from the swinging mooring. It did act a bit odd then. Once I tied it up (I moor it on the beach for the winter) the engine started to race and wouldn't shut down. I had to jump the solenoid to the negative. Didn't think much of that really, it's done odd things before, until trying to get it going this spring. Being on land, testing it is tricky. I remove the impeller to try starting or wait for high tide.

I'll work though all the info above and get back to you all. Thank you.

[nuku34]

Hello Justin:
The fact that the engine was racing might suggest a problem with the high pressure fuel pump. There are governors in there that control the speed of the engine.

This unit has to be overhauled by a professional, no DIY! You can remove it yourself and take it to the repair shop, but when refitting it on the engine, there is a very specific procedure for setting the timing using shims. Do not just use the same number of shims again and neglect the procedure. A friend of mine did this and destroyed his engine because he got the timing wrong.

[Wotname]

Originally Posted by nuku34

...................
4) In cold weather you do need adequate battery voltage and reserve amps to spin the engine fast enough to get the cylinders hot enough to sustain fuel burning.

5) If your battery voltage is ok, but the engine not getting up to good cranking speed, it could be a wiring problem (corrosion on the wire connections) or a faulty starter motor.

These two points are worth repeating as they are often overlooked when diagnosing hard to start problems. For the less experienced (like me ), it can be difficult to determine if the starting rpm is just a bit too slow, especially if the start rpm has been decreasing slowly over time.

Even more overlooked is the easy diagnostic tool available engines fitted with decompression levers. As posted upthread, if you are unsure about the starting rpm, crank the engine over decompressed for some seconds and then recompress 1 cylinder. This allows for the starting rpm to build up as there is little load on the starter motor circuit when the engine is decompressed. The now spinning flywheel stores energy and that is delivered back to the engine independent of the electrical energy provided by the starter motor. Put another way - get the flywheel spinning fast enough and let it start the engine!

I swear you can start a small diesel this way with a couple of half flat D cells

[JustinT]

Thanks. I have tried the compression lever (on top) several times, decompressed, then as the starter is going I flick the lever the otherway. I have a Royal Enfield motorbike, so used to compression. Not sure if it is actually achieving anything with the yacht though.

I think what troubles me most is that the engine really seems to be running but once the key is released it just rumbles down to a stop. I wonder if the solenoid is not fully deactivated?

[SY Harmony]

Originally Posted by JustinT

Thanks. I have tried the compression lever....Not sure if it is actually achieving anything with the yacht though.

That makes me think you’ve lost compression.

[JustinT]

Originally Posted by SY Harmony

That makes me think you’ve lost compression.

Is possible I suppose. A yachting friend suggested that might be the case too...

[Wotname]

Originally Posted by JustinT

........
I think what troubles me most is that the engine really seems to be running but once the key is released it just rumbles down to a stop. I wonder if the solenoid is not fully deactivated?

Presumably you are referring to the stop solenoid. If so, then you need not worry too much.

On Buhk DV engines this solenoid is only activated when the stop button is pushed; it is hard to conceive of a fault condition where the solenoid becomes party activated after the start key is released. Of course you can always remove the wiring or even the solenoid to confirm but I won't bother.

Do you have the service manual? If not, it is available here (free). https://bukh.dk/upload_dir/docs/FAQ/...%2020%20ME.pdf

[Wotname]

Originally Posted by JustinT

Thanks. I have tried the compression lever (on top) .......... Not sure if it is actually achieving anything with the yacht though.
..........

Originally Posted by SY Harmony

That makes me think you’ve lost compression.

Originally Posted by JustinT

Is possible I suppose. A yachting friend suggested that might be the case too...

Does your engine still have the raised hand start and hand crank? If so, can you hand crank the engine through compression with the decompression lever in the normal (run) position. If you can, then you have a lack of compression problem (valves / rings / sleeve etc). The hand crank turns the crankshaft at half the hand crank speed thus if the compression is OK, you will not to be able to rotate the engine with the hand crank unless it is decompressed.

If the engine compression is just below the starting threshold, you can get it started by providing hot air at the air inlet - using a heat gun, hair dryer etc.

[JustinT]

Ah, brilliant, thanks for this info, certainly clears up me going down wrong paths. I'll go and run through it on the boat.