Diesel (Bukh) starting oddity

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jerryat

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Hi all,

A few posts but only my second thread.

Any ideas what's causing this problem on a 2-cylinder 20hp Bukh diesel engine that, after a major refit the season before last, ran beautifully all last season. The refit included new liners, pistons, rings, pump etc etc.

This year, after launch, the engine requires about 8 - 12 seconds to start (as opposed to the usual 4-5 seconds) during which period it fires on one cylinder a few seconds before the other one, but then runs like a sewing machine, just as it did all of last season. I have deliberately motored for 6 1/2 hours, including half hour periods at full throttle, to see if a good blast would 'clear' things but, while it never missed a beat, and ticks over beautifully, the odd starting continues.

This applies to the first start of the day and subsequent starts during that day are very quick, though you can still detect the second cylinder coming 'on-stream' about 3 seconds after the first.

The changes made during the winter were:

1. Cylinder head removed and new valve springs fitted (should've done it during the refit but forgot!)
2. Both injectors removed and serviced by Lucas (both fine)
3. Startron enzyme fuel treatment added to tank. The fuel filters were changed (in case of any resultant contamination after 10 hours) but were fine.
4. HIgh pressure fuel pump serviced and parts renewed by Lucas (now perfect)

I appreciate that many diesels take a while to start and, if mine had been similar, I wouldn't have been concerned, but we are hoping to push off long term cruising again shortly and I want to find out why the change!!

Sorry it's a long post, but I think all the info's there.

Any ideas would be much appreciated 'cos I'm stumped!!!.
 
Dont know this engine but I would first find out which cylinder is not starting, (touch the exhaust near the head on both) that will soon tell you ! then swop the injectors over, see if problem follows the injector, if not, suspect valve clearance ?
 
Hi essexboy,

It's difficult to spot which cylinder it is (I've tried!) because we're only talking seconds before the engine's running normally. Tried disconnecting the fuel lines in turn (i.e. one on one morning and the other the next) but as I say, damned difficult to be definite that 'that's the one' in such a short time.

Definitely not valve clearances as I've checked these a couple of times, more in hope than belief they were wrong. A fault here would produce a constant problem, and the engine is otherwise perfect.

Thanks for the ideas though!
 
Hi Jerryat, as with essexboy I don't know this engine but would ask....

Does it have glow plugs and if yes are they both working correctly ?
 
Bukh uses an optional manifold heater for cold start. Not often needed in this country - more for cold Scandinavian winters!

I would suspect a slight compression leak on one cylinder after replacing the cylinder head. Did you thoroughly clean out the groove in the head which helps the gasket seat properly round each cylinder? A slight leak would make cold starting more difficult on the affected cylinder, but would otherwise run apparently perfectly.
 
Hi MEP and oldharry,

MEP, yes, there is a glow coil (cold start) facility on the engine, but we never need to use this, so I am comparing 'like with like' in not using it now. From curiosity, I did try a couple of times, but though the starting sequence was a bit quicker, the basic situation (one cylinder firing slightly before the other) remained.

oldharry, yep, I am very fastidious about cleanliness etc when working on the engine and made absolutely sure both the block and cylinder head were spotless. The compression has been properly checked and is 'as new', which I expected with new liners, pistons etc.

As mentioned, the engine runs superbly once this intial start is over, and starts almost immediately thereafter (during the same day) but still with a tiny 'lag' between the two cylinders firing up.

Baffles me as well as Lucas and Bukh Diesel UK!!!

Many thanks both for your ideas.
 
I experienced a similiar problem with my DV24 and it also baffled Bukh. On their advice I checked the tickover RPM and found it had dropped off a little so reset it back up to 900rpm (although the range is 900~1200rpm) and she is back to "normal".

Any chance you upset the tickover speed during the rework?

Apart from that I have no idea of why the sluggish start and "rough running initially" although I believe the DV20 and 24s all run a little rough immediately after starting until the injection timing stabilises.
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"Artificial intelligence is no match for natural stupidity"
 
Hi Cliff, Thanks for that.

The tickover is 1050rpm which is fine for my engine. There isn't rough running at any stage, but just this sluggish starting, primarily on one cylinder.

I'm going to 'play' with the engine again tomorrow to see if any other suggestions leap out at me, and may even whip the head off and double check that if all else fails.

The engine is over 22 years old and has done a lot of service (we've done 45K miles in the boat) hence the major engine update the season before last. Accordingly, we won't spend a great deal more time/money on it, as we want to get away cruising in a few weeks time, so a new engine may be the last resort.

Not quite as daft as it sounds as we hope to be away at least three years and will cover many thousands of miles. We want to have total confidence in the motor (which we've always have until now) and not have to keep wondering if things are gradually going wrong.

Not gonna give in without a fight though!!

Thanks again,

Jerry
 
Another thought which is probably off base but... any chance of air getting into one of th einjector lines through a dodgey union/ This would prevent the injector "breaking" properly until any air bubble was bled off (a few turns od the engine could be enough to force the air bubble through the injector).

I had problems a while back with my diesel generator - real pig to start but once started would restart all day lon - leave it over noght and same problem. The problem was eventually traced to a damaged copper washer on the union at the injector. Replaced the washer and problem solved.

As I said "just a thought"
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"Artificial intelligence is no match for natural stupidity"
 
injection timing doesnt "stabilise" it is fixed by a mechanical "connection" and once set is either right or wrong. suspect a small air leak in one of the cylinder fuel line connections.
stu
 
I suggest you go talk to Bukh uUK before you make such erroneous statements and futher show your lack of knowledge of the subject matter. The timeing in the Bukhs is certainly NOT fixed.
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"Artificial intelligence is no match for natural stupidity"
 
Hi Cliff,

Yep, one of the first things I checked was unions/connections and even had the fuel lines themselves tested just in case there was a microscopic hole somewhere!

After further discussions with Al Pearson at Bukh (who like me, was certain it was a fuel problem) I'm going to take the head off in the next few days to make sure that the head gasket hasn't been damaged or there isn't a valve sticking.

I did check the latter though by removing the rocker box and they appeared fine.

Frankly, if I was just messing around in Brittany or along the south coast this season, I'd live with the initial slow starting, but because of the proposed long trip, SWMBO is rather keen on replacing the 22 year old unit with a new one, just for the added reliability and peace of mind.

I think you have the latest 24hp direct injection engine don't you, so are you pleased with it? Al Pearson reckons the starting is fantastic even in below zero temps.

Cheers Jerry
 
we are talking about a misfire on one cylinder, if the auto advance and retard is sticky then it would affect both cylinders.
yawn yawn!!
 
[ QUOTE ]
..... but because of the proposed long trip, SWMBO is rather keen on replacing the 22 year old unit with a new one, just for the added reliability and peace of mind.

[/ QUOTE ]I trust you are thinking of another Bukh rather than a "marinised tractor engine" /forums/images/graemlins/grin.gif[ QUOTE ]
I think you have the latest 24hp direct injection engine don't you, so are you pleased with it? Al Pearson reckons the starting is fantastic even in below zero temps.

[/ QUOTE ]Yep, one of the latest 20 year old ones! Apart from a few adjustments and the odd easily rectified starting problem (sluggishness and initial rough running) she has been, and still is, great. I do not have glow plugs or any form of preheat and even in the middle of winter she has been starting within a few turns, even if left for a few weeks. One of the other things I do like about the Bukh is the backup from Al or Normal at Bukh U.K. - They are always willing to talk you through a problem and I have found their advice spot on on every occasion.

I had a similar problem to you with sluggish starting and real rough running for a few seconds after she fired - sounded like it could have been firing on one cylinder only - but turned out to have been the tick over speed had dropped a tad too much (#1 son was cleaning the engine and changing the sacrificial anode and as it turned out had moved the tick over adjustment to fit the new anode and carrier - he did not realise it needed reset accurately /forums/images/graemlins/laugh.gif).

The DV20 and 24 are basically the same engine except the 24 is direct injection (at least according to Bukh and the manual).

You don't know anyone nearby you that has the same engine and would let you borrow their injectors? - just to eliminate yours as a source of the problem.

Do let us know when you find the problem - I am sure it is nothing serious.
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"Artificial intelligence is no match for natural stupidity"
 
While not doubting Jerry's view that she is firing on one cylinder initially, these engines do run rough for a few seconds after starting and can on occassions sound as if they are misfiring on one cylinder. It would appear from your posts that you do not have, nor ever had, a boat with one of these engines.
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"Artificial intelligence is no match for natural stupidity"
 
Its irrelevant whether I own or have owned a boat with one of these engines, I am a retired maintenance man with years of experience of teaching foreign nationals how to repair a whole raft of diesel engines ranging from two stroke diesels through to massive gas fired diesels. The size and method of getting the fuel into the cylinders is as diverse as the world is large however the principle is exactly the same and if one applies basic principles of trouble shooting the answer is always arrived at. Scatter gun trouble shooting is not the way I was taught to work and I made sure that my trainees did not do this either. Off the cuff remarks do not help people on the forum and indeed can lead to the formation of "urban myths" which only serve to confuse people.
 
[ QUOTE ]
Off the cuff remarks do not help people on the forum and indeed can lead to the formation of "urban myths" which only serve to confuse people.

[/ QUOTE ]Glad you realise that. Please stop making them.
EOD
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"Artificial intelligence is no match for natural stupidity"
 
I ignored this topic at first because I have no specific knowledge of Bukh diesels but I have now read it and it reminds me of a discussion about similar starting problems that was on here sometime ago. I forget all the finer details but I do remember that the problem disappeared, I won't say was cured, when the original questioner painted every thing. I don't know why he painted it, he just liked it all to look pretty I guess. The general conclusion was that there had been some small leaks or just one small leak on the fuel system which were/was so small that no fuel leakage was apparent when the engine was running but were/was large enough to allow some air to enter slowly when not running, the fuel draining back to the tank. This meant that one cylinder did not fire until all the air was purged. Once some paint at been applied it stopped the air ingress, maybe only temporarily.
I can't say I was totally convinced but once joints have been disturbed leakage is always possible. Washers, and olives harden and although flat washers can be replaced (Eg on banjos) it is not possible to renew olives without renewing the pipes. Further tightening of compression joints is not always successful and can eventually make matters worse.

In the current case all the joints have been broken and remade several times it seems so if the explanation of the previous case was correct then it could explain the current problems also. How you would find the leaking joint(s) though I have no idea but I would have thought that a small fuel leakage might be detectable during prolonged running. Or I suppose You could paint the joints and see if it made any difference.

Just another idea thrown into the ring since it seems general opinion is in favour of a fuel system problem. I would start removing a cylinder head only as a last resort.
 
Re: Cliff and Stu

You both make valuable contributions to these forums but public slanging matches do nothing to enhance your credibilty, and frighten away those of us of a sensitive nature. If you must squabble do it in private by PM please or just state your opinion on the facts and shut up.
 
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