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Old 09-11-2015, 20:34   #1
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Question Bukh DV20 valve clearance?

Ahoy mateys...

I am the usually-proud owner of a CO32 with the original Bukh DV20 still running. I suppose that's some grounds for thankfulness right there :-) But the old beast isn't running as well as it used to.

I've been tinkering cautiously with the engine, trying to find out why one cylinder starts far more willingly than the other (which joins in 30 or more seconds later). One thing I checked right away was the valve adjustment.

The Workshop Manual calls for .01 inch for the inlet and .012 for the exhaust. When I checked them, the clearance was about twice that -- .02 at least, all round.

I thought "Aha, smoking gun!" and corrected the clearances; after reassembly, started the engine. It still started hard, with one cylinder leading by half a minute or more. Worse than that, it was now tremendously noisy with major valve clatter. I killed it quick and sat down to think.

The manual is unambiguous. There is no room for misunderstanding. It says .01 inch and .012 inch. And yet my valve clearances were double that. And yet it's noisier with the clearances corrected.

I am not expert in diesel engines. Can anyone tell me whether there is any *reason* why a previous owner or mechanic would have deliberately defied the manual and set such a generous clearance? is there a reason why the correct setting should be noisier than an apparently wrong setting?

To those who say "oh chuck the thing and repower already," believe me I have been considering that option, but it's awfully expensive :-) for the moment, I'm exploring the "keep it running a few more years" option.

thanks in advance for any light you can shed
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Old 09-11-2015, 20:45   #2
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Re: Bukh DV20 valve clearance?

The most logical explanation for excessive noise after adjustment would be that the adjustment was performed at an incorrect crankshaft/cam position.

Maybe run the valves again and carefully confirm position when checking lash.
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Old 09-11-2015, 21:05   #3
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Re: Bukh DV20 valve clearance?

hi... I carefully watched the rocker arm in each case to make sure that it had lifted the maximal distance from the valve. there seemed to be several degrees of flywheel turn during which this maximal distance was steady.

should I perhaps pay more attention to making sure that the flywheel is in the *exact* centre of that range of motion where the gap is at maximum?
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Old 09-11-2015, 21:19   #4
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Re: Bukh DV20 valve clearance?

It could be you adjusted them at the wrong point? Of course that would not explain the slow start on the 1 cylinder, sticky valve, leaking injector maybe?
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Old 09-11-2015, 21:26   #5
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Re: Bukh DV20 valve clearance?

Correct, several degrees appear fully closed.

I suggest watching the intake valve close, then as top dead center approaches look for the timing mark to line up. This will be several more degrees of rotation as the piston is coming up on compression.

Then both intake and exhaust on that cylinder can be adjusted at this time.

Using the mark accurately will help insure it's good to go.

I go through them twice, so I can put that out of mind and move on.
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Old 10-11-2015, 08:43   #6
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Re: Bukh DV20 valve clearance?

Perhaps you have inadvertently altered the setting on the decompression levers and they are fouling the valves when it is running?

See page C21 in the workshop manual.

I have the same engine in my boat - and it fires on one cylinder quite a few seconds before the other. Once it's running it's fine stopping and starting for the rest of the day. I assume the compression is a little more down on one of the cylinders than the other.

It's a lovely engine (35 years old) and so smooth - it's worth persevering with!
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Old 10-11-2015, 09:53   #7
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Re: Bukh DV20 valve clearance?

I'd pull the injectors and have them cleaned and tested, while they are out, I'd use a plastic soda straw to determine TDC on compression to adjust the valves if there is no other way, but I think there may be, beacuse isn't fuel timing usually set at TDC? But assuming a direct injected Diesel the soda straw method works fine, You place the straw in the injector hole and let it rest on the piston, use it to indicate piston position.
It will try to bend and jam so make sure it's free often.

I don't know why but starting initially one one cylinder, then others gradually joining in is pretty common on older Diesels. Have you ever heard a old big Cat Bulldozer with a pony motor start?
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Old 10-11-2015, 10:13   #8
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Re: Bukh DV20 valve clearance?

[QUOTE=a64pilot;1958900] You place the straw in the injector hole and let it rest on the piston, use it to indicate piston position.
It will try to bend and jam so make sure it's free often.

A note on that method for a Perkins type engine. The injector in a Perkins cylinder head does not shoot into the combustion chamber with the piston. It sprays into another chamber above the valve pockets, There is a little metal disk with a small hole in it connecting the two chambers. I am not sure you could use a straw, maybe a piece of bent wire.
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Old 11-11-2015, 02:28   #9
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Re: Bukh DV20 valve clearance?

Unfortunately using a straw or screwdriver will not help finding TDC as the head has precombustion or Lombardo cell fitted. Try changing Injectors around to see if the starting issue changes cylinders, but my thoughts are that one cylinder valve exhaust seat has worn causing the valve to regress out of bounds they are known for it causing DV20 hard starting. When setting valve clearances the motor must be COLD-- inlet 10thou exhaust 12thou.
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Old 11-11-2015, 18:36   #10
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Re: Bukh DV20 valve clearance?

I did say assuming it's a direct injected Diesel, pre-combustion chambers it won't work, cause of course you can't get to the piston.
But surely there are timing marks of some type that you use to determine TDC?


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Old 11-11-2015, 19:21   #11
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Re: Bukh DV20 valve clearance?

Quote:
Originally Posted by a64pilot View Post
I did say assuming it's a direct injected Diesel, pre-combustion chambers it won't work, cause of course you can't get to the piston.
But surely there are timing marks of some type that you use to determine TDC?
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Well I think you could fish a wire down to the piston. There is a passage between the two chambers, obviously.
Timing marks are on some gears inside the engine no doubt.
I think this is a direct injection diesel. There is no difference between the two chambers. On some engines the hole between the two chambers is right below the injector. So it is spraying right at the piston. An indirect injection system would inject above the valve.
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Old 11-11-2015, 22:53   #12
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Re: Bukh DV20 valve clearance?

Sorry, indirect.
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