Bukh DV24 Valve lifter / decompressor

[tonyp]

Since buying our boat 2 years ago, our decompressor lever has never turned the full 90 degrees, so has been inoperative. Removing the rocker cover revealed that its gasket was either over-compressed or an incorrect one had been fitted. (Bukh gaskets are about 3.5mm thick, this was about 1mm. ) The result was that the rocker cover was too close to the cylinder head, leading to the decompressor lever, which is fitted in the rocker cover, mis-aligning with the decompressor shaft. The alignment must be correct to within 0.5mm, I'd guess.  
I tried fitting a new, thicker gasket, which was fine till I tried to torque the rocker cover nuts down to the correct value, but once again the lever and shaft mis-aligned.  This time it was probably because the gasket material was too soft. So I then bought a Bukh gasket, (at great cost), on the assumption that it would be of the correct material. But found that it wouldn't work either! In that case I think it was because the gasket I was sent was badly mis-shapen, and was squeezed out of position. (I should have sent it back but was in too much of a hurry).  Getting the rocker cover back on again without moving the gasket is difficult because you have to try to fit the cover against the pressure of the compressor-lever spring that tries to twist the cover off centre. So you have to have the right gasket, in exactly the right position and don't dislodge it even a fraction on reassembly.  

I have spoken to Bukh UK, and to a local Bukh engineer, neither of whom was aware of this "sensitivity" to alignment, or had come across this problem before.

Am I missing something here? I am trying to find a thicker, and more "incompressible" cork/nitrile material to make another gasket before having another go, but anyone any ideas?

Tony

[Sula]

I would be interested to know the answer, as my DV36 decompressor doesn't appear to work (but has not yet got near enough to the top of the to-do list for detailed investigation). 

I doubt that the rocker gasket/cover fitting is that critical, having rummaged around on the internet and found numerous references to refitting the Bukh rocker cover, but no cautions or complaints about problems.

I have heard of someone having problems with a rebuilt Bukh not starting properly and it turned out to be simply the decompressor was not set properly and was holding the valve slightly open all the time, so maybe your decompressor is out of adjustment the other way?.

The following links to an explanation of how the decompressor is adjusted: www.ybw.com/forums/showthread.php?223348-Bukh-DV-20-Decompression-lever-adjustment  


 

[tonyp]

Since writing the original post, and after discussion with my marine engineer brother, I am now beginning to think that the decompression shaft has been removed at some time and, when replaced, the return spring has been incorrectly located. The exploded diagrams in the workshop manual seem to show the spring's fixed end as being lodged against the cylinder head rather than against the inside of the rocker cover. This makes sense. When I get back to the boat next week I can check this. If so, then correcting the spring's position will make refitting the rocker cover perfectly straight forward.
It still leaves the mis-alignment of the shaft and lever, but maybe something else was incorrectly refitted at the same time!
Does your decompression lever turn through 90 degrees, Sula? Mine wouldn't. It started to bind after about 45 degrees, and moving it any further seemed to require such pressure on the lever that there was a risk of breaking something. If yours turns the full 90 degrees it could just be that adjustment is required, which, as you say, is fairly simple, but means taking off the rocker cover.

Incidentally, the valve lifter arrangement for the DV10 and 20 is different from the 24,36 and 40 engines, so the problems and comments above won't apply to the smaller engines.


Tony

[Sula]

I hadn't appreciated the DV24 shared the decompressor arrangement with the DV36, rather than the DV20.

Here's the relevant extract from the current Workshop Manual for the DV36, in case it's of help:

    Adjustment of valve lifter arrangement

Furthermore, a common shaft for decompression is fitted on the three [presumably 2 on the DV24] rocker arm columns.

For a possible removal of the shaft, remove first the pins going down on the rocker arms at decompression, after which the shaft can be pulled out.

When adjusting, adjust the pins so that you faintly see a single groove of the pin thread (about 1.5mm free pin) just on the side facing the rocker arms.

When fitting the top cover, ensure that the slot in the decompression handle in the top cover mesh with the corresponding pin on the decompression shaft.


I'll check the extent of rotation of the decompressor handle next time I'm on the boat.  

[tonyp]

Here attached (I hope) pic of DV24 with rocker cover removed. The valve lifter shaft runs across the bottom and the lever on the rocker cover slots around the tongue at the right hand end of the shaft. The shaft is in the engine's normal running position. The adjustment pins are either side of the return spring, seen in the middle of the shaft. To adjust the pins, you put an allen (hex) key into the end of the pin, back off the lock nut, adjust and relock.
The return spring seems to be fixed in the only place it could be and its free end (pointing downwards) can only lock against the side of the rocker cover once it is refitted. It's too short to reach down to the cylinder head. So this must be normal, but doesn't accord with my exploded diagram. 
To avoid the gasket moving and possibly leaking when you replace the rocker cover you have to lower it carefully, and as centrally as possible over the locating studs ( those that hold the rocker shaft, ) as the spring pressure comes on and tries to push the cover out of alignment. I fitted another (!) new gasket, this time a 5 mm high density cork nitrile one and fitted it dry. Everything went together OK and the decompressor seems to work, but it will only be once the engine has run for a while that I'll know that it works properly.  Even this gasket moved a bit and the next time I do this I plan to use Hylomar blue to stick the gasket down to the cylinder head, let it dry, then replace the cover. Hylomar doesn't set solid, but it'll hold the gasket long enough to resist minor movement.

Tonyp

[Sula]

Tony, some thoughts/ramblings that may or may not help.

Your valve lifter shaft looks different to that in the Parts List exploded view for the DV24, as well as the spring being in a different position as you mentioned.

In the Parts List the spring is shown at the far aft end (left hand end in your photo) of the shaft, not in the middle. That could be just to show it separate to the shaft for visibility, but I notice it is also shown the other way around to yours: the 'leg' end is shown both aft and facing in towards the rockers, and the 'eye' end is forward. That your spring is on the shaft just where there is least room - where the 'waist' in the rocker joint/gasket comes inward - could be part of the problem.  Is there perhaps something at the aft end of the rocker cover that the spring locates against?

The exploded view diagram also shows at the aft end of the shaft a set screw, and in between that end of the shaft and the rearmost pin which operates on the rocker, a 'headless screw' and 'nut, DIN 934'.

The exploded view shows nothing on the shaft between the two operating pins, which is where you have the bolt to which you have fixed your spring. (Curiously, on the DV36 the headless screw is located between the rearmost and centre rockers, in a similar position to your bolt holding the spring, but it is shown projecting from the opposite, outward side.)

I suspect there is something amiss in either your shaft (wrong one, or on back to front?) or the way the assembly is put together, and is resulting in your spring being in the wrong position and causing the problems you have getting the rocker cover and gasket on (which I have never seen mentioned elsewhere), but never having seen under the rocker cover of one of these in the flesh, I can't work out what that could be.  

I am stumbling in the dark because I don't understand

(a) what the 'headless screw' is meant to do (control how far the shaft turns back under the spring - i.e.it's normal resting position, perhaps?), but without a head it wouldn't hold a spring as per your arrangement;

(b) what the set screw does (neither the DV36 or DV48 has one); or

(c) what holds the valve lifter shaft in position lengthways.

The above things may well be connected!

Good luck with it.  Let us know your progress.

John

[tonyp]

Some news, John.
I sent the photo I'd posted here, on to Bukh UK, and got a very useful reply from their engineering manager.  As we suspected the return spring should stop against the head and not the cover. As mine certainly couldn't reach the head, I now wonder if the "tail" has snapped off. 
The Bukh gasket used to have adhesive on one side to stick it down when replacing the cover, but not sure why the one I recently received had none.  That would have the same effect as using Hylomar, as previously posted and ease accurate placement.
Finally, I'd been given duff gen by someone at Bukh about the torque for the cover nuts! They just screw the cover nuts down hand tight, then, roughly, add another half a turn. They recheck for oil tightness after period of running and tweak up as necessary.
Bukh don't have a DV 24 in stock to send me a picture of how the return spring should be fitted, so I will have to buy a new one and work it out myself!
Hey ho!
Tony

[Sula]

Glad to hear progress is being made.

[tonyp]

I have learnt, to my horror, that Bukh won't supply a replacement return spring. Instead they insist I buy a complete new rocker and valve lifter assembly for £310.76 plus VAT plus shipping. 
I'll continue with the non-standard system, which now works, and meantime look for a spring supplier. 
Anyone want a 2005 Bukh DV24?
Tonyp

[Sula]

Jun 15, 2018 9:21:09 GMT tonyp said:

I have learnt, to my horror, that Bukh won't supply a replacement return spring. Instead they insist I buy a complete new rocker and valve lifter assembly for £310.76 plus VAT plus shipping. 
I'll continue with the non-standard system, which now works, and meantime look for a spring supplier. 
Anyone want a 2005 Bukh DV24?
Tony

Yikes!   Seems a surprisingly reasonable price for such an assembly, but an outrage for a spring.

If you can't track down a replacement, there are people who can make springs one-off.  


Or perhaps, if you were able to establish the tail was definitely broken, and how long it needed to be, you could have a bit welded/brazed(?) onto it, or epoxy on a suitably sized bit of narrow tubing? 

[Sula]

Tony,

I've asked for advice on the YBW PBO forum, but didn't get any suggestions you haven't thought of yourself, apart from perhaps trying Marine Enterprises, who may have second-hand spares. (I believe they sell 'refurbished' ex-lifeboat Bukhs.)

It is unusual to not to get lots of experienced based advice (along with wild guesses!) on there, and that coupled with the lack of any photos on Google showing a DV24/36/48 with the rocker cover off seems to suggest they are amazingly trouble free in that area.

I did find the following German site selling the spring alone for €45.82 + shipping www.hafner-bootszubehoer.de/product_info.php/info/p177405_bukh-feder-bb-000e4902.html

That said, I'm not convinced your spring is broken. Looking at your photo enlarged it appears that the end of the 'leg' of the spring is slightly bent over, in accordance with the drawing in the parts list. If the leg we're broken off short it wouldn't have that bend.

If the spring is OK it gets back to the question of where/how the spring should fit. I'm convinced your spring is fitted the wrong way round (from looking at the drawing in the Parts List), and suspect that it should be in a different position on the shaft (probably at/near the aft end).

Unfortunately, I didn't get to my boat yet again this weekend, so I was unable to check the decompressor lever travel for you.

[tonyp]

I've made another couple of gaskets, (!) so when I get back to the boat next week I'll take the rocker cover off again and check the spring length again, John. I'll either find that I mis-measured it and it can actually be made to reach the head, or I'll get the correct measurements for making a eplacement. Thanks for the details of the German supplier. I've also found a couple of UK firms that will make a spring. They seem likely to charge less than the German one. 

Re the Bukh exploded diagram, I'm beginning to think it's wrong! The winding they show on the torsion spring, if it were fixed onto the shaft the way they show it, would keep the valve lifter forced against the rocker in its normal state, rather than off the rocker, which should be its normal position. It also couldn't fit onto my shaft with its leg to the aft end of the engine, as they show it. The hole for its fixing bolt would then be covered by the spring. Maybe this is part of a Bukh plot to ensure that only their own fitters work on their engines!

Tonyp

[Sula]

Tony, Have a look at the cross section drawing on page C8 of the DV24 workshop manual here - bukh.dk/upload_dir/docs/FAQ/Bukh%20RME%20%20-%20Data/Bukh%20RME%20-%20Workshop%20manual/Work%20Shop%20Manual%20DV%2024.pdf

You can see the tail of the spring coming down from behind something, and its curved end bearing against the inside of the rocker cover. So now it appears you do have have the spring the right way around, and that it's not broken.

Next, you need to confirm its correct position lengthways along the shaft. Look carefully for corresponding wear or stain marks at the relevant height on the inside of the rocker cover. Is there one corresponding to the current position of the spring? Are there any others (i.e. could it have been reassembled wrongly at some point to end up where it is now)?

Hopefully that will make Bob your uncle.

[tonyp]

You're dead right, John! The spring does fit against the rocker cover, and on mine it can't go anywhere else on the shaft because the spring is bolted to the shaft through the only possible hole. So the original fault was the incorrect/over-compressed gasket. As long as the homemade gasket I've put on doesn't leak, I'm now going to leave well alone.
Thanks very much.
The lesson here might be to take Bukh advice and drawings with caution. But I'd recommend anyone replacing the rocker cover gasket to stick it down to the head with Hylomar before replacing the cover. It can save a lot of swearing and angst.
Tony

[Sula]

Glad you have it sorted. I take it the lever is operating properly now?

What did you make your gaskets from?