Bukh DV8 will not crank

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blackfish

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My boat has been out of the water since last autumn, and because of COVID I haven't been near her since then until today.

She has a very ancient Bukh DV8 single cylinder inboard. Under normal conditions it is possible to get the flywheel to turn about a quarter of a revolution by hand, before compression builds up and the rotation stops. Today I can get nothing to move at all. I tried some leverage with a big spanner on the flywheel nut, but to no avail.

Last summer I replaced the exhaust manifold elbow with a new casting (non-standard). I'm wondering whether some water has got into the cylinder and the pressure preventing turning over is hydraulic.

Any suggestions for investigating further gratefully received.
 
Last edited:
Remove glow plug if it has one, if not then injector. Also check oil for water contamination. A squirt of oil in the cylinder might help in case the rings have rusted to the bore.
 
A hydro lock would allow you to move it away from compression; if you can't shift it at all it's likely seized. Make sure it's out of gear and the shaft free to turn, as above to relieve compression(although on a Bukh the decompression lever should be enough) should allow turning if not seized. Once seizure is confirmed it's off with the head.
 
Steps as above. But you could try a pry bar on the ring gear having taken the starter off can help exert more pressure.

A cocktail or diesel and motor oil down the injector port should free things off. Hopefully just damp atmosphere and lack of use that’s lead to it. If you find fluid in the bore then you’ll need to identify the source!
 
I've found (shamefully twice) that patience is really a virtue here as once the 'release fluid', just diesel in my case, is in the cylinder, it did need time to work before it began to move with a bit of force, then easing quite swiftly. If you're lucky with just a small amount of effort it'll all free up quite easily. If not, it's a head off job, piston ring replacement and so on.
Both times it's worked out OK with a bit of work, and new rings both times, simple enough in the end.
 
Sit Rep:

Injector removed (it took nearly two hours. Clearly hasn't been out for some time.) A cocktail of lubricants inserted. Still wouldn't budge after half, then a whole hour. Left it to stew for a few days to see if anything shifts.
 
blackfish said:
Sit Rep:

Injector removed (it took nearly two hours. Clearly hasn't been out for some time.) A cocktail of lubricants inserted. Still wouldn't budge after half, then a whole hour. Left it to stew for a few days to see if anything shifts.
Click to expand...


Did you use diesel or a mixture of oil and diesel as suggested earlier. It takes less time than just oil.

Just get the diesel out before running.
 
After a week of "soaking" and some more lubricant today, nothing. It will not budge at all. So I thought I would try to take the cylinder head off. I cannot get any of the head bolts to budge either. After two hours (and some scraped knuckles) I have retired hurt.
 
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