Top dead centre Bukh DV 20

[richardc]

I have an LM 27 with a Bukh DV20 engine and need to adjust the valve clearances but in order to do so I must find “top dead centre”. My flywheel doesn’t have any markings to guide me, is there an easy way to find this ? I do the annual service and have enjoyed getting to know this engine, so I am keen to do this as well, especially as the manual recommends this adjustment is carried out regularly. I could take the easy way out and get a professional to do it for me but that way I wouldn’t learn anything and couldn’t call myself a practical boat owner ! Your advice would be gratefully received.
Richard Carvell

[Sula]

I've not done the valve clearances on that particular engine myself, but the Workshop Manual says only that it has to be 'near top dead centre on the compression stroke'. That should be easy enough to find if you have a starting handle (requires a bit more ingenuity and an appropriate spanner if you don't), just turn engine gently until it stops on compression. Though not explicitly mentioned in the manual, I guess it means compression stroke of the cylinder you are adjusting the valves on. All that really matters, as far as I can see, is that both valves are fully closed when you adjust them.

The Workshop Manual can be found on the internet, if you don't already have one.

Key points from it:

Adjust when engine fully cold;
Check head bolts torque first, tighten all bolts, evenly, in cross-wise order, so that each is tightened alike - DV10 15-17kgm / 108.5-123ft.lb - DV20 9.5-10.5kgm / 68.7-75.9ft.lb;
Adjust when near TDC on compression stroke;
Clearances - DV10 0.25mm / 0.01" - DV20 0.30mm / 0.012"

Hope that helps.

[richardc]

Many thanks for the reply , I will give that a go tomorrow morning, I do have a starting handle so should be easy enough to find it that way. Sounds more straight forward than I imagined.
Regards Richard

[chrismunson]

When you hand crank the engine, be sure the fuel is cut off. It could start even on half a revolution. Could be quite a surprise.

[Deleted]

Turn flywheel in run direction. When exhaust valve is closing and inlet valve open at same moment you are at BDC, so now turn flywheel 180 degrees forward and that is TDC. Now adjust valve clearance. There is no danger of starting engine by hand turning so close off fuel is not necessery.

[Richard]

Thanks to all for this advice, not had a chance to try yet but will do over the weekend.