You can download a Workshop and Users Manual
Bukh DV10/20 engines are Danish purpose-made marine engines - not industrial conversions. Built like the proverbial "brick latrine". They are well-worth re-building where the spares are available.
Both pistons go up and down together, and there is a balance weight on the crank-shaft.
I had a DV20 in my previous boat, and never had a days problem in the 9 years I had her. The engine was 1984 vintage, and it is still going today (well, summertime). The boat is now used for chartering.
I have a workshop manual, if you require any information, should you not be able to download the manuals.