I never got involved these engines in any depth, due to not been impressed with several of the cheapening up features on this engine range.
Anyway back to your problem, if these engines are anything like the earlier LP engines I have worked on. You will have noticed the main bearings are located in circular housings (cheeses). These cheeses are located in the crankcase with hollow dowel pins (which are not obvious unless you know where to look). There may also be other dowel pins which are located under bolts in other areas of the crankcase.
Proceed to remove any likely bolts that appear to have no immediate function, and the oil pipework from the main bearing area, and if you probe down these holes [with a suitable O ring pick or similar], you have now exposed in the main bearing area of the crankcase casting, you will feel a hollow dowl pin, these are threaded so you can extract them with a suitable size of studding.
Once removed you can extract the crankshaft complete with the main bearing housings from the crankcase.