Hi,
Below is the Cub and LoBoy service manual, it has lots of info.
I would read the engine section, section 1, before working on the engine.
There is a contents beginning on page 1 of most sections, that makes it easier to use online.
http://farmallcub.com/rudi_cub/www.clea ... index.html
You didn't say the year of the Cub. This manual was made in the 1970's so it has newer, 12 volt electrical system info.
I don't know what you meant by drive shaft. The crankshaft goes in the lower part of the engine.
You didn't say if the crankshaft you are using is in good condition, the bearing surfaces should be measured with precision tools, that an engine repair shop probably has, to check it for wear.
The bearing surfaces should be smooth.
Each of its bearings has to be fitted right, and their clearances checked using Plastigauge.
It explains how to use Plastigauge in the manual. It is sold at auto parts stores, like NAPA. It is like a small string.
The clearances all have to be .002" to .003"
The crankshaft info begins on page 1-47, info about Plastigauge is on page 1-50.
If the crankshaft journals, they are called, are worn too much, or out of round, it needs regrinding at an engine shop. Then it would use undersize bearings.
Below is a pic from TM Tractor Parts of crankshaft journals, they are in good condition, new ones look better.
Remove any paint from the engine where the front end, and clutch housing bolt to it, so the electrical system can ground through the tractor.
Remove the paint where the generator bracket goes, so that can ground.
