I have been looking for information on my crank style rotisserie from Northern Tool.  I found one topic here and more recently a video for a rotisserie kind of the same style here:

They talk about if you are really putting your back into cranking the car on it’s side, you should re-adjust for a better center of gravity so it turns easier.  The cranks have shear pins which could break if you are cranking too hard.   I asked a question on this page and will see how they respond to how much weight the crank can hold.

Hopefully someone will find this useful.