Allis Chalmers 5020 problem

[Traditional Farmer]

Bought a 5020 'Pig in a Poke' won't start its getting fuel,valves look to be working correctly,
etc but its hard to turn over and won't crank very fast as if the timing is off but nothing been messed with in that area I don't think and the starter seems OK.Have good battery and jump box and even pulled in high gear and the wheels slide.Anyone know these tractros to hazard a guess what it is before I dig deeper like pulling the head?
 

[Dick L]

Heaters in the head. They must be working or starting is almost impossible. They may not be bad but lost connection. Clean the connections and see if that helps.
 

[180doug]

Put ur hand on the starter ,if it gets hot get it rebuilt , the engine has to spin fast to start
 

[Dick1955]

bad connectors usually slow them buggers down
 

[Dick L]

Added to what Dick1995 said would be to check the cable size as well. Mine has a cable larger than most (auto) 12 volt cables. I have never sized it but it looks to be as large as the old 6 volt cables. Along with loose connections a light battery cable will also slow down the starter.