Classic/Antique Car Repair: starting problem, good luck jack, battery cables

Question
Hi Jack;
I have a 1931 roadster that starts cold & will  roll  over  with
no  trouble  at  all, but  when  the  engine  is  warm  the  starter can  not  roll  the  engine  over  to  start, I  have  to
boost  it  with  a  power  pack  of  12  volt, it  only  takes  one  turn  of  the  engine  to  start,  other  than  this problem  the  engine  runs  great. thanks

Answer
Well that is a tough one. If you have float-a-motor engine mounts, be sure you have a grounding strap between the engine or trans to the frame.  Make sure you are using 6 volt battery cables. The 12 volt cables don't have enough copper in them to carry the current. When hot, the voltage drop is too great.  The last thing I can think of is the starter motor.  Borrow one from someone in your club and try it. I hope you are in a local A club.  Let me know what you find. It has me stumped.  I'll keep trying to think of other possible causes. Good luck. Jack

Robert, make sure you have a good battery. One cell may be weak or shorted when hot. Jack

Another thought. Make sure all battery connections are tight. Also check the crimp between the battery cables and their end fittings.  They sometimes become loose and can fool you.
Jack