A friend has a '71 Cutlass with a 455. Runs fine, doesn't overheat, but the full-size starter heat soaks and prevents proper starting when hot. They have tried an insulated wrap but to no avail. Anyone have a good solution for it?
Thx guys.

 

Check both of the battery cables. The braided cables can have strands break and become frayed at the ends and then there are not as many conductors carrying juice to the starter. Learned this one the hard way.

 

The problem is excessive resistance in the START circuit, resulting in low voltage at the solenoid. be sure the connections in the entire START circuit are clean - that includes the NSS as well as the ignition switch, and also the terminals in the firewall connector. Also, when was the last time the starter was rebuilt? The contact disk in the solenoid and the mating terminals in the cap get pitted, which increases resistance and lowers voltage in the coil. Finally, do you have the starter strap in place? The strap isn't just a support, it also provides a ground path from the starter to the block. If that strap is left off, the ground path is from the steel starter case to the aluminum nose to the iron block. Galvanic corrosion increases resistance there. The strap is steel and minimizes galvanic corrosion. Each of these is a small voltage reduction, but taken together they can prevent starting.

 

I strongly prefer a metal heat-shield vs. an "insulating wrap".

The "wraps" are as good at keeping heat IN the starter, as they are at keeping exhaust heat AWAY from the starter. At least the metal heat shields permit the starter to cool after long crank cycles.

Joe P talks about the "START" circuit, which comes down to the purple wire connected to the "S" terminal of the solenoid. Test voltage drop there when the starter is cranking. You should have almost battery voltage at the "S" terminal, keeping in mind that the battery voltage will be reduced due to the load of the starter--about 200 amperes is typical, some Olds go a little higher than that.

Another issue can be worn brushes, worn bushings, and partially-shorted armature or field coils. Usually, it's the voltage to the "S" terminal. A work-around is to use the existing purple wire that was on the "S" terminal to trigger a relay, or a "Ford Solenoid" on the fender. There's more than one way to wire those up.

 

A few weeks ago, I replaced the starter on the lady's car of which I swapped mine with hers. It would start up just fine, when cold. But, would act up warm. It turned out to be the solenoid.
The larger the starter, the more time it'll take to cool it down for driving away from inconvenient locations. Therefore, aren't gear reduction starters yet available for classic GMs? The motors in those are much smaller. Therefore, they won't absorb so much heat. You can still be a purist, while using a modern starter, as long as you keep the old one stashed somewhere