Car will not start when hot

Rework the grounds on the starter brushes
Clean up the matting surfaces of the starter
Clean up the matting surface of the starter to block - ie remove all the pretty shiny thick paint.
Then make sure you have good ground of the starter to the frame
And then also add in a ground from the engine block to the frame.
And, I love my Optima battery, though they are difficult to charge when they get a low charge.

Rework the grounds on the starter brushes
Clean up the mating surfaces of the starter
Clean up the mating surface of the starter to block - ie remove all the pretty shiny thick paint.
Then make sure you have good ground of the starter to the frame
And then also add in a ground from the engine block to the frame.
And, I love my Optima battery, though they are difficult to charge when they get a low charge.

Mike,
You were talking about putting in a new radiator with a modern core, did you? I would have thought that would have solved your problem.
Frank

I agree with Curt: I had the same problem and it was fixed when the brushes were properly grounded. Engine cranks nicely, even after it is hot.

Hello Michael,
From my experiance rebuilt car and motorcycle engines turn over easier when they are hot due to the oil being less viscous and the components at their correct operating clearances . I suggest you turn the engine over with the hand crank with the engine cold then hot and compare the difference, you may need to remove the plugs. This will help eleminate any possible starter motor problem that may be accuring when the starter motor is hot. If your engine is that tight you will not be able to turn it over with the hand crank even with the plugs removed. If it is the engine then possibly a component has not been given the correct clearance.

Freshly rebuilt engines are tight, and this brought out an underlying problem.
I suspect that you have a grounding problem.
The cables should be at size 00 or better. Do the early cars have lead washers between the cable and the frame? On 34-36 cars there is an additional ground strap from the starter to the frame. Is the starter motor to the bell housing clean. Lastly and very important, the grounding brushes need to be grounded directly to the starter motor frame. Not through the rivet in the end plate. Typical re builders replace the bearings, brushes and install a new bendix. The grounding brushes will ohlm out just fine untill there is 600+ amps trying to find their way home.

My experience is with 34-36 Auto-Lite starters not the early Delco's, but the principal is the same. 9 out of 10 electrical problems with old cars is poor grounding.

Sounds like it was rebuilt too tight on some area like bore to ring diameter. The rings create the most drag in any engine. How many miles are on the rebuild? I would run the engine and get at least 1000 miles on it and see if it loosens up. What breaks in the ring to bore is to run up the rpm and then let off the throttle. What your doing is wearing the rings on both the top and bottom side as they go up and down in the cylinder. If you can find a long straight road or large parking lot do this till you feel its driving you crazy. Then drive home and see if the engine frees up. Not actually seeing the engine build I can't say for sure how it was put together and how tight it is.

My 1931 Auburn 898-A recently had a rebuilt engine installed. The car operates on a 6 volt system. The starter was rebuilt also. The problem I am having is that the car will turn over, with much effort, and start when the engine is cold. After driving the car it simply will not turn over until the engine has cooled. My mechanic said that after the car has been driven for a time it will loosen up and the starting problem will be solved. I am hoping he is right but not convinced. I have 2 6 volt batteries in parallel but to no avail. Any suggestions /ideas will be appreciated. I have a modern radiator which works fine and the engine does not overheat--it runs at a consistent 170 degrees.