Looks like it's a heat related thing. Either something in the engine\clutch area is overheating and expanding to the point of locking up the mechanical side. Or.....I'm going with the starter is overheating.
For $20 go to o'reilly get the DEI or equal insulated thermal sheild and warp it around the starter. I did this as a precaution, my headers are extermly close to the starter. You could buy an infared gun and measure the temperature of the starter when it doesn't start. You could pull the starter after 20 minutes and support it with wire if possible and turn the ignition switch or disconnect the postive cable and lay it on the floor, positive jumper cable to the starter post and other side to the positive pos on the battery, negative cable to the body of the starter, stand on the starter and touch the negative side to the battery. If the starter spins but really weak it's heat related. Don't foreget the safety glasses.
Get a light and examine the exhaust around the starter.
I picked up the DEI insulation wrap from O'Reilly's today and installed it. There was enough left over to wrap my fuel pump so I'll do that also. Here's some pics of the exhaust collector/starter clearance. Didn't have time to drive it today to test it though. I'll let you know how it works.
Drove it for about 30 minutes today and got it up to operating temps. I pulled back into my driveway (getting smarter), turned it off and tried to restart = no go. The starter engages but bogs down immediately. With the starter wrapped, the temp of the center of the starter (facing front of the engine and exposed) is 180* and the temp of the starter solenoid (under the wrap) is 230*. I did not install the dedicated ground wire to the case/mounting bolt yet.
The engine seemed to be lagging in 3rd again and it also backfired through the tbi once.
Well.....if adjusting the timing does not work....Let's check voltage. Do you have a volt meter? Let the jeep cool down. Connect the volt meter to the battery, red (+) to positive and black (-) to negative on the battery. Record voltage. You will need a helper or if you have long enough leads to streach into the cab so you can see what happens. Start the jeep and record how much the voltage dips, it should return to 13-14 volts. Then turn the head lights on while watching the volt meter, it should dip and return to ~13-14 volts, record, turn the brights on and record, turn the heater motor on high and record. Now with all this running watch the meter, does the voltage stay at 13-14 volts steady or does it start to drop off. Watch for 5 minutes. Record your findings. Do you know the amp rating of your alternator?
Go for your 30 minute drive during the day without the lights or blower on. Come home leave the engine running, hook up your meter to the battery and watch the voltage, is it steady? Again turn the lights on, then the brights, then the blower in one minute increments. Record your findings.
Shut the engine off. Try and start and watch the voltage. Does it dip and how far. We are trying to isolate the problem. Alternator, Battery, Soenoid, Cables, Grounds. Thats assuming something mecanical is not binding up . Record each finding and and save for now. Write down observations.
Not to assume the worst case scenario, but when you assembled the motor, was the torque wrench that you used accurate? Additionally, did you ensure that all bearings and rings were the appropriate oversize for any machining you had performed? It just sounds to me like once things heat up something is getting excessively tight.
Thanks for the input guys. I'll mess with it again this weekend and report back.
Things I know:
The alternator is a new 95amp unit.
The volt gauge is steady at 14v while driving, even after the contour fans kick on. (I'll test with lights and other accessories this weekend)
The machine work was done to match the parts in the engine kit or so i was told, it was my first time using this machine shop.
The torque wrench is fairly new and only used one other time on my other 401 engine build.
I can adjust the timing back down to 8* and see if that helps any. I will also buy the header wrap and wrap my exhaust manifolds.
I only have 11 miles on the engine so far if that makes a difference.
Hot oil pressure at idle is 40psi and under load is 60psi.
Ok, exhaust manifolds are wrapped in DEI Header/Exhaust wrap and the starter is wrapped in the DEI starter wrap with the extra piece doubled over the solenoid. I wrapped the right side manifold with two layers. That stuff is expensive.
I bumped the timing down to 5* and took it for a drive around the neighborhood. The outcome is that I have less power, also the starter bound up again when I tried to restart it with the hot engine. I think I'm trying to set my timing to some cookie cutter number from a book instead of listening to what the engine is telling me. I've been reading up on timing on the AMCforum and will add more advance in because most of what I read says to be in the 12*-18* range. I'll also add the ground wire to the starter case.
I was out of town for a few days but I finally got a chance to read up on timing. I tried both the timing light and the vacuum gauge methods and road tested after each adjustment. The timing light method worked best and I wound up at 18* BTDC. The power is back and the hesitation/stumble in third is gone. I made the adjustments with the engine at operating temps and road tested up a grade under load, no ping. I'm gonna leave the timing the way it is and focus on my 'no hot restart' issue.
I turned on the headlights and all accessories while driving and my volt gauge reads a steady 13v (even with the dual contour fans running).
I installed a ground cable from the starter to the - Battery terminal and also sleeved the + and - starter cables along with my alternator wiring in DEI insulation wrap. The plastic wire loom was melted off the alternator wiring because it's near the passenger side exhaust manifold. If this doesn't solve the no hot restart issue then the Jeep is gonna sit in the driveway for the summer while I work on my 79'.
It was in the 60's today so I took the Jeep for a drive to test it out. With the significantly cooler weather combined with all of the insulation plus the additional starter ground cable, the Jeep restarted while hot. The starter lugged but was able to turn it over. I call this a mini-success. I'm done with it for now.