Hard Cranking When Hot

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Warneir

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’72 440 HP
11-1 Compression
68 426 wedge heads shaved .020


The Issue: The engine fires with no problems at all when cold. Cranks like mad and starts right up.

When it gets hot or has been running for 10-15 minutes it is very hard to start. You may get ½ to 1 and ½ cranks on the engine and it does not turn. Cranks very hard when hot.

I just replaced the starter thinking it was taking major “heat sink” and may have had a dead spot in it when hot. This did not resolve the issue.

Have played with the timing a lot! Advancing and retarding the timing does not seem to help at all. (Was thinking it may be firing before TDC.) (Even removed the vacuum from the distributor to play safe.)

Posting this for any Ideas out there. I know someone has probably had this issue before.


Other notes on the issue:

The battery is trunk mounted. It is a 925CC battery. Welding cables have been used to supply the power to the front.
 
hOW LONG HAS BAT. BEEN IN TRUNK ? dID THIS SRART WHEN YOU MOVED BAT? your cables may not be large enough to carry enough amperage to the starter. Or your engine could be going sour.IMG]
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If changing the timing doesn't affect it, it has to be battery cable caused. A lot of cars that have a lot of initial timing have this problem. One solution is a ignition box that has a start-retard feature in it.
 
I bought the car in 94. It was in pieces when I got it.

I built the engine from the ground up. I have only put about 1500 miles on it in 10 years. (This car sits in the garage and collects a lot of dust.)

The battery has been in the trunk since I put the car together.
(The first battery ended up part way in the power steering pulley. The plastic mount that was used under the hood didn’t hold up to the header heat very well.)

The welding cables are very heavy. I made sure to get a large gauge wire for the CC AMPs they needed to carry. Much larger then your standard battery cables.

I have started to consider the fact that it may be a fuel vapor issue.
Heavy fuel vapor sitting in the cylinders/manifold maybe causing a compression issue? (I found an article about this, but not sure if that’s the case, and there was no reply as to if it helped.)

Someone suggested that when the engine is shut down the fuel in the carb is expanding from heat and running into the manifold. So setting the floats lower may help.

But it is instant in my case. I can shut the car down and instantly try to start it. I get the ½ crank and stop.
 
I will get a set of battery cables and see if I can do a test in the driveway with the battery up front.

Another thought would be the cable from the solenoid to the starter, or the solenoid itself.

Thanks guys for putting some more Ideas in my head. I will try a few things and let you know what I find out.
 
+ cable is a 1/0 welding cable = 0.580 inch diam.

Standard + cables are 4 gauge wire = 0.310 inch diam.
 
Also check to make sure your gas cap is venting properly. If you pop the gas cap after it's hot and get alot of pressure release it may be causing the compression issues you spoke of. I just recently troubleshot two blown diaghrams in two new mechanical fuel pumps on my 454 chevy(yeah I know, It's for sale now)The pressurue would get so high it actually prevented the engine from turning over, I replaced the battery too thinking it was a battery issue. In the end it was the gas cap vent was stuck closed. I never would have thought that a fuel pump could lock up a motor.....but it did. I also had to drain the oil both times since the blown diaghram poured gas into the oil pan while I was cranking it over.good luck finding the culprit.
 
My '65 Barracuda has been doing this for about 2 weeks & we just spotted a possible cause last night - 2 of the spark plug wires are melting! It was hard to see because it was on the underneath part. Working on that today......
 
your cables may be large enough, but how old are they? copper does oxidize causing ohms of resistance...
also if your carb is leaking fuel into the engine u should be able to see smoke rising out of the carb. (this wouldn`t keep your engine from cranking regardless)
definitely test the starter and insulate...
 
check ur grounds make sure they are clean and tight i run my batt in the trunk also had to up size my ground from engine to frame up front to a nice large braded strap works great now
 
I had the same issue here in hot Florida. I have 10.5 compression. Wrap your starter well and get a strong good battery like Optima but something with quality power.
It made a big difference for me.
Good luck.
 
As I read it, the battery is 10 yrs old.?? The avg life expectancy of a lead/acid battery is 5 - 7 yrs, so that's be the first thing to check. It could read 13+ volts, but have no "capacity" to crank.

If I hadn't read the 10yr thing, My first thought was strongly recommend trying another starter. For the full sized starters, a lotta rebuilders just dissmantle and toss a buncha mopar starter parts in a cleaner, and re-assemble generically into one part #. So that replacement starter may have had a less than "440" suitable armature.

I'd try a different starter regardless, hopefully suitably assembled.

Been where you are, a few times, that was the cure. ( ^#@$&*^) lol

hope it helps. cheers
 
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How many and where are your grounds and how big are those cables? 1ga for the positive is pretty big. I would use the same for the main negative going to wherever it grounds off the battery. Then a minimum of 4ga from the engine to the chassis. One to the frame rail, one to the radiator support and one to the firewall. Make sure where the grounds are attached is CLEAN as can be. RIGHT down to bare metal.
 
While pondering if the battery or cables is good for possibilities. A simple voltmeter check while cranking provides usable information.

Voltmeters draw very little current, so leads can be extended to measure voltage drops in cables, and other places, like at starter, at remote location so you can see while cranking.

Starter motors are DC motors. The maximum torque is when they are stalled, but it is limited by armature current. Neglecting losses, the peak power is volts times current. So with poor connections, current is limited, and voltage is reduced, hence less power to crank at starter motor.

Acceptable voltage drops are a few tenths of a volt, more than that, is a problem. The voltmeter provides a way to evalutate, and improve connections.

If you have lead lugs, consider changing to crimped copper. Welding cable may not meet all the specifications for automotive starter cables. It has fine strands, if oxidized it may not be possible to make good connections.
 
^^THIS^^ Get a voltmeter and do some checking. You must determine if it's the battery, the cables or the starter, or (gag) something dragging in engine bearings

MOST LIKELY is starter

Get yourself a voltmeter, and if possible a LOAD TESTER, a BIG load tester like one of these. Beg, borrow, etc

carbon-pile-tester.jpg


You need to figure out where you are losing voltage, if that is the problem, and how much current the starter is drawing. The way you do this with a load tester is to crank the starter enough (few seconds) to get a stable reading on the tester voltmeter. That reading shows how much the starter is dragging down the battery. Then you crank in the carbon pile until the voltmeter matches that same reading, and then read the amperage draw.

This is complicated by the trunk mount. you need as suggested above, to get a long length of no 18 or larger wire to reach from front to back of the vehicle. you can clip one lead to the starter stud, through the meter (voltage) and clip to the battery positive post. Crank the starter and take a reading. You are hoping for a very very LOW reading the lower the better. This tells you if you have excessive drop on the cable.

Do the same with the ground side. Clip to the engine block, run through the meter, go back and clip to the battery NEG post. Crank the starter, read the meter. Same as above. Lower the better.

Most guys on here know I don NOT like "throwing parts" (and money) at a problem. If I have to take a guess, in this case it would be a bad starter
 
I had this issue for years on my Jeep. I replaced the starter and battery with no luck. I went through and replaced most of the ends on all of the power cables and the issue went away. I think I had internal corrosion in the ends prevent current flow.
 
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