Pre-ignition / starting problem. Ripping hair out.

[Blue85]

Need to prove the timing marks are correct and the balancer and timing pointer are matched.

Exactly what I was going to say. This fight will only be easier if you know the true timing.

Start by proving TDC

Yes, go check the timing manually like has already been suggested multiple times in this thread.

Have to verify the timing marks.

 

[78 GMC Jimmy]

If I am timing the engine by hand without a timing light, or timing the engine with a vacuum guage, then the timing marks don't matter, Correct? I retard the timing too far and the problem remains. Then I keep advancing it until its advanced too far and the problem is still there. No matter where I set the distributor the problem remains. So I'm not sure why verifying the timing mark matters. Please explain.

 

[78 GMC Jimmy]

Confirming that the #1 is at top dead when the timing marks are at zero. That's what I need to do? Put something into the cylinder and make sure it pushed out the farthest when at 0 degrees? This is to check if the timing chain was not installed with the timing marks lined up properly? Correct?

 

[Wes Harden]

Yes you want the #1 piston at TDC. This requires a little work to do on an assembled engine. Put the above tool in the spark plug hole, gently turn crank by hand till you hit stop. Mark the balancer ring. turn the crank the opposite direction until it stops. mark the balancer. the mid way point between the 2 lines is TDC. We don't suspect the timing being installed wrong, we suspect the balancer outer ring has slipped and is lying to you.
For stabbing a distributor you want #1 TDC compression stroke. If by chance the balancer had slipped when the distributor was stabbed, you would have difficulty timing the engine. It is close or wouldn't crank well when cold.
Slow cranking when hot is not unusual for our squares, but normally an electrical issue in the cranking circuit. Not sure how many of us have disabled the ignition when slow crank was happening. Those with ignition kill switch maybe can test this

 

[78 GMC Jimmy]

Yes you want the #1 piston at TDC. This requires a little work to do on an assembled engine. Put the above tool in the spark plug hole, gently turn crank by hand till you hit stop. Mark the balancer ring. turn the crank the opposite direction until it stops. mark the balancer. the mid way point between the 2 lines is TDC. We don't suspect the timing being installed wrong, we suspect the balancer outer ring has slipped and is lying to you.
For stabbing a distributor you want #1 TDC compression stroke. If by chance the balancer had slipped when the distributor was stabbed, you would have difficulty timing the engine. It is close or wouldn't crank well when cold.
Slow cranking when hot is not unusual for our squares, but normally an electrical issue in the cranking circuit. Not sure how many of us have disabled the ignition when slow crank was happening. Those with ignition kill switch maybe can test this

I had an friend listed to it, and he said its 100% a timing issue. He is an old school SBC engine builder. He said that going to a 160 thermostat is a last ditch option and that I should replace the entire distributor first as one final option to try. I could verify the timing marks at the same time.

 

[Wes Harden]

You really need to verify the marks, before you stab a new distributor, or any distributor.

 

[78 GMC Jimmy]

You really need to verify the marks, before you stab a new distributor, or any distributor.

To play devils advocate - If I tried using a vacuum gauge to time the motor, and I'm not using a timing light at all, why verify the timing marks?

 

[78 GMC Jimmy]

My plan is to line up the number 1 cylinder to TDC by letting the pressure blow my finger off the spark plug hole, which should land the mark near zero. Then turning the motor a little bit to achieve the zero lined up to the mark. Then I plan to drop a new distributor in. If that doesn't fix it, then running at 160 degrees is the last option. Correct?

 

[RaisedK5]

To play devils advocate - If I tried using a vacuum gauge to time the motor, and I'm not using a timing light at all, why verify the timing marks?

Because then you can see what timing is doing under different conditions. If it jumps around then you have slop in the timing chain. If the mechanical advancement is hanging up you can see when the distributor is stuck advanced. You can see if the advances are working and how far the advance is advancing. etc.

 

[78 GMC Jimmy]

Because then you can see what timing is doing under different conditions. If it jumps around then you have slop in the timing chain. If the mechanical advancement is hanging up you can see when the distributor is stuck advanced. You can see if the advances are working and how far the advance is advancing. etc.

Makes sense.

 

[Wes Harden]

vacuum gauge will not prove the distributor is installed correctly.

 

[Wes Harden]

there is 90° + of rotation that pressure can be felt, to much room for error. You ask for advise and we provided, but you seem to want to do things your own way. Hows that working out for you ??

 

[78 GMC Jimmy]

there is 90° + of rotation that pressure can be felt, to much room for error. You ask for advise and we provided, but you seem to want to do things your own way. Hows that working out for you ??

I hear ya. That's why I was running the method by you first. If the way I mentioned wont work, then I will not attempt that method.

 

[Blue85]

I'm not using a timing light at all, why verify the timing marks?

If you read through this thread, the guys here have already spent more time advising you on this than it would have taken you to do this very basic check. We can all back out and spend time helping somebody else instead if that's what you want.

 

[78 GMC Jimmy]

OK, it has been confirmed that the timing mark is correct.

 

[78 GMC Jimmy]

Is there any reason not to hit the vacuum advance weights and springs with WD40 or oil in order to ensure that its not hanging up? Could you put a little oil into the hole on the vacuum advance at the distributor, like where the vacuum hose connects to? I assume the oil will get flung off for the moving parts, but would that short out the sparks from the rotor? I could heat up some dielectric grease and use that, but I'm concerned that it would be too thick in cold temperatures and restrict the movement of the parts.

 

[78 GMC Jimmy]

Screw it. I ordered a complete new distributor for $50 on Amazon. Lots of good reviews on it, so hopefully it will work properly.

So with a new distributor, verified timing marks, proper type and gap plugs, if it still doesn't work properly, is there anything left to check? Or do I just go with the kill switch idea and leave the distributor off until the motor is spinning good and then flip the switch on to start the engine. The only other option that I can think of is the 160 thermostat to keep the engine cool enough that the symptoms don't reappear.

 

[dyeager535]

160* thermostat for a slow cranking hot engine seems an...odd...choice to try and solve. I can see that to try and pull as much heat out of the intake as possible to keep a carb cool, it's going to do virtually nothing for anything that isnt tied into the cooling system well.

The intake has coolant flowing through it, thus it will pull heat out of the metal quite effectively. A starter and electrical components aren't going to benefit from a colder thermostat at all.

The trucks came with a 195* thermostat for decades and didn't have systemic slow crank hot start problems, thus it can be reasonably ascertained that your problem is not the coolant temp.

Heat can affect starters and electrical components, but that isn't something you attempt to control through coolant temp. Exhaust temp is upwards of 1000*, manifold temp can be in the 300* range, to give you an idea how much heat we are talking, that generally a thermostat change will have extremely limited impact on.

 

[bradshawtech]

Did I misread something, have we checked out the starter or battery cables? I never saw any videos of the starting performance cold, hot and with the kill switch.

voltage tests cold, hot, under a load?

 

[78 GMC Jimmy]

Electrical:
The engine cranks over great when the distributor kill switch is turned off with the stock starter and with the high torque gear reduction stater. If the engine is cold, it will crank over great with the kill switch turned on or off. Once its fully up to temp and the thermostat is open, the engine will not crank over properly. Turns VERY slowly until it starts. If you flip the switch off, the cranking speed returns to normal. If its cranking super slow, and you just walk away from the vehicle for an hour and then try again it will crank over and start no problem. It appears to be pre-ignition when hot. The starter has a custom heat shield over it and the battery cables tested good. Its not a problem with the battery, cables, or starter. The kill switch and other tests confirm it.

As for installing a 160 thermostat, same reasoning. When its hot and the kill switch is not in use, it wont turn over very well. Let it cool down and it cranks great. So if its not the starter or electrical problem, then what?

I had a Nissan once that would start and run great. Once it got up to temp, the engine ran terrible and was hard to start. What was the problem? I have no idea, but after pulling the thermostat it started and ran great every time. No idea why, all I know is that it worked cold and not hot.

As for why my engine is getting per-ignition when hot? I have no idea, that's why I came here.

Installing the new distributor today, unless anyone has any other ideas.

Note: I am no expert, but I am a mechanic. I have two friends that are both retired mechanics (one was an engine builder). All three of us are stumped. We all agree that its pre-ignition when hot, for an unknown reason. All three of us have never seen a problem like this.

These videos were taken when the engine is hot. One time it starts fine with a knock or two. The other time it cranks super slow. .