Hello to all. I am having an issue with getting my 1996 GMC 1500 Sierra truck (4.3l Vortec) started after a piston ring replacement. I have verified all of my wires have been properly replaced, I have spark, and I can smell gas so I am assuming that I am getting fuel. The truck turns over, albeit very sluggishly which I am assuming is because it has not gotten any oil yet since it has not started. I made sure my timing was set by making sure of the TDC for cylinder #1 and lined up the distributor appropriately. My father in-law seems to think that my engine could be 180 Degrees out from my distributor. I do not know much about this but if the cylinder fire only once out of two rotations, he thinks that my distributer if firing on the exhaust stroke vice the compression stoke. Is that possible, and if so, How would I go about fixing it. Thanks in advance for your help.

I've learned the best way to find #1 TDC with these 4.3'* and 5.7'* is to remove the drivers side valve cover, rotate the engine by hand to TDC indicated by the harmonic balancer. Now, the #1 exhaust and intake rockers should be loose to the feel. If they are not, rotate the engine until this happens. You have a 25% chance of getting it right the first time.

Once TDC is found, now reinstall your distributor so that the rotor is now pointing to cylinder #1. You may need a long flat head screw driver to readjust the oil pump drive shaft inside the engine. Its a pain in the *** sometimes.

Let us know how it goes.

OK, so I know where TDC is due to the marks on the belt wheel and mark on the engine block. I went ahead and set it TDC on #1, removed the distributor shaft, rotated the engine one revolution, and reinstalled the distributor shaft. Then after trying to start it, it was turning over much better then it did before, but it is still not starting. I am getting spark on the plugs and I am getting fuel. What else could be the problem?

That'* not how its done, nor the way I instructed you to do it. You need to actually FIND TDC. Simply rotating the engine so the pointer is showing TDC is not enough, like I said, you have a 25% chance getting it right the first time. You need to make it so that #1 piston is on the upwards travel of the compression cycle. This is where removing the valve cover is essential in determining which cycle you are on.

Got it. So before I do this, do I need to remove my distributor again and reset where the rotor is at, or can I just adjust the rotor when I find TDC?

I'll put it into steps based on the work you have done so far.

Remove distributor cap.

Remove drivers side valve cover.

Rotate engine until the TDC mark is at the pointer. Now, wiggle cylinder #1 rockers. If they both move, you should be at TDC. They wiggle because both valves are closed and no pressure is exerted from the valves.

Now, pull the distributor out until the gear freely spins. Rotate the rotor so its either before or after #1 spark plug. You may have to experiment with this because when you put the distributor back into the hole, it will rotate the rotor.(which direction, I don't remember) So when you do this, you need to compensate for the turning. Basically, when this is done correctly, the rotor tip should be pointing at #1 on the rotor cap AFTER the distributor is fully seated.

Reinstall everything, and attempt to start.


There is a lesson to be learned here. When you had the engine torn apart, you should have noted where TDC is, or at least put it at TDC before closing the engine up.

I have one more question, this one if for my knowledge. while rotating my engine and watching the rotor, the rotor turns 1/2 evolution to one full turn of the balancer wheel. Wouldn't I have a 50% chance of getting it at TDC on the compression stroke? Where does the 25% chance come into play?

Yep, your right. It'* 50% chance. I was thinking 25% because of it being 4 cycles. So, because if its still not right, you can rotate your distributor 180* and it should line up on the other 50%. If you catch my drift.

All is well. I guess I had a couple of issues (self induced). After scratching my head numerous times and looking at articles on the internet, I realized that my balancer wheel had two marks on it, and I was lining it up with the wrong one (I can't get a 50/50 choice right the first time to save my life) But after figuring that out, and rotating the distributor 180 out, it finally started. I greatly appreciate your help in this matter. I learned quite a bit going through all of this.

Your welcome, glad we could help.