Remember it takes two complete revolutions of the crank to cycle through all four strokes, (720 degrees).

The mark on the harmonic balancer will point to the scale at TDC of the intake stroke, and again at TDC of the compression stoke.

It must be at TDC of compression stroke of #1 piston.

With #1 plug removed, stick your finger over the hole and crank the engine until you feel air shoot out. That will get you into the ball park of TDC of compression stroke. Then move the crank by hand, and point the mark to zero. You should only have to move it a little bit.

 

The problem is though I'm feeling compression at both the exhaust stroke and the compression stroke so I'm not sure which stroke I'm actually on. My finger isn't really fat enough to completely plug the hole so I can't tell which one is actually the compression stroke by doing this.

 

Maybe you could place the plug in the #1 hole with a thread or two. When the piston is coming up on the compression stroke you will hear the air pressure coming out the hole. Stop when you start hearing the air pressure coming out and continue turning the engine by hand in the same direction either using just the belt or turn the alt pulley.Once the timing mark lines up with the pointer, insert a piece of coat hanger bent to go into the cylinder. I t should hit the top of the #1 piston which should be right up there. If it is not up there,the timing mark section on the pulley may have spun some.
If everything is as stated, that rotor should be now be just about at the #1 plug wire terminal on the cap. You can't keep switching the dist that 180 degrees and hope to get it right. You seem to know the procedure and with all the suggestions from the members you should be able to either get it running or find the problem. You can do it !!

 

Put on a pair of gloves, and just tap the starter over until you feel compression push air out of the cylinder. Or use a compression tester. Then set the crank mark to zero. The rotor of the dist. must then point to #1 cylinder on the cap. Not #6 cylinder. (Some dist. caps have a number 1 marked on them.)

You shouldn't feel any compression on the exhaust stroke unless the valve is not openning. Which I doubt.

 

to find out if it,s in time is by getting number 1 piston all the way up, turn the crank until it shows (0 ) on the timing scale and check the rotor button ! the rotor should be pointing to number 1 plug wire on the cap ! if you just have 1 or 2 plugs not firing then it could be the distributor cap or some of the plug wires are bad !

 

Looks like its the timing chain.

 

Ah, well, that would sure throw the timing off. Bummer. But, I'm glad you found the problem.

Do keep us updated on the progress. Be cool to see a pic or two of your truck too, and that 390!

Cheers.

 

if you do put a chain in it just remember to mark the dist. before you pull it back out cause if you don't mark it it'll be off one tooth or maybe even two both of which will give you a headache

 

I'm thinking about just taking it to a shop, this is giving me a headache. Especially considering I'm not 100% that it's the timing chain.

It was running so good.. and now I can only get it to backfire.

 

There is another way to find TDC of the compression stroke of #1 piston.

Remove the valve cover on cylinder bank, 5-6-7-8. Driver's side.

Turn the crankshaft by hand and watch cylinder #6 intake valve.

Right when cylinder #6 intake valve just begins to open, and I mean you just barely begin to see that valve open, the #1 piston is near TDC of its compression stroke.

Look at the timing mark. It should be near the zero mark on the scale. But you will need to move the crank some, since the valves have a certain amount of overlap.

The reason this method works is because the 390 is a four stroke, even firing engine. It fires every 90 degress. (90*8=720. Two complete revolutions of the crankshaft for all eight pistons to complete their four stroke cycle. One complete turn of the cam.)

An even firing engine means each piston has an opposing piston that is in the same place in its cylinder bore at all times. In the case of the 390 the opposing cylinder of #1 is #6.

The rotor on the dist. turns counterclockwise. The firing order is 1-5-4-2-6-3-7-8. The cylinders are from front to rear, passenger side 1-2-3-4, and driver's side 5-6-7-8.

Once you find TDC of the compression stroke of #1 piston the dist. cap only fits on the dist. one way. Install the dist. so that the rotor is pointing to the sparkplug wire of #1 cylinder on the dist. cap.

Upon start up attempt have some one crank the engine and turn the dist. advanced and retarded a little while the engine is cranking.

It should fire up. As long as the timing chain hasn't jumped, it's getting spark, and it's not flooded.

Cheers.