Hi everyone
(EDIT - TITLE is wrong.. it is cylinder 6 which is not firing)
Spent the last 2 weekends rebuilding this 1974 FE360. The engine runs rough and we've discovered that cyl6 is not firing. I know the plug and wire are good, we've go the right firing order. After running the motor the plug is gassy. As you can see from the pictures below, since rebuilding this motor and running it, the cyl has never fired. We have confirmed that we have spark. When I removed the distributor the gear which meshes with the cam had several holes and locking pins in it. It appears that the gear had been replaced by the previous owner. Would it be possible that the shaft on the distributor is slipping each time at cylinder 6 and the spark, while apparent on our inline plug tester just isn't aligned with the compression? I'm at a loss here.

Really looking for thoughts and advice on this.

Thanks!!

cyl 6 has never fired since rebuild

Clean one is the no-fire of course

 

I'd make sure the cam lobe is OK. Valve cover off, crank and watch for a rocker that doesn't move right.

 

I agree with you beartracks. When we rebuilt this engine we inspected the cam and it looked good. We installed new flat tappet lifters but reused the push rods. I rolled the motor over by hand with the valve cover off and watched and the valves moved similar to other ones. I did not crank it... but can for sure.

 

If you used the old cam and new lifters you should be okay, but still run zinc.

It would be nearly impossible for the distributor gears to do that, and even if they did the cylinder that missed spark would change one hole every 2 revolutions since it skipped 1 cylinder each time. I'd forget that.

You can have spark but if it's weak it still may not fire, does the spark jump good and have a blue color? I would try a different plug wire just for grins, and I would air it out good and put a new plug in if you haven't already.

If the valves look like they're moving like the rest of them I'd check the compression in that hole. hard to imagine a cause but when nothing makes sense you look at everything.

 

Pull the dizzy cap and check contacts.

When you turned the engine over by hand, were the spark plugs installed?

Just wondering if full pressure may be showing a weakness in the valve train?

I don’t suppose you also reused springs, or did you verify both valves are closing?

Fuel, compression, spark.

 

1st thing I would do is after you established you have fuel and spark is run a compression test on the cylinder that fires vs the one that is not. That will tell you a lot about what's going on. Then check the spark of a cylinder that's firing vs the one that's not. See if it weak in comparison.
good luck keep us posted

 

HI everyone
Thanks as always for this advice.To answer questions, we did use the same valve springs but replaced valves and seats. When we rebuilt the heads each cylinder sealed by vacuum test perfectly. Yesterday I rolled the engine over by hand and the valve rockers appear to move similar to others, so I don't think that's the cause. I will roll the engine over with the starter to see if that's any different. When we replaced the cylinders the pistons were within spec as were the new rings as well as the cylinder. I hope a compression test will show similar compression across that bank and I will do this tonight.

When I pulled the dizzy (after my original post yesterday) the glaring thing I see is that when the dizzy is on the bench, if I hold the rotor and the gear, I can turn the two parts in opposite directions about 5 degrees. It's like there's slop in the rotor and shaft. I think this is a combination of the old shaft, the gear attachment mentioned earlier and the top of the shaft where the rotor attaches. Am I correct? there should be next to no play is this?

I'm really leaning towards replacing the whole dizzy. I know there are lots of junk knock-offs out there. I'd like to get a regular point/condensor model and than add the pertronix kit I already have. Does someone have the part number for what this distributor would be stock?

Thanks fellas - really appreciate talking this through with ya!

 

Using new lifters on an old cam can be problematic. I'd make sure all the push rods are properly seated. Compression test should tell you something.

 

Check to see if you have compression on that cylinder. If it doesn't this can be caused by a lot of things.

 

I agree with the above on compression test, AND check the plug, I've had many numerous "new" plugs cracked along the ceramic, didn't notice till troubleshooting at night, saw the nice blue arc to the head every time... OR, you can get brave, and while the engine is running, slowly run your hand down the plug wire to the plug and see whatcha get it'll bite, but you do find the problem

 

That's a good idea about the plug. I had that happen a few years ago on an engine that I had on the dyno. I had run it quite a bit and then changed the plugs, suddenly it had a miss. I ohmed out the plug and it was open.

 

HI guys

So I ran the compression test. Just as a bit of background, I used my picoscope with wps500 pressure transducer to complete this test. This is the coolest tool I own and is super accurate. I can share waveforms if anyone would like. The following numbers are an average of 4 compression episodes on each cylinder. Anyway, here's the results

This test was done cranking
cylinder 1 - 107.4 psi
cylinder 2 - 112.3 psi
cylinder 3 - 112.2 psi
cylinder 4 - 112.0 psi
cylinder 5 - 114.3 psi
cylinder 6 - 104.8 psi
cylinder 7 - 106.8 psi
cylinder 8 - 110.5 psi

As stated earlier, cylinder 6 is the problem cylinder which has never fired. While there are some variations in the pressure values there is not the massive difference of a mechanical dead hole.

So, I believe I'm back to plugs, wires, distributor. My dizzy is the OEM one with what looks like a replaced gear. I've installed a pertronix 40111 1.5 ohm coil and a pertronix 1281 ignition conversion without any resistors as per pertronix tech support direction. When I checked spark yesterday I had a simple inline spark plug test light I use on my snow blower and lawnmower (nothing fancy). It showed spark but I don't know how strong a spark I have with this setup. Does anyone have any values on spark? The pertronix coil says 40,000 volts but I don't know anything else.

Thanks as always!

 

That play is the advance mechanism in the distributor, that is normal.

Since you have some compression, I am with the others, try a different plug, and also verify that your firing order is correct.
Is your carburetor is good order? Those manifolds and ports look awful sooty for something that hasn’t ran very long.

 

also check for any vacuum leaks that would affect that cylinder...intake manifold gasket, vacuum fittings in that runner, etc...

 

Thanks for this - the carb was rebuilt last fall but has only run about 20 minutes (15 before we removed and rebuilt the motor so while it's all new holley parts, it has not been tuned to any great extent. When we realized 1 cyl wasn't firing we stopped running the motor. The manafold was clean when we started so I agree.. fairly dirty.