ok let me try and give all the info on what I have done. I bought a rebuilt long block from NAPA last year in June. I put the motor in and all was fine. I noticed a slight miss a few months ago. I figured it was the old 2100 carb I put back on it after the install, EVERYTHING about the firing system was replaced new when I put it together.I took a carb off a buddy's truck yesterday that runs fine but my truck still had 1 and 6 not firing. I have confirmed the sparkplugs are firing on 1 and 6 but those cylinders are dead. I did a compression check and got 120 -140 on all cylinders. I pulled the valve covers ond dont see anything out of ordinary. I was thinking maybe valves but if it had a valve was stuck open the compression would be nothing. If its stuck shut, wouldn't the pushrod be bent? I'm stumped I think I still got warranty on the motor it doesn't have 10,000 miles on it

 

Rotate the motor with the valve covers off. See if the pushrod is actually being pushed. Wiped cam lobe could be round by now, not lifting the valve anymore.

 

Yes it's moving up and down just like the rest.

 

Vacuum leak at manifold/head. These usually suck oil, but not always if it is on the underside. Try the WD-40 (or other) spray around the manifold gaskets. Tough to do on an FE, impossible to do the undersides, but it's something to check.

 

I just checked the compression again.
1. 150
2. 150
3. 145
4. 145
5. 145
6. 150
7. 145
8. 145

There isn't any way I could have valve problems with those numbers, correct? Should I just change intake gaskets and see what happens? I don't know what to do.

 

Try switching the plugs around, see if the miss follows one of those plugs. Sure, they spark with you have them out, but under pressure they could misfire. Unlikely, but not impossible and easier than the intake thing.

You aren't sucking oil, right?, no puff on decel or anything like that? Any fouling on the plugs?

 

Looking at the runners in the intake manifold, any chance that there is a manifold vacuum take off near cylinders #1 or #6?

Back in the early 80's I had a heck of a time with a '71 Chevy 350 two barrel that I had just changed plugs/wires/points on. Ran like crap when I was done. Back then, it was easy to roll up the spark plug wire boot at the distributor on all the wires, and ground each of them out one a time with a wire to ground, to see which cylinders when shorted out would/would not drop idle RPM. I found one back cylinder totally dead (no effect on RPM when shorted), and one cylinder towards the front on the other side of the block half-dead (slight effect on RPM when shorted).

After much part-swapping and hair-pulling to no avail, I noticed that the dead and half-dead were on opposite sides of the carb, but the runners were inline across the carb... hmmm. Then I noticed that the back cylinder's runner had a vac take-off, a rubber hose to the AT's vacuum modulator. I found the underside of the hose had a split, so it made that cylinder so lean it couldn't fire. And the extra air also seemed to get to the cylinder inline across the carb too.
The hose had turned to stone, and I guess I bumped it somehow changing stuff, and it split. Could not see it being underneath, could only feel it.

Just a thought, insidious vacuum leaks.

 

I found the problem but what I don't know is why it happened. The top of the valve stems where the rocker arm touches is worn on the 2 dead cylinders. What causes this?

 

On shaft mounted rockers you can't misalign things as easily as studs. (like if your buddy had you thread them by hand and one was a little crooked and started to squeak and you had to pull the heads and you were glad you put those little ceramic magnets near the oil drains...don't ask me how I know this)

I suspect something cracked or otherwise broken. Wag alert.

Stand by, as others know more and they know it better.

 

This is just an educated guess, but I'm betting that the tops of the offending valve stems had been ground in the rebuild process to offset the grinding that took place on the valve seats for those valves. This is sometimes done to maintain the clearance at the top of the valve stem, but if the rebuilder grinds through the hardening at the tip of the valve stem, the stem will wear prematurely once installed. Saves the rebuilder the price of a new valve seat, and the gamble is that the ground valve stem will outlast the warranty period. Again, just an educated guess.


Good luck,
Jay

 

How much wear are you talking about? I just can't imagine enough wear to cause a cylinder to go dead...

 

I guess something easy to check would be to start it up and run it with a valve cover off, and see if the offending valve is getting oiled, or if something's plugged for that position.

You could get a set of the metal clip-on oil deflector clips that clip onto the rockers to restrain oil from flying around with the valve cover off, if you don't want it to get too messy.

You could also pull the distributor, and drive the oil pump in the proper direction with a drill, but you would have to get it up to reasonable RPM against the oil pump's increasing resistance to see anything useful.

 

A bit of wear is nothing. These are dino engines. A few things to try. Swap the rocker set from one side to the other. Swap wires one side to the other. Also when the rocker shafts are off take a square across the tips of the valves see if some are low/high. Could be mis-machined. Just things to look at. If anything looks suspect take a pic and post it here. We can help ya.

 

I've had the motor running with the valve covers off. I see nothing obviously wrong. I've done the swapping of plugs and wires. It stays the same 1 & 6 dead. Iron Clad engine wants me change the intake gasket and see what happens. If it's still the same and I really believe it will be. It goes back to them.

 

I don't know what exactly the problem was but Iron Clad engines sent me another long block. I installed it last weekend. She is running like a champ. It was something internal as I have the same wires plugs etc. on this motor.