Finished my rebuild for 351w. Went to start it up, didn’t start only cranked. Made sure it’s timed right and getting spark, fuel. Did a compression test and might have found my problem. Here are the readings:
cylinder 1: 0
cylinder 2: 0
cylinder 3: 75
cylinder 4:0
cylinder 5: 90
cylinder 6:0
cylinder 7: 150
cylinder 8:125
First rebuild so it’s a little discouraging. What could be causing this? New piston rings, just got the block and heads worked on. What should be my process to diagnose this? Pulling off the heads, checking valve leaks, piston ring gaps, what else?

 

Original push rods now too long. How did you determine push rod length?

 

Improper valve lash has been the main problem on the last few rebuilds in here.

Your Ford does not have a adjustable valvetrain, unless it's been modified with hardened pushrods and guide plates with screw in studs. If yours is original, you just have bolts that you tighten for the rocker arms.

You can check the valve lash by taking the pass side valve cover back off, turn the engine around till you are at top dead center #1 cylinder. That means both valves will be shut on #1, and the mark on the balancer will be at the pointer (there are two spots for this, get the right one).

Once you are at #1 TDC, loosen the bolts holding the rocker arms down for #1 cylinder. Then while grabbing the pushrod with your fingers, push it up and down by hand while slowly tightening the rocker bolt down. As soon as you just get the play out of the pushrod stop. Look at your ratchet on the bolt, and count the turns it takes to tighten the rocker bolt all the way down.

1/4 turn is barely enough

1/2 turn is just right

3/4 turn will do

1 turn is getting iffy but will probably work.

Over 1 1/4 turn is too much, and the valve is hanging open all the time.

Then do this for the other pushrod/rocker for cylinder #1. See what you get. Since you got zero compression on #1, if this is the problem it should show up on this cylinder.

 

If I had to bet money on it, i think you nailed the problem. I’ll try that and report back

 

I asked my machine shop guy and he said use the old push rods

 

The machine shop guy is supposed to get it right, but the wild card sometimes is a aftermarket camshaft. But it looks like cylinder #7 is ok, which is unusual.

 

Another quick check on the pushrods:

Remove the valve covers. If a valve is supposed to be closed, try spinning that pushrod between your thumb and finger. If the pushrod has any tension on it, you won’t be able to spin it. This means the valve is not fully closed.

For comparison, try it on the one cylinder that did have good compression. You may have to turn the crankshaft to get those valves in the proper position.

 

that was the problem. Now my truck is running, thanks so much

 

I have to ask, how did you fix it? The solution is usually not very easy or cheap.

 

X2
Dave ----

 

I didn’t tighten my rocker arms as much when resetting the valve lash

 

I thought they where not adjustable you had to tighten them down to a TQ setting?
If left loose they can back off more and drop a push rod.
Dave ----

 

Since he didn't specify what engine exactly I just looked at his profile. There he lists a 1983. And since pedestal rockers started in, I believe, 1983, I, we, figured that's what he had. Apparently, he may have the older ball type.

 

If we are talking v8's, the sled system started in 1978. The sixes may have had the pedestal a little further on, but they still need to be tightened down all the way even on those.

To the original thread starter; I think you will be revisiting this problem after a month or so of running the engine.