Help needed with valve adjustment

[TheShastStang]

Okay, to start off I am ready to put the finishing touches on a head gasket replacement on a 1989 Ford Mustang LX. My question pertains to the valve adjustment procedure, i am quite curious as to the results that I have obtained. Here is a basic layout of what i have already done.

- Rockers, pushrods, lifters, etc all in place and checked to make sure that they work. Lifters were pumped up, pushrods in correctly, rockers in place.

I did the sequence correctly (rocker on lowest point, zero lash then 1/4 to 3/4 turn, etc.)

So here is my concern/question

When we initially tightened the rockers, we tightened them 1/2 turn past zero lash and performed a compression test to check and see if we had compression before moving on. Only two of the 8 cylinders had compression, and it was not good compression (>50psi). We tried adjusting to 3/4 turn, and that did not help, still no compression. We adjusted to 1/4 turn, and BAM! 120-150psi of compression on all cylinders. However, with only 1/4 turn on the rocker bolts after zero lash, I am still able to turn the pushrod with my fingers. But any further tightening causes the valve to hang open and all compression is lost.

The valves were all checked prior to installation of the heads, the lifters, the rockers, etc. Everything is within spec and (presumably) operating as should. Should I be concerned? Is this a normal issue, or is something seriously wrong that needs my attention before continuing? I have left the valve covers off for now, since I am nervous to continue the build without a second or third opinion from an experienced 'Stanger.

Engine is the 5.0 V8, 5 speed transmission.

Thanks in advance for all of your helpful comments!

 

[TheShastStang]

P.S. all bolt holes were tapped and cleaned before installation of rockers, and all rocker bolts were cleaned with a die before use.

 

[jrichker]

If the heads were milled or a thinner head gasket was used, you could have the indicated symptoms. The answer is to add shims underneath the rocker pedestal.

Here's Michael Yount's proceedure that will get you set up correctly...

Michael Yount’s valve adjustment procedure

Here's an easy way to determine this. Start with the #1 cylinder. Rotate the engine with a ratchet on the crank bolt clockwise. Watch the #1 pushrods. First the exhaust pushrod will rise and fall signaling what would be the exhaust valve opening and closing if the rocker were on. As it closes the intake pushrod will rise -- keep rotating clockwise until the intake pushrod falls and is level with the exhaust pushrod - both at the same height. Both lifters are now on the base circle of the cam - both valves would be closed if the rockers were on.

Now, install both rockers. Tighten the bolts with one hand while rocking the rocker with the other hand - continue until you reach the point where you can't 'rock' the rocker any more because there's no gap on the valve stem end or the pushrod end. You are at zero lash - i.e. - no gaps. Stop tightening just as you reach this point.

Now, put your torque wrench on the bolt and tighten it to 18-20 ft-lbs while counting the number of turns it takes to reach the torque. You should hit the torque within 1/4 to 1 turn of the bolt. If it takes more than 1 turn, use a shim to raise the rocker -- each .030" shim will reduce the number of turns to torque by about 1/4 turn. If you reach the torque in less than a 1/4 turn, or you have trouble reaching zero lash even at full torque, then you'll either need longer pushrods, or to CAREFULLY remove some material from the bottom of the rocker fulcrum. Using the procedure described above, you will work through the remaining 7 pairs of rockers. If you follow the firing order, it will minimize the manual cranking you have to do to get the lifters on the base circle of the cam prior to installation of the next pair.

When I first went through mine, 13 of them took no shims; 3 of them took 1 .030" shim. Upon cranking it up, one or two of them sounded a bit noisier than I thought was right, so with the engine hot, I pulled the upper off, and the valve covers, and went through the installation procedure again. That time, 11 of them took no shims; 4 of them took one .030", and one of them took one .060" shim. And they were very quiet running.

Good luck with it.
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Michael Yount - K'ville,TN 82 Volvo 242w/5.0L; 2000 Suzuki Bandit 1200