Long story short: I bought my neighbors 86 F150 with a misfire, but I haven't had to much time to devote to fixing it. The intake manifold gasket doesn't look great, so I decided to remove the intake/exhaust manifolds to replace it. The valve cover was leaking a decent bit as well, so I figured I would pop the valve cover off since I had everything out of the way to peak inside and replace the gasket. Well good thing I decided to do that because I found a bent pushrod.

I have the 86 shop manual and have read over the valve clearance and valve tappet sections a few times, but have a few questions:

1.) Is it ill-advised to replace just the bent pushrod and not all 12?

2.) It looks to be a 5/16" diameter x 10.14" push rod. I don't think the engine was ever rebuilt or opened up. Do I need to go through the valve clearance procedure to determine the push rod length or should I order the standard length ones?

3.) The manual mixes torquing the rocker bolts in with the valve clearance check. When tightening the rockers to the required torque, does the engine have to be rotated to a certain position? The procedure talks about the position of the cam, but I am assuming this is linked to step where the lifters are depressed to check the clearance and not the torquing step?

4.) While I have the valve cover off, is there anything else I should look for?

I don't have too much experience with engines, so hopefully these questions make sense. I appreciate the help guys.

Thanks!

 

With bolt down rockers it's pretty easy. You can just replace the bent pushrod, either order a new one or see if you can find one at a local yard.

Remember exhaust open (EO)/(IC) intake close to adjust the lash. If it's the intake valve turn the engine by hand until the exhaust valve rocker starts to open, then torque to spec. If it's the exhaust turn by hand until the intake valve fully opens then starts to close.

 

The first thing I would do is find out why the pushrod bent, if possible. It may have been over-revved or maybe the valve is stuck in the guide, or even bent, or the rocker arm bolt could have loosened up, or the valve spring has broken. MOPAR engines are notorious for pushrods that punch thru stamped rocker arms and subsequently bend - maybe something similar here. Put a lever on the valve or rocker arm and move the valve open and closed about 3/8" by hand. If the valve does not slide in the guide easily and smoothly find out why.

 

I decided on just replacing all 12 pushrods since they are fairly cheap.

I did a decent amount of reading yesterday, but somehow didn't come across the EO/IC method. The shop manual directs to rotate the engine to #1 TDC of compression stroke, tighten both #1 E/I rockers, rotate crank 120 degrees CW, tighten #5 E/I rockers, and then keep rotating 120 degrees and tightening through firing order. Either way, I think both methods accomplish the same thing: tightening the rocker when the lifter is on the base circle of the cam, but it's a matter of when you're catching the valve closed.

Good call. I found a nice thread yesterday with similar advice in terms of finding the cause and unsticking a valve. I think I may pull the plugs and rotate the engine by hand while watching to see if anything appears to be sticking/stuck. As suggested, I'll also try to manually open the valves as I go through.

Help - misfire in Ford 300 six | The H.A.M.B.

I appreciate the help guys. It is definitely a learning experience so far!