Anyone know what size bolts the rocker arm pivot bolts are? I am trying to order shims so that I can adjust my valves properly but I cannot find out what size I need. I haven't pulled it all apart yet, was curious if anyone knew off hand. Thanks.

 

They are .312-18 X 1.25, flange head, grade 8.

Tell us more about adjusting your valves using shims.

 

Thank you!

If you do any significant work to your 4.0, you should check your valve adjustment. I built a 4.8L stroker out of mine, used all new lifters, pushrods, rockers, pivots, etc.... The cam is also new along with the majority of the interior of the engine. I had my head resurfaced which removed a bit of material from the bottom side of the head. This causes the pushrods to essentially be longer than before (not actually longer, but the rockers are now closer to the camshaft). This in effect causes the valves to be open longer because they are unable to close completely due to the change in distance between the rocker and the camshaft lobes. In order to adjust them you can place shims underneath the rocker pivots, and on top of the pivot pedestal on the head. This will increase the distance between the rocker and the camshaft lobes. This can also be achieved by getting custom length pushrods. The problem is that I do not know the exact length of pushrod that I would need in order to have my valve preload exact. If you want more detail, let me know I can go into it if you want. Thats the quick and dirty version.

 

Just curious - but wouldn't that imply that the thickness of the shims you install match the amount of material removed when the head was resurfaced? If you went over, the valves wouldn't open enough, right?

 

I've seen special pushrods for determining required length. The end is adjustable, so you just run the end out until you get the lash you're looking for then measure the length of the pushrod tool.

I can't remember where I saw them. Might have been Elgin.

 

Theoretically, yes they should match. It's basically a trial and error fitting procedure, I want to make sure they are exact. I will have to look for the adjustable length pushrods, that's a good idea.