Unanswerable question?
 

A friend of mine suddenly had a bad misfire on his 2 year old 454, hydraulic cam, about 400hp. But it still idled fine. Backfired badly when at higher rpm or with load.
Taking off the valve covers revealed #8 exhaust rocker was loose by about 1/4"!!! Exhaust valve height, retainer, and spring were all normal. Rocker arm and stud looked normal, including their installed height. Turning engine over by hand revealed tha cam still lifted the pushrod to specs and pushrod was not damaged.
My diagnosis, a collapsed lifter. But the owner insisted on readjusting the rocker arm and running it. After a few minutes of misfiring while running, took it apart again. Found a collapsed lifter with a badly damaged bottom. So I'm assumuing the cam is damaged as well.
Now the question. Was the cam and bottom of lifter damaged before the valve was readjusted or were they damaged due to running the engine with the lifter collapsed and the valve readjusted?
Gary

Sounds to me like a collapsed lifter then re adjustment was to tight and caused the cam lobe to wipe. If it were on initial start up I would say the cam lobe wiped first. It is possible the collapsed lifter did some lobe damage then when it was adjusted it started galling due to increased pressure. Hard telling!!!!

I have had this problem, the damage was probably done before the adjustments, the rocker arm was loose becasue there wasnt enough cam loeb and lifter left to take up the slack in the rocker arm and valve spring. When it happened to me the lifter foot was so badly worn that it had to be dropped out from the bottom:rolleyes:

I will take the other side of this. I say cam lobe was being wiped out when you first noticed problem. Since gallding had already started, readjusting just continued the distruction of the cam lobe & lifter bottom.

I usually suspect the cam to fail befor the lifter too. But the lift was normal before the rocker readjustment. A 1/4" loosening when closed would have almost certainly whiped that lobe out completely.
BTW, the only reason I'm asking is so I can say "told you so" when we go fix it tomorrow.
Gary

Re: Unanswerable question?
 

If you checked the oil,before the adjust you might have seen metal in the oil?Since you took off the valve covers to adjust I think you would see metal.I agree it happened after.