BEFORE I TEAR DOWN, your .02 please
 

Never have problems until. Fresh oil change, 80# been running about 5000 for 5-8 min 165 temp and it studdard for just a second
and back klean so I slowed to idle and pressure is about 20, (normal hot idle is 40+) and I can hear what sounds like cam slapping lifter. Oil pressure off idle was still 80#.
After cool down I pulled plugs, all look fine, pulled
rocker covers (quick) inspect nothing bent or tight. Oil level is fine
and clean. With covers off, refire and noise is there, oil pressure @ idle was again @ 80#, when running at higher RPM sound is not so loud and no miss it runs smooth and clean. I will be pulling covers off again tonight for closer inspect on valves and adjustment and working my way down from there. Please let me know your thoughts.:(
GEO

Blown lifter, broken inner valve spring, bent push rod or pulled rocker stud. My .02

Good luck,

BT :cool:

Kill each cyl and see if it goes away. If not it may be a spun cam bearing causing loss of pressure at the lifters.

What you may have done is partially melted a piston and it is hitting the head. Is the tapping sound 1/2 engine speed like a loose lifter or full engine speed. To test this loosen a lifter and see if it is at the same speed. IF it is then it is a valve train problem. If it is full engine speed then it may be a melted piston ( valve flycut eyebrow) or a bad bearing. Running any high performance engine at close to WOT for 5 to 8 minutes is asking for problems.

Tinker, good call
 

#3 broken above ring land on upper side. Looks as if blew
head gasket between 3 and 5 shortly before it came apart,
hasn't been that way very long you can tell. Checking bearings
now it seems all pieces went out the exhaust except 1/4" x 1/16
melted to head. I feel very lucky this time.
While it's apart I will be doing this winters valve train rebuild,
valves, springs, along with rings/ bearings and 1 new piston.
What is nice about a Paul Pfaff motor is I can call on Mon. to order
a piston, and he can grind to the weight of the others and ship
at days end. Last time I sent rods and pistons I had them back in
my hand less that 10 days balanced, sized and hung on rods, with rings and all bearings. After 18 yrs he still has my build sheet.
GEO