Arnie,
My suggestion would be to ensure that the studs are not pulling out of the
head. Put a straight end along all of the studs. I assume you have a stock
260 head with the correct adjustable rockers that DO NOT have the provision
to align on the valve stem tip. They are flat where the contact the top of
the valve. I would check Valve to piston clearance and valve spring coil
bind. I would also check whether you can fit a .010 feeler gauge between the
coils of the valve spring at max lift. Why it would show up after 300 miles
I have no idea but it sounds as though you will need to recheck everything
to diagnose it. The other option is to just stick in some new pushrods and
away you go. It is also important to ensure that the pushrods are such that
the guide "slots" in the heads are not worn. If they are or if the engine
builder did not ensure that the rockers ride directly over the valve stem
tip it could have widened the slot enough to alter the geometry enough that
the pushrod bound and bent.
Another possibility is that the slot in the rockers is not long enough for
the cam you are using and may bind slightly. Look at the ends of the slot on
the rockers or the stud itself for contact.
Do not rule out a delayed failure as I used to street race my car late at
night and have a great night racing, drive home and then get up the
following day and on the way to work about 40 minutes from home a rocker
would just break half way there due to the bind. I also did it with
pushrods. It may be something similar. Be specific about what your
combination is and perhaps it may give a clue.
The fact that it is 2 intake valves indicates that they may have touched a
piston.
Best Regards,
Tim Ronak
Business Development Manager
Akzo Nobel Coatings
Off: (949) 305-5393
Fx: (949) 305-5394
Cell: (949) 439-4784
email: timothy.ronak@akzonobel.com
VM: (800) 234-6747 ext. 2257#
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