The head gasket burned out between #5 &6 cylinders on my '73 block. The
spec in my (GT6) Bentley manual states that the head and block mating
surfaces to be flat with .004 inches. The head appeared to be flat
within .0015 along the axis of the head and I did not think of checking
it perpendicular to the length of the head - I dropped the head off for
resurfacing even though it appeared well within spec. For $35 I figured
it was cheap insurance. On the block I am seeing about .0015 to .002 in
the very narrow land between the #5 & 6 bores (this is a block with the
recessed lands) and just under .0015 between #3&4 cylinders. On the
block I also checked crossways and I am seeing about the same
clearance. My narrowest feeler gage is 0.0015. I noticed that if I
turned the straight edge slightly of perpendicular to the crank axis
(such that the straight edge is not directly over the head stud holes
that .0015 feeler gage is too snug to move. I suspect that the block has
yielded ever so slightly around the head studs.
So is it time to have the block resurfaced? It is well with in the
0.004 inch spec. THe engine only has 60,000 miles on it since I did a
full rebuild (except having the block decked). There is no other
apparent reason for the head gasket to burn thru ( I did significantly
over heat and boiled out the coolant while stuck in traffic during the
engine break-in 12 years ago - there did not appear to be any problems
relating to the overheating in the past twelve years) There should be no
reason to do anything to the bottom end. I do not look forward to
pulling the engine - on the other hand I am going to replace the cam
since several of the lifters were significantly pitted. One other thing
- the engine is already at 9.35 to 1 comp ratio and now with the head
getting skimmed and possibly the block also the comp ratio will climb a
bit and I would rather have it down at about 9.0 to 1.
WHat do you all think - will I just be replacing one small clearance
tolerance with a similar machining tolerance. Back off to digest mode
awaiting your responses - TIA.
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