Doug,
This seems like a perfect opportunity to settle a long-running question.
Namely, can you overbore a 260 to 289. I personally would be willing to
pitch in $20 toward the cost of getting your cylinder bores ultra-sonically
tested for thickness. I'm sure there are several Listers out there who would
be willing to bet ten times that amount that it can. I'll be glad to take
those bets. If you play your cards right, maybe you can get your rebuild
paid for. ;-)
You need to carefully measure the bore diameters to see if they are really
at 4.030". Maybe the two that show boring tool marks are still under. You
should also carefully measure each of the pistons. The last time I rebuilt
mine, one out of the eight pistons was 0.007" off. Personally, I don't
believe the overbore/overheat link. If the pistons are installed too tight,
then it will overheat. I had an engine rebuilt once that had just a skoshe
too little piston clearance. It eventually seized up and tore itself apart.
It would do OK as long as the water temperature was under about 200F, but at
higher temperatures, as the pistons expanded the temperature would start
climbing. As I recall, about 0.00035" is about the right clearance, but
check with the specs that come with the pistons. As the saying goes, "Better
to hear it than to smell it."
The good Mr. Laifman has offered the following: "The scientific explanation
is that your mechanic is full of sh--. The 260 block has the same OD of the
cylinder to the water jacket, but a smaller bore, so the walls are THICKER
than a 289. The factory (FORD) recommendations on boring are a maximum or
0.060 inches on the 260, and 0.040 inches on the 289."
There are two distinct schools of thought on this, those that think Steve is
the one "...full of sh--", and those who don't. Amongst the many standing in
opposition to Steve is the following from an "official" Ford FAQ's Website:
"Many 289/302 parts fit earlier 221/260 engines (which had smaller bores).
They also has less metal around the bores, so you cant overbore to come up
with a 289."
Here is the link; I'm sure there are many more that echo this view:
http://www.oemfordparts.com/faq/smallblockv8.htm
I recently bought Mustang & Ford Small Block V8 1962-1969 by Bob Mannel in
the hope of getting a definitive reference to these kind of questions.
Unfortunately, it does not address the subject of block castings in this
detail. One might speculate that the later (1963/1964) three-freeze-plug 260
engines might have been just underbored 289's as Steve seems to suggest.
However, the 260 bore is a full 0.200" less than the 289, so that logic
would dictate that, if you can overbore a 289 by 0.030", then you can
overbore a 260 by a whopping 0.230". Steve's statement that the maximum
overbore for a 260 is only 0.040" would seem to prove the point that the 260
blocks are cast with small cores than are 289's.
As a counterpoint, however, the Mannel book has a number of Ford adds
reproduced throughout the book. One in particular shows a boring bar and a
fist with the admonition "Put away the boring bar-" It then goes on to
introduce the new 289 and makes the statement: "The factory overbore is
better than doing it yourself . . . you know the cores are in the right
place . . ." Taken at face value, this seems to suggest at least the
possibility of overboring to 4". I'm sure this debate will rage on until
someone like you Doug, is willing to take some measurements and help us out
of our quandary.
Bob
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