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Old 08-22-2018, 10:39 AM
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tgreese tgreese is offline
 
Join Date: May 29, 2003
Location: Medford MA USA
Posts: 10,978
Has the 401 been rebuilt? As mentioned, the cylinder walls are thin. The larger 401 bore combined with the existing bore spacing requires that the cylinder walls be thinner than the 304 or 360. These blocks are spec'd for 20-thou overbore maximum, as I recall. If the cylinder wall is too thin next to the cooling passages, heat from combustion travels quickly into the cooling water instead of being carried away with the exhaust gases. If you search, you'll find many instances of 401s bored say, 60-over with hot spots in the bores that made them overheat terribly.
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Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
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