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NoShortcuts (2/20/2015)
1) Ted mentioned that SOME 312 blocks are found to have cam tunnel bore alignment inaccuracy. Since numerous FoMoCo block casting series (five?) from '56 through '60 were used for either 292 or 312 engine production, is there any speculation as to WHY the cam tunnel bore issue is found in 312 produced blocks and not 292 blocks?
Might the 312 main bearing bores and and cam bearing bores been machined on a particular production machine?
OR
Might the misalignment inaccuracy be tied to block twist (over time) caused by reduced engine block structural integrity brought on by the 312 engine bore being .050 larger than the 292 engine bore?
2) Have the cam tunnel bore issues been found more frequently on some 312 y-block casting series from '56 to '60 than others?
Charlie. For a while the cam tunnel problem looked to be more prominent in the ECZ blocks but then it was also noted in the earlier 312 blocks. Some of the cam tunnel issues arise from the cam tunnel bores not being aligned with each other while other issues arise from the cam bores themselves simply no longer being true in regards to roundness. I suspect the problem stems from the larger main journal sizes on the 312 which takes away from the internal rigidity of the block itself around the main and cam area. I recently performed a build up on a C2AE-C 312 block and in that case the cam tunnels were perfect. That particular block has the reinforced main webbing which may be a key component in allowing the cam tunnels to remain straight and true when the main bore sizing is increased.
  Lorena, Texas (South of Waco)
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