Bore flex occurs in all A-series (even stock) except perhaps the A+, which
I have never had the pleasure to own. A+ blocks have ribbed reinforments
externally like the ribcase trannies. This is the main reason I've deceided
against way oversizing the bores on a rebuild.
Gerard
At 7:24 AM -0400 7/27/01, Robert E. Shlafer wrote:
>Hi, Robert!
>
>I'm on the way out the door for my normal
>airline trip but happen to be on as I found
>a message for "justbrits" (he's mad at me,
>as if you couldn't guess!) which should
>help him understand he made a mistake.
>
>Anyway, Vizard does mention bore flex
>in his book and I think It comes under
>"Big Motors"; don't have this handy right
>now.
>
>I'll have to do this from memory, so I could be a little wrong on this.
>
>Beyond a certain bore (73.5mm+, I think,
>though it may be more), the cylinder walls
>get thin enough to really weaken, especially on thin flange blocks
>(1275's)
>so that at high rpm, the block or walls
>will actually "flex", causing loss of compression and oil control (rings
>no
>longer making proper contact with
>"moving" cylinder walls), along with
>attendant blow-by pressurizing the
>crankcase, of course.
>
>The A+ blocks are supposed to be a lot
>stronger in this respect, over and above
>the thick flange pre-A+ 1275's.
>
>I wish I had the time to find the right page
>but I gotta split.
>
>Hope this helps!
>
>
>
>
>Cap'n. Bob
> '61 :{)
>
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