Not that it is any consolation to you, but one explanation that occurs to
me is that there was a ridge around the top of the cylinder wall due to
wear (as is typical), worn in through long periods of low RPM operation.
Your more aggressive style (although not in itself inappropriate)
resulted in higher piston speeds, which, combined with bearing wear and
thermal expansion, allowed the top ring to contact this ridge with
increasing force, until it eventually snapped. I believe this phenomenon
is not uncommon under these circumstances. It is for similar reasons that
one is advised to "break in a motor in the manner in which you intend to
drive it". Not your fault that the PO was a wimp, of course. But if you
accept my explanation (and inspection bears it out), it would behoove you
to hone or rebore all the cylinders (at the very least), or risk
repeating the experience. Now, it seems, you have an opportunity to break
in a motor properly. Good luck with it.
Anne and Richard Spurling had this to say:
>And the interesting question is: What caused the loss off compression?
>IT WAS NOT MY DRIVING!!!!!!!!!
>Well, actually, it probably was, even though she wasn't getting thrashed.
>The current theory (bearing in mind we haven't opened her up to see) is that
>the DPO just puttered around - I know that for a fact, and that the DPO
>commuted every day into the city. The engine was well and truly carboned up.
>After a week of my ownership, the engine was running a lot smoother, revving
>better and idling better - obviously I drove the car a bit harder and
>cleaned it out. The suspicion is that the new oil, plus a vigorous drive,
>cleaned her out good an proper and something has let go.
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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