You will get alot of advise on this one I am sure, as there are many
opinions on it.
The lip on the top should be removed with a ridge cutting tool. Honing does
not remove very much material and is really only used to break the glaze and
score the surface of the bore.
If you can see and feel the ridge (about 1/2 mm high) it is a candidate for
reboring. The machine shop can look up the dimensions, but I believe the
workshop manual has the dimensions.
Technically you don't have to rebore an engine as new rings will improve
sealing all by them selves. But if you want maximum power you have to
rebore if there is any kind of ridge.
That said I have rebuilt a couple of MG engines and if the compression was
good before I took the engine apart, I just knocked the ridge off, and honed
it in, and bought new rings. This is usually considered part of "freshining
up" the engine, NOT A REBUILD in my opinion.
The ridge is what breaks the rings, and might have been what the previous
owner did....also if you slagged a piston..you should probably take the
block into the machine shop anyway and have it checked over for flatness
cracks etc (though these blocks are VERY tough).
There are many different opinions on engine rebuilds. I prefer safe,cheap,
freshening with most labor being my own.
Good luck with it.
Drew
68 MGB in need of a complete rebuild
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