Original Message -----
From: "Charles & Peggy Robinson" <ccrobins@ktc.com>
HI Don,
No matter what oil you use, a ridge will develop at the top of the
cylinder over time. That's because the rings don't travel all the way
to the top. The point of maximum wear is at the top of the ring travel
because that's where the top compression ring is when the max cylinder
pressure from firing occurs. It's the pressure of the expanding gases
in the cylinder that forces the compression rings against the cylinder
walls to seal the cylinder during the firing stroke. The pressure is
greatest at or near the top of the rings' travel and decreases as the
piston travels downwards. So there's more friction at the top of the
ring's travel. The ridge is actually an unworn area of the cylinder at
the top. The rings may break against the metal ridge on a an extremely
worn engine (I've had it happen) but the varnish isn't in the ring's
travel area.
Cheers,
CR
****************************
Charles (and anyone else),
I recalled an article in "North American Classic" (Issue 13, Page 23) where
the author discussed an R&R on a cylinder head on a '62 MGB. In his
article, he stated (rather emphatically in bold letters) that one should
not remove the carbon ridge from the top of the cylinders. Given the
current discussion on this ridge being responsible for breaking rings, why
would the author advise against removing it?
I just completed a minor rebuild on my B motor and did use a ridge reamer to
remove the ridge as I was installing new rings. In cases where the pistons
are not coming out, what are the current feelings about removing this ridge
and why?
Larry Daniels
79 MGB LE
72 Midget
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