The engine in my B might have lasted a bit longer after I did the
valve job if I'd reamed the ridges out before I put the head back on.
OTOH, maybe not. When I got the car (69 B) it had been putt-putted
around town for many years, never taken on the road. I tuned it up,
took it on the road and promptly blew the head gasket. So after I had
the head trued and a valve job, I drove it for a year or so until it
broke a few rings while on the freeway at 70 mph. I wasn't really
surprised because I knew it had a lot of wear in the cylinder bores.
BUT, did the rings break because the top rings came into contact with
the ridges because I drove it hard or did they just fatigue and break
because they were cocking and flexing in worn grooves in the pistons?
No way to tell. The lower compression rings were broken too. The only
original parts in the block now are the rods, crank, and dizzy/oil pump
drive gears.
I do know that one reamed the ridges out when new rings were to be
installed, so as to prevent ring breakage. One guy I worked with always
reamed them out unless they were to be rebored. Probably a good idea if
you run a shop and want to be sure. I sure can't see where it would do
any harm. Maybe Lawrie has some thoughts on the matter.
Cheers,
CR
Larry Daniels wrote:
> 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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