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Sunday with Sarah

To: british-cars@Alliant.COM
Subject: Sunday with Sarah
From: mit-eddie!wsl.dec.com!kent@EDDIE.MIT.EDU
Date: Mon, 30 Apr 90 10:16:56 PDT
[This got kind of long, but there are some questions at the end...]

I'd made arrangement with my friend with the machine shop to spend
Sunday replacing Sarah's rocker arm and rocker bushings. So we did.
He'd never done the work before, but we talked it over and decided it
was fairly straightforward. The only thing I could remember hearing
about it was mjb saying it was a fairly tedious job for the home machinist.

Well, it wasn't too bad. The hardest part about disassembly was getting
the end caps off. A third of the old bushings came out with finger
pressure or less. Most were worn to the point of showing steel instead
of brass bearing material at the bottom -- several were worn through
completely. (I knew all this because I'd had the rocker assembly off
before to investigate valve train noise.) 

What really surprised me was the degree of damage to the shaft itself.
Every rocker had worn a wide groove into the appropriate area of the
shaft -- and the contact area with the four pedestals was also worn! I
don't understand this latter part at all -- nothing rotates here.

Anyway, we turned a small jig to support the new bushings while
pressing them in. That went quite well, except that one bushing went in
*too* easily. I knew it would be trouble, and it was.

After pressing the bushings in, they needed to be reamed to fit. The
rocker shaft is .0015" under .625, so the theory is that you ream with
a .625 (5/8) reamer and everything fits just peachy. Except that Dave
doesn't have a reamer that big. He did have an adjustable reamer, which
would get up to about .620. So we stuck it in the lathe and modified
the limit stop a bit so it just got to .625. Now came the laborious
part -- took about an hour to take small bites by hand and ream all
eight rockers. As I finished reaming, Dave took a hand grinder and
ground the tips smooth (but radiused) and polished them. 

Then there was that one bushing that went in too easily. There was so
little resistance that the reamer turned the bushing instead of cutting
it. We puzzled over this for a while, thinking about glue and other
nonsense. I finally reamed the one that fit properly, drifted it out,
swapped the two, and remed again. Getting the final cuts in to line up
straight was a pain, but finally... 

Reassembly. Lots of Marvel Magical Mysery Oil. Set the gaps (ouch, my
back), crank for oil pressure, start. No clanks, no valves flying
through the rocker cover. In fact, it's even a little quieter! Let it
idle for about a half hour. Everything seems fine. I'm pretending to
break it in (revs under 3K) for a day or two, and I figure I'll reset
the gaps in a week or so. And keep an eye out for new or good used
rockers, since these all really want to be replaced...

Late last night, I finally figured out why the bushings were all worn
so badly at the bottom, but not at the top. This isn't really a fully
rotating part, and the only force is at the bottom pushing up! Duh. 

Anyone care to hazard a guess as to how many miles this should last? Is
this typically a 'rebuild-only' sort of repair, or should I check again
in 30K miles (if I don't tear the engine down before then)?

chris


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