The MG engineers very thoughtfully provided a damper spring so that
the shifter rod (in the aluminum extension housing) would not rattle
with engine vibration. The cumulative impact of the constant downward
pressure of the plunger and the abrasion of the steel rod across the
aluminum bearing surface is a ditch dug in the bearing surface. In
mine it was about 1/16" deep, with the effect that the arm at the end
of the rod was about 1/8" below the (somewhat) spherical bearing
surface of the shift lever itself.
Abingdon Spares quite thoughtfully provides a sintered bronze (oilite)
bushing insert to alleviate this problem. Unfortunately, they do not
have any good advice with respect to how to install it. The problem
is that the hole is worn eccentrically in the extreme, and simply
drilling or reaming out the existing hole will yield a bigger
hole that is centered on the old worn hole. This will reduce the
rattle but will also leave you with a shifting rod that is grievously
mis-aligned.
One must then enlarge the hole on the original axis. This problem is
exacerbated by the location of the hole, about six inches from the end
of the casting, and its depth, about an inch and a half. The presence
of only one flat surface on this casting is another annoyance.
Most MG list readers have left by now. This is for the Serious
T-series Restorer only....
1. Go to the tool store and get a Milwaukee Model K horizontal mill.
The good news is that they are available for about 50 cents a pound.
The bad news is that they weight about 6000 pounds.
2. Lightly clamp the extension housing on the bed, upside-down, with
the axis of the shift rod roughly parallel with the axis of the mill
arbor.
3. Make a purpose-built (thats Britspeak) cutting tool by turning
down the end of some half-inch steel stock to 7/16 (leaving some room
for chips) and drilling an axial hole (for a setscrew) and a diametric
hole (for the cutting tool). The cutting tool itself is carved out of
a busted tap. Admit it, you always have plenty of those lying
around... This entire assembly needs to be about a foot long.
3. Make an alignment tool of half inch steel rod about 20 inches
long. Clamp it in the Milwaukee arbor and thread the housing
bearings over it.
4. In theory, this should set up the housing with respect to the mill
axis. In practice, it does not, because the bearing holes are worn so
much. Throw out the alignment tool.
5. Go to McDonalds and get lubrication necessary for the machinists
involved.
6. Use a C-clamp to stick a Starrett "Last Word" dial indicator on
the mill arbor. Let the original shift rod lie in the housing
bearings as a guide. (This works on the assumption that _all_ of the
wear is on the bottom surface of the bearings, since the plunger
pushed the rod in that direction. Of course, the bottom surface is
now the top since the housing is sitting on the mill table
upside-down.)
7. Spend about an hour setting the piece up. Use a paperclip to
break into the tool crib because you need some brass shim stock.
8. Spend another half hour setting the piece up because you realize
(just before cutting) that the rear clamps are loose as a goose.
9. Set the first cut up for a half-inch diameter and the take
subsequent cuts of about 0.010". Marvel at the moonscape created by
the chatter from a dull cutting tool on the end of a foot-long stick.
10. Cut the diameter to a total of about 0.600. Center a 5/8" reamer
on the mill arbor and clean out the remaining swarf. Soak the bushing
in oil for 24 hours and press it in.
The finished product slides like grease. But it took about 4 hours.
No, I don't want to do it again.
Yr Faithful Correspondent A. B. Bonds
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