I got a lot of responses on this, so here is a quick description of the
procedure for those who can't wait for the photos:
Tools needed: Electric drill and 1/8" bit, pop rivet gun and small pop
rivet, Small box wrenches, nut drivers, or pliers for removing the
cable, needle nose pliers for removing the valve cap pin.
1. Go to your FLHS (favorite local hardware store) and buy 5 or 6 #4
washers (about 3/16" diameter), preferably in stainless steel. Drain
cooling system from radiator petcock (save and reuse if it is less than
two years old, otherwise this is a good time to flush and refill with
modern orange long life coolant).
2. Remove the cable, and mark the position of the top of the valve in
relation to the cast aluminum base with paint or crayon. This is where
the folded over tabs are.
3. Drill out the pop rivet below the cable holder and twist the valve
body off the base. The rubber diaphragm might separate from the valve
mechanism and stick to the valve base. If it does, gently pry it off
with a small screw driver.
4. Inspect the rubber diaphragm. If it came off the mechanism, work it
back on over the flange. If the rubber is too hard to do this, or
cracked from age, buy a new valve and go back to step 3. Those of you
who have very old valves or don't know the condition of your valve may
just want to get a new one and modify it rather than risking laying up
the car for a week or so waiting for a new valve.
5. You will find that the valve closing is accomplished by a small cap
with a spring under it that is held in place by a hairpin type pin.
This is the problem, the cup is positioned way too far forward and
closes off the valve too early in the stroke of the mechanism.
6. Remove the pin (don't lose it, it's tiny!) and install enough washers
on top of the cap to just leave 1/16" of spring compression under the
cap and replace the pin. This took five in my case. Test that the cap
still contacts its seat by holding the assembled valve onto the base
with the valve mechanism closed. Note that there should be a slight
compression effort felt as you press the valve onto the base when the
valve is in the closed position, if not remove a washer and try again.
Both of the reasonably new valves I did were identical in needing five
washers, so this will probably work for most folks. If you want to be
absolutely sure the valve closes completely, you will have to remove the
base from the head and blow through the assembled valve to test it,
which is what I did with one of mine.
7. Re assemble the valve noting your positioning marks and install the
pop rivet. Be sure that the rivet goes in the hole that is centered on
one of the ears on the base so it can't rotate in any direction. No
sealant is necessary for a valve with a good rubber diaphragm.
8. Hook up the cable, test for proper range of motion, refill the
cooling system and enjoy the new found heat!
If you don't get significantly more heat, it's time for a new heater
core!
Have fun!
--
Stuart MacMillan
Seattle
'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)
Assisting on Restoration (and spending OPM):
'72 MGB GT (Daughter's)
'64 MGB (Son's)
Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT
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