MGB OVERDRIVES: Both the three synchro and four synchro gearboxes
are available as overdrives. However, in each case, there are many parts
required for a conversion besides the overdrive unit -- intermediate
housings, mainshafts, etc. If you want an overdrive gearbox, buy a
complete unit. I have several, in fact, rebuilt. The earlier 4 synchro OD
has a top fill, just as the complementary non OD gearboxes; the later (74/2
->) have a side fill. Both require 20W50 ENGINE OIL! The former drives
the speedo at 1280 turns per mile; the latter at 1000 tpm. This number is
also indicated on the bottom RH face of the speedo.
EVAPORATIVE LOSS CONTROL - ELC - 77B: Fresh air enters the large
black hose at the radiator diaphragm, travels through the anti run-on
valve, through the charcoal ADsorption canister, into the restricted port
on the valve cover, out of the engine from the front tappet inspection
cover and into the breather on the carburetter. This system was in place
from 1972 -> 1980. It is a good system and nothing is gained by its
removal. As the tube on the front tappet inspection cover is 1/2" and the
brass tube on the carb between 5/16" and 3/8", I simply push a 18" length
of 5/16 hose into an 8" piece of 1/2" hose with help from some silicone
lubricant or some oil. Now it is easily connected!
FITTING FELPRO SEALS to the VALVE GUIDES: Completely loosen ALL
the rockers and remove from the shaft #1 and #8. Remove the plugs. In the
case of the number one cylinder: Rotate the engine so that it is possible
to slide the #2 rocker rearwards, then turn it 90 degrees; feed as much
cotton clothsline into the #1 cylinder as possible; rotate the engine until
that line is squished up against the bottom of the valves; use a pair of
screwdrivers and lever down the top spring plate while your associate picks
out the collets or keepers. Easy!
SLIPPED TIMING CHAIN: Timing chains DO NOT jump teeth. It just
doesn't happen. Check your valve timing: With #7 fully open, set #2 at
0.055". Rotate the engine until the #2 rocker just contacts the #2 valve
stem (use a piece of paper). You will find your timing mark on the front
pulley at TDC.
MGA IGNITION TIMING: The manual asks for 5 to 7 degrees BTDC.
This equals about 20 degrees BTDC at "tickover" which is about 800 rpm.
The micro-adjuster on the distributor allows field testing. Advance until
you can get it to ping -- then back it off so it doesn't. Eleven clicks to
MGA PETROL SENDING UNIT GASKETS: The new and improved rubber
gaskets are only new. They expand and then leak. Original cork gaskets
are to be soaked in oil, then fitted. That's too slow for the shop -- we
use Permatex #2. DO NOT USE SILICONE SEALANTS!!
MGB CYLINDER HEAD CRACKS: ALWAYS fit hardened inserts to AT LEAST
the exhaust seats. The end mill operation removes the tiny cracks.