Hi,
The MGB bulletin board (Paul Kile) provided me with this info.
First type, used on the first 1000 or so MGAs, no timing chain tensioner on
these engines, so the cover looked like a larger version of the Midget
A-series timing cover. Won't interchange with any other MGA or MGB cover.
Second type, used on all but the last 2000 or so MGAs, These had a chain
tensioner bulge in the cover, used an awful felt type oil seal, had three
timing pointers (long pointer is 0 deg. [TDC], the others are 5 and 10 deg.
BTDC).
Third type, used on the last 2000 MGAs and MGBs up through the 3 main
bearing engines, these had three pointers also, but used a better rubber lip
type oil seal instead of the felt seal, fully interchangeable with the
second type.
Fourth type, used on 5 main bearing MGBs up to the 18V engine in 1972, these
had 4 pointers (long pointer is 0 deg, the rest are 5, 10, and 15 deg BTDC).
Interchangeable with the second and third types. This is what you have on
your MGA.
Fifth type, used on 18V engines 1972 through 1980. This had 5 timing marks
(0 deg., 5, 10, 15, and 20 deg. BTDC), the marks were relocated to the top
of the cover so they can be seen from above. This cover must be used with
the late style front pulley, otherwise the timing marks will not line up
under strobe light. Hope this helps, Paul Kile
/Steve Foster Guildford UK.
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