O Series evolution

[Wild Bill]

Curious about the subtle changes made to the O series engine. I believe the very early ones were stamped 20HA. Old style rocker, alternator at the back and oil filter at the front.

Mine was built late 1985 and has the old style rocker but the alternator at the front and oil filter below. 20HC42.

I know someone with a 20HC43AA engine and that has the new rocker with an ARG badge.

Does anyone know the date and spec of 20HB engine?

What changes did the later engines also have?

[Jeff Turbo]

O series started in MGB's then progressed to, Marina's, Princess/Ambassadors. Early montego engines had the alternator at the rear, stupid idea, but that progressed to the front 1984/85. Engine was revised with different water pump, oil pump, head, cambelt tensioner etc 1985/88. That wasn't changed until revised when they moved the oil way to the head and moved the sump breather to the rear.1988/89
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