The O Series 

History

Back in the late 70's with the need for ongoing development of the MGB prior to the decision to close Abingdon, work was being done on fitting the then new O Series engine.  This was a departure from the B Series, being a SOHC unit of 1700cc and later 2000cc.    

To quote an article by Roger Parker:

"The first application for the 'O' Series was in the Princess range of saloons where both engine capacities were used giving 78 and 91bhp. Soon after the 78bhp 1.7 engine was slotted into the Marina which replaced the 1.8 single carb B series, but the twin carb MGB spec engine continued for a while. Later still the 2.0 litre engine was used in the Marina, but attached to an auto gearbox. Next to receive the O Series was the Sherpa Van, again with both capacities being used.

The irony of the period was that the car that originally provided the justification for the new engines development, was the last in the list to actually receive it. As we all know the MGB version of the engine was never allowed to reach production, but the actual specification for that engine was developed ready for production. This meant the only MGBs ever to officially receive the 'O' series engine were factory development cars, an number of which found their way into private hands, but without the 'O' Series engines.

There were to be two different specs for the MGB, both 2-litre, one with a classic twin SU carb set up and the other with multi point fuel injection where emission regulation was stricter. The actual carb specification engine was to be the more powerful with 105bhp against the injected versions 100bhp, if documentation I have seen is correct. It certainly would appear to be realistic estimates.

History tells the story of how MG was to be no more, let alone seeing an O series engined MGB. In the first two years of the 1980s the twin carb spec of O Series was to find a home in both the Rover SD1 2000, and the revamped Princess range called Ambassador. Ironically the TR7, which was the "favoured" sports car of the period, was also to have received the O Series engine! .....

.....By 1982 I was into the ninth year of ownership of my MGB and I had built and fitted a 1950cc engine with very many modifications. The effect of all these modifications was significant but perhaps a touch crude. As a result I actually started to look into fitting the 2-litre O series engine, as it could be lifted straight out of the Sherpa van where it was attached to a version of the MGB gearbox. Sourcing a pair of SUs and manifold would not have been difficult and "hey presto" I would have created a replica of what might have been."

The picture below was sent to me by Roger Parker showing a test engine in a development B:

The story is that the O Series development Bs had their engines removed and were sold on, many being fitted with a standard B Series.  However, as Roger states above, ""hey presto" I would have created a replica of what might have been."  To this end, both Stephen Whitham and I are now heading down this road, too, but more on that shortly.

A detailed history of this O-Series engine can be found here at Keith Adam's website. To quote from that link:

"That is not to say that the O-Series was without its merits; only that it was a bit of a "rough diamond" in the early years, offering little advantage over the outgoing B-Series - certainly in terms of performance and refinement. As stated though, it was a good 20kgs lighter than the B-Series engine, and the block was shorter and therefore easier to package. Also, the aluminium cylinder head allowed for unleaded fuel usage... (it is a shame that the O-Series powered MGB never made it)."

The 1700cc O Series looks like this as fitted to the Sherpa:

This particular engine having come from a Sherpa will have a backplate suitable to mount to the existing B gearbox.  The one shown above is a lower powered single carb unit that I have just purchased off Ebay for £10.

As mentioned above, the O Series also found it's way into the Rover SD1, and this is what it looks like:

Note the additional emission equipment on the twin 1 3/4" carbs, as well as the power steering pump on the top front right.  This set-up was purchased off Ebay for £100, although, had we got our act together we could have had it for £50, but that's another story!  The fact it comes with an LT77 box which can be sold on (read Fitting an O1 Series lower down) as well as the fact the engine is from the SD1 and was rebuilt but never used, and is reputedly bored out to 2100cc, I don't think we have done too badly!

Both the engines shown above are now retrospectively known as O1 Series engines as noted by the fact that the distributor is mounted in the centre of the cam.

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