Fitting An O-Series Engine

Roger Parker has written an article in Enjoying MG that covers both O1 and O2 as well as the M and T Series engine aka M16 and T16.  What is of note is the that the article covers two potential options here for the 01 Series. As Stephen and I progress with fitting this to his car we will write more on the details of such a fit.  However, as engine options go, this has to be the cheapest and easiest route away from the B Series really only requiring the right engine and adapting engine mountings to suit, but without the complexities of a gearbox change or hooking up fuel injection.

In effect, there are two choices of gearbox to use with the O1 Series here, either the standard B box with the benefit of Overdrive, or the later 5spd LT77 box.  The latter option adds some complexity to the engine swap, but as the fitment of the LT77 is well documented by the V8 brigade, this should not prove too tough a task.  The simplest route, though, for Stephen, would be to fit the Sherpa backplate to his 2.0L engine and use his gearbox which is a known quantity rather than the unknown LT77. 

Roger's article sums it best:

"The more I have gone into the detail of this option (the engine and standard B gearbox) the more it shows to have been a logical progression for the MGB. The fact that the engine is not the most exciting has probably prevented anyone mimicking the projected factory 'O' series specification. However there is reasonable potential in the cylinder head to have some simple flow mods done, by an expert like Peter Burgess, that should enable the engine to be quite a bit more lively and achieve an extra 10 to 15 bhp. The result would be a very lively MGB and one well able to acquit itself in modern traffic flows. It would be considerably faster than a standard MGB due not just to the extra power but also a much stronger torque band and smoother engine."

As part of the research into this latest project I put several questions to Roger Parker (one of the benefits of being an MGOC member!)

Q. What tuning options do we have?  Does the head benefit from porting?  I was wondering along the lines of an EDIS unit plus possibly fuel injection given the individual inlets. 

A. Yes to both, although the injected versions of the MGB Federal O series were to be rated at 100bhp and the twin carb UK specs at 105bhp, so in tuning terms the good old SUs will provide more than enough airflow to produce the same peak power as the injection system would.  However, injection wins elsewhere in terms of instant starting and running with no messing with choke controls, usually slightly better emissions and sharper throttle response and mid range torque.  Mind, the differences are actually small and SUs look more appropriate in an MGB body.  Head modifications can make quite a difference and I would expect that to be in the order of 15%.  Peter Burgess has done many O series heads and can extract the best for the least work.  Don't bother looking for anything more than his Econotune specs as it really isn't worth the time and money.

Notes from Roger Parker with regard to fitting the O Series engines to an MGB 4spd gearbox:

The saloon flywheel has a huge additional mass over the Sherpa flywheel (or at least those I have experience of are like this) and as such the use of the lighter Sherpa one is beneficial. Diameter of the flywheel has to be checked for clearance against the B series gearbox, but I would expect it to fit. The saloon flywheel presumably comes from an application using the LT77 (SD1 gearbox) and as this was developed for the Rover V8 saloons with a much bigger clutch (9.5") than the B series range of vehicles it has a bigger bellhousing to accommodate both the flywheel and the clutch, hence the suggestion of the Sherpa unit. Throttle response will also be improved with the lighter and small diameter Sherpa unit.

Essentially the clutch release will be a suck it and see, but I expect the Sherpa release arm and (roller) bearing to be needed. It will have no issue with the stronger clutch as the Sherpa used an uprated clutch and I used to use a Commer 2500 van clutch with my uprated MGB engine before the V8 conversion, this was an 8.5" against 8" MGB clutch. That didn't show any problem and was a bolt on change.

Starter is as you expect, matched to the flywheel.

Oil cooler: a 10 row would give more than enough cooling. The earlier O series has the oil filter in a convenient position at 90 degrees to the block and so a spin on adapter is viable for the take off. These can be bought with a stat and that ensures the cooler is only used when the oil is hot enough. If the resulting clearance between adapter and the inner wing is too tight for the filter and a short filter is not viable, then rather than use the stat version take off, use a base take off version and closing end cap and a remote filter and cooler in the same way I did for the M16 engined cars I did and the same as V8s.

Fitting the O2 Series Engines to an MGB

The O2 Series engine is not quite the easy fit of the O1 Series engine but is still possible.  The major modification being the necessary clearance for the oil filter, along with the re-design to a cross-flow head, putting the inlet system on the opposite side. The oil filter problems relate to the later O2 series from 20HB series on and all 16 valve (M/T 16) versions where the filter is relocated and under slung.  On the original O series (O1) engines and 20HA (02) engines the oil filter hangs off the side.   In addition, the distributor moved from its mid-mounted position to a front mount on the O2 Series and later again to the rear of the head on M and T series engines until it was replaced with electronic distributorless ignition in 1995/6.

Below are pictures of Keith Dale's O2 Series conversion using Sherpa power and Rover SD1 LT77 gearbox in a rubber bumper shell!  You can see from the photographs (scanned from Enjoying MG - MGOC magazine, September 2005 and February 2006) that a fair bit of effort went into firstly tuning the engine, and then modifying the bodywork and cross-member to fit it.  

Note the customised inlet manifold, a combination of the B's twin SU with the original single carb manifold.  Also, in this set-up, the distributor has been moved to the front to allow the heater to be retained.

A subsequent upgrade has been the fitment of a modified air-inlet system, and with profiling of the needles and timing the engine gives 101bhp at the rear wheels. Note the ducting to ensure the air passes through the radiator.

These photos below are from Keith Dale's collection:

This one showing the cut for the boxing of the cross-member.

This one showing the engine and cross-member in relation to each other with oil pump.

I have also received an email and some photos from Karsten Mikkelsen in Denmark who is fitting an O2 Series engine.

This photo shows Karsten's modification of the sump pan.