Morris Minor Owners Club

Having the opportunity to compare the 1098cc rear engine plate with the 1275cc rear engine plate I thought I would post some photos of the differences especially around the rear main bearing cap.
The 1275cc rear main bearing cap is larger than the 1098cc rear main bearing cap so when fitting the 1098cc rear engine plate to a 1275cc engine some relieving work has to be done to the 1098cc rear engine plate to enable it to fit the onto the rear of the 1275cc engine.
The main problem is the lack of metal in the 1098cc rear engine plate between the hole for the 1098cc oil pump cover and the enlarged hole for the 1275cc rear main.
The pump cover is of a larger diameter (93mm) on the 1275cc engine than the one fitted to the 1098cc engine (89.2mm) and the cover hole centres are set slightly different even though the 1098cc/1275cc camshaft and crankshaft centres remain the same (see photo below).
Whilst it can be made to fit great care needs to be taken so as not to remove too much metal between the 1098cc oil pump hole and the 1098cc rear main bearing cap hole. Therefore it may be beneficial to remove a little metal from the 1275cc rear main bearing top cover to compensate. Too much metal removed from the rear engine plate can lead to cracking between the oil pump and rear main bearing cap holes which is a persistent problem on the 1275cc especially the 1275cc Midget.
The 1098cc rear engine plate has been placed underneath the 1275cc rear engine plate for comparison purposes in the photos below.
As the oil pump covers are also of different diameters the 1275cc oil pump can be a tight fit under the 1098cc oil pump cover.[frame][/frame][frame][/frame][frame][/frame][frame][/frame]

Really helpful and informative article, well done Phil.

I just 'eased' the backplate with my angle grinder till it could be slipped over the rear main. No need to touch the oil pump cover - just use the 'steel backed' oil pump - it's supposedly 'the best' anyway....... You also need to 'ease' the top centre dowel pin hole to fit the slightly larger 1275 dowel pin.

The 1098cc rear engine plate can be eased/relieved to fit over the rear main but it leaves very little metal between the oil pump cover hole and the rear main bearing hole and that is why I suggested removing some metal from the rear main bearing top cover to compensate so leaving a greater mass of metal between the holes so reducing the possibility of cracking. I have had two standard 1275cc Midget rear engine plates crack between the holes and the cracking between the two holes is a widely reported occurrence. So with less metal the chances of cracking of the eased/relieved 1098cc rear engine plate are increased.
Yes the steel backed pump will fit but it still is a tight fit as I mentioned above.

I did consider including a reference to the rear engine plate top dowel/dowel hole but as there appears to be at least three different dowels used for locating the rear engine plate on the 1275cc engine I did not include the references but here is the information:-

The 1098cc rear engine plate top dowel hole is 11/32" dia which is the same as the 1275cc Marina.
The 1275cc MG Midget/Sprite rear engine plate top dowel is 3/8" dia (Pt No: 12G422 (MOSS)) (application - 12cc/Da/H to (e) 12V778F).
There does seem to be different MG Midget/Sprite 1275cc rear engine plate top dowels as the MG Midget 1275cc rear engine plate (Pt No: AEG552 (MOSS)) in the photos above has the 11/32" dowel hole. I have spare dowels for the 1275cc Midget/Sprite engine which are 3/8" dia and 3/8" stepped to 11/32" dia. So some discretion has to be used when referring to the rear engine plate top dowel.
The Marina rear engine plate top dowel protrudes much more from the block than the 1098cc rear engine dowel because of the extra thickness of the Marina cast iron bell housing.
Strangely MOSS give the same part number 12G422 for the 1098cc and 1275cc rear engine plate top dowel !