Morris Minor Owners Club

Haven’t posted on here for a long, long time mainly because I can normally find all the answers I need by searching without logging on.

Following an ongoing oily exhaust and a blown head gasket I’ve just removed and stripped for rebuild what I thought was the standard sized 948 engine from my 1959 convertible.

The engine has 950 cast into the block and a nameplate showing it is a BMC replacement with a number starting 8G9 which makes me think it is a Gold Seal.

However, having taken it to bits it seems it is not quite as standard as I thought. The pistons have a reference 20773 B cast inside them which when I search suggests Mini 998 pistons. The tops of the pistons are stamped S47 0.762 which I assume refers to mm and means they are 30 thou oversized although would be great if someone could confirm this.

Will it be ok to keep the standard unleaded head ref 2A629 with these larger pistons or would a different head be a better combination?

I’ve also attached a few photos of the bores, pistons shafts and bearings.

Running a nail down the bores I can’t detect any ridges, but does it look like I can get away with just new rings?

Lastly, any comments on the usability of the other components would also be appreciated.

Many thanks

The engine is indeed not standard 948cc.
It has fully floating gudgen pins, pistons and conrods which means that it has been fitted with 998cc/1098cc con rods. The 948cc conrods have a pinch bolt.
Therefore the engine has in all probability been over bored to 998cc plus.

The camshaft for a 948cc engine should have 3/8" wide lodes. The camshaft lobes in your photo appear to be 1/2" wide. If that is the case the camshaft is from a later 'A' Series.

The 2A629 unleaded head will be perfectly acceptable and serviceable on an engine bored to 998cc plus but a 12G202 head (preferably with a 0.020" skim) would give a bit more breathing ability.

The bores look to be good but I would replace the big end and main bearings as a matter of course provided you cannot when running your nail over the bearings feel deep grooving.

Many thanks for your reply.

I’ve just had a quick measure of the cam lobes and they are 3/8” wide.

Appreciate the info on the bearings, yes there is some scoring so will change, and on the head, having a quick look seems like there are a few on eBay.

Good that it looks like a rebore is not needed. Should I hone the bores when fitting the new rings?

I’ve used a similar tool to this to take the glaze from the bores, the flap wheels don’t want to be too tight a fit, as the flaps are thrown out in use, move the tool up and down a few times and check. You can get a lighter version than the type shown, which might be preferable..

Looks good, many thanks. I measured the bores as something over 65 mm dia so a 50-60 mm version of these with a fine grit will hopefully do the job.