Have had a busy week and to be honest only got to calling Graham this morning. He ran through a few possibilities and after discussing piston fitting process I am quite sure I have stuffed up or damaged the oil ring assembly also as some of you suspected. I will put engine out and inspect oil rings, GR is going to assist me as needed when I get to that point.

Thanks for you help, unfortunately not a simple fix I was hoping for but at least I can get to fixing it now.

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1968 Morris Mini Deluxe - members gallery
1970 Morris Cooper S - members gallery
Mini's I grew up with
Slot car couch

If all four cylinders are burning oil The question is did you break all the oil rings Its a common fact.
Lets see some pictures after the pulldown

Number 4 had some light oil but wasn't to bad, similar with 1. 2 was then the the next worse but 3 was by far the worst.

Combination of me rushing through jobs, to be honest trying to get this Cooper S on the road over last 2 years has been a real strain. At a stage of life where I only really have time to drive them, not work on them.

Added that my ring compressor is rubbish and I had some trouble installing oil rings indicates operator error and doesnt surprise me as the day I attempted fitting them I had to much going on.

Will pull motor out, give to my father who unlike me is a mini guroo from way back and also a gentleman, let him do his thing and owe him another favour!

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1968 Morris Mini Deluxe - members gallery
1970 Morris Cooper S - members gallery
Mini's I grew up with
Slot car couch

Hope it works out well mate, I always get a second pair of hands putting pistons in. I think Docs tapered compressor is a great idea.

Was this issue ever resolved? Were the oil control rings causing the problem?

I'm facing a similar situation: brand new motor, built by professional engine shop using hypatec pistons, Hastings rings, new valve stem seals, etc.

It goes really well, no smoke on start up, idle or acceleration. However, if you nail it then lift off and decelerate (creating maximum vacuum in the bore), there's a big cloud of blue smoke coming out the back.

Maybe it needs more aggressive running in to get the rings to bed in properly. Thinking of throwing a handful of Bon Ami down the carb throat (an old Americano hotrodder trick).

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

I am guessing he sorted car is on carsales

I had the same issue about 10 years ago. I had 2 (TWO) engines done at the same time, and each smoked like hell. Have to add that up to that time I was over quite a few successfull rebuilds with perfect results. I was very determined to find the problem. Took the engine apart at lest 20 times. Realy. Took the shortblock to at least 5 machine shops, finally even to a university. No success. When I finally put seals on the exhaust valves as well, the smoke nearly dissapiered, but not completely.

At the end I removed the shortblocks and had them rebored at another machine shop, and all of a sudden the problem was gone.

Neither me, nor anybody else could tell what was wrong with the first company's work. The bores were round, straight, the honing was done to a good surface standard, gaps, cearances were all in spec. And still.

I have spent about 6 months to solve the problem. It was the worst time of my professional life ever.

Sorry if I cant solve your problem, but maybe... You need to do the same: find another company and get the shortblock done again.