Z1OwnersClub GB

Ok gents, some may know I've been restoring my 650 which I bought new in 77.
It's all finished bar 1 issue which I can't quite get my head around. It seems to be burning oil from no1 cylinder judging from the amount of exhaust smoke, but it runs as sweet as and colour tunes on all 4 to a nice blue burn.
If I take the plug cap off no1 with it running the smoke stops. 2 on its own doesn't smoke at all, nor does 3 & 4.
It'll tick over steady and even at 500 rpm.
Compression is fine and should be 170 psi.
no1 is 180 psi,
no2 is 165 psi,
no3 is 165 psi,
no4 is 190psi.
Valves have been now been re seated, new valve guide oil seals, valve guides checked, bores and rings measure up fine so I don't think it needs a re bore. Good compression seems to confirm this.
After the initial restoration I did about 50 odd miles on it as a shake down. It was smoking then. At that point I striped the top end and did the valves, seals and checked the guides and bores/rings. There was no sign of head gasket leaking oil. I thought after 30 years of non use it would need a little time to re settle but the smoking from no 1 hasn't reduced.
There was oil in the header from no 1 and in 1/2 tail pipe. No 2 header was clean.
Could it be that latent oil still burning off in no 1 header and tail pipe from the now clean exhaust gases or have I missed something?
TBH its fingers crossed it is this latent oil in the exhaust but it doesn't seem to diminish at all and no2 running alone would still cause smoke if that was the case surely?
Suggestions welcome!

Rings wrong way up?

Possibly, but it would be pretty ironic having had the rings off to check the bores/ring clearance that I managed to re assemble it and get exactly the same cylinder to do exactly the same thing.
This has really got me stumped.

May have a crack in the bore/head which only opens up under combustion forces

30 years of non use? was there any water marks/ pitting in the bore? personally i would have fitted a new set of rings if its been standing that long

It had oil in the bores and was turned over every couple of months. Bores and rings look fine although having checked every other obvious possibility it may come to new rings.
smoke is evident from almost initial starting. I would expect a crack to show itself more evidently when warm?

have you looked a the back of the valves to see if its coming from the valve guide or seal ?

Back of the valves was dry and oil free when I took them out to re seat them. Did new valve seals at the same time.
I have a spare engine and was thinking I could swop the head over and see what happens. If it still does it it must be cylinder / ring related. If not, it must be head related.

if the back of the valves are dry your problem must be the bore or the rings. did you use pattern oil seals?

They were pattern seals, however the ones i replaced were oem, albeit 40 yo. No1 smoked with them 2,3 & 4 didn,t. After replacement with pattern seals 1 smoked 2,3 & 4 still didn't.
the bit i don't get is that 2 &3 have lower compression but don't smoke.

how many miles has the motor done?

18k

i presume you put the rings in the bore & measured the gap? & place the rings on a flat surface & measure the gap without any tension ?

I did and all was good according to spec and if there was an issue there I wouldn't be getting 180 psi compression surely?