Trixie Combat got about 30 miles run in when I changed oil and took TS cover off to get broke points bolt out, to find the cold cam chain rather tense, more than I'd set it too for sure, rolling and checking for all around slack when hot. A bit of blank Brit Iron staring state as never expected to find it tighter. Ain't rolled engine yet to check chain over all tension again but this is weird. Only thing I can conceive is bent shafts that landed chain on the tight offset position, which don't make sense either. Insights accepted. Ok - worked myself up to go out and diddle Trixie till in least pensive road worthy state.

Edited to short cut wasted viewing. All is fine but the mechanic.
I'd forgot I'd left crank near TDC to delay wet sump and drainage before oil tank drained and TS cover replaced. Just turned engine over to see I was only feeling valve spring tension max and chain retained its set and oil does drain out crank end more in some positions than others.