I busted a spring a couple of years ago, and was still able to ride around for a while with no dramas until I got around to having a bo-peep...
I think it was making a bit of a clunk when I rolled it over with the kicker, but nothing much else untoward.....so having said that, I know the cams will still still engage without any spring at all, but can't remember if it still engages with a loose nut.
Even though I ordered a new spring of the correct number, I think I was sent the wrong one (for S/A), or it's just crap- shorter and a bigger diameter , so it doesn't sit on the sliding /fixed sleeves comfortably (in fact I used a short length of SS exhaust pipe to sleeve over the sliding bush and nut, these sleeves don't spin or slide- just 'space'), so I now have some lash and a clunk at times when engaging kicker, and or in and out of the 'dead-spot' between power-on/power-off- otherwise it rides around without drama- (except the previous mentioned minor slippage), but WILL change it when I find a better one(note to self).
I did a rant about it at the time- a search might find it, I'll try that later if need be.....but I don't think that's the problem of the clutch breaking loose; maybe owain you just over-charged the engine when you re-built it