Normally the bolts stretch slightly when you torque them up - this keeps the tension in the bolt and holds down the head firmly.
If you reuse the bolts (as the mechanic who did my mums car found out) then they are already stretched and while they seem to tighten to the desired torque, the extra "stretch" from the previous tightening has made them slightly longer thus not clamping the head on to the required tightness.
If you torque them correctly surely the bolt being a slightly different length is irrelavant? You're still tightening it to the correct torque. The real danger is one of the bolts could snap when you're tightening them. I used the old head bolts when doing the head gasket on a 1300cc Golf and its still going fine. Probably more important with a bigger engine.
Sounds exactly like my Golf did when the gaskett went. You could also remove the plugs to check for signs of water. You're going to have to take the head off again so it might be worth getting a pressure test done to check for cracks? Not sure how much this costs, wouldnt expect it to be much.
well at the moment it is swings and roundabouts the pressure test is £80 the plugs have been taken out and there is no signs of water oil on one of them? but a new engine is £150 so sort of firing toward the new engine at the moment the engine is lucky if it has run 10mins with the new gasket and old bolts
I didnt realise a pressure test was so expensive. Strange that there's no sign of water on the plugs, for steam to come out of the exhaust there would have to have been water in the compression chamber and you'd expect to see signs of it.
For the difference in price between another engine I'd go for the new engine - what sort is it by the way? You could even use the head from the new one, get a new gaskett (and get some new head bolts ) and fit it to the existing one.