Why did exhaust bolt fall out after hibernation?

[Duke Caboom]

My old motorbike has spent 15 years in the garage, unused. Previous to that I used it sparingly but regularly for several years.

After a bit of fiddling I got it running yesterday. After about a minute of running one of the exhaust bolts fell out. This has never happened before.

Obviously its an easy fix, but I wondered why? Did the head to exhaust gasket shrink, leading to the bolt being loose and being vibrated off? Something to do with expansion as things warmed up?

If relevant its a 500cc air-cooled single, 4 stroke. Garage is dry and, while not heated, tends to be warmer than outside in winter.

Thanks

[E-bmw]

My best guess would be random event that could have happened at any time and was probably loose for some time.

Don't over-think it.

[paul_c123]

I imagine a 500cc single will act like an impact driver on EVERY bolt of the motorbike, so everything needs to be torqued properly to spec or it will eventually vibrate and fall off. It was only a matter of time for that bolt.