engines
 

I should know this really but here goes, can anyone tell me, on a light aircraft, thats being used for ariel work, is there a maximum amount of hours before the engine is replaced?, and if so, is it re-conditioned, or brand new? cheers, max.

In the uk under the light aircraft maintenance schedule engines can be run 20% over the makers TBO provided that it,s condition is OK.
It is not usualy a good idea as the overhaul cost is normaly higher than if the engine is overhaul is done at the recomended time.
Overhaul means that the engine is rebuilt to ovehaul limits and NOT to service limits and to the latest SB state.

Just for your info the Lycoming 0-235 a la C152 has an overhaul life of 2200 hours, although some Lycomings have a life of 2000.
Dependant on compression etc, a top end overhaul may prove necessary before the zero timing by overhauling is required which costs about £7k++ whereas a factory fresh lump is £20k ish. Feed throttle gently!!