What is the precise reason for the 5 minute limit at 5800?

I am not a Rotax design engineer so do not know the reason for the limit...However

Not all temperatures in the engine are measured. After over 100 years we still do not have a reliable way of directly measuring Piston temps. Often ICE engines are limited by this, melting a piston is not a good thing. Keeping Pistons cool is difficult, spraying oil onto the bottom of them is one method, cooling the inlet charge with water/ethanol injection is another. Ceramic or Carbon pistons have been tried but are very expensive and difficult to make.

Secondy as "heat soak" increases so does problems like pre-vapourisation and Detonation.

In the end Engineers usually set a reasonably conservative operational advice so you "may" get away with longer without problems...or may not. In an Aircraft it is usually best to follow the advice.

If you want higher take off performance lighten the load and go on a diet ! I have recently lost 20lbs and the difference is noticable !

Thanks!

An engine can only take so many rpm's and stress caused by them. So the engine Mfg's early on probably tested their engine to destruction and they run them for hundreds and thousands of hours. Then you wouldn't want to sell an aircraft engine that goes right to a destructive state for the public. So the Mfg has to find an rpm that and engine can safely run at and then since our engine reliability can mean life or death then a safety factor is also added in to reduce the rom, but still make the engine develope a good strong workable engine, rpm and HP. Could your engine take more, yes, but you'd be foolish to risk engine destruction just for a few more rpm that won't give you that much more gain. Plus you then risk an $189K engine and possible injury or death for you or people on the ground. 

Trying to get more rpm would be a foolish endeavor not to mention you'd have to deal with prop issues.. 

Roger Lee wrote:

An engine can only take so many rpm's and stress caused by them. So the engine Mfg's early on probably tested their engine to destruction and they run them for hundreds and thousands of hours. Then you wouldn't want to sell an aircraft engine that goes right to a destructive state for the public. So the Mfg has to find an rpm that and engine can safely run at and then since our engine reliability can mean life or death then a safety factor is also added in to reduce the rom, but still make the engine develope a good strong workable engine, rpm and HP. Could your engine take more, yes, but you'd be foolish to risk engine destruction just for a few more rpm that won't give you that much more gain. Plus you then risk an $189K engine and possible injury or death for you or people on the ground. 

Trying to get more rpm would be a foolish endeavor not to mention you'd have to deal with prop issues.. 

I am talking about the 5500 max continuous limit not the redline at 5800.

I was just curious but not trying to force my engine to do more than it is meant to.

The 5500 max continuios is fine. Rotax has tested this and so have many users for decades. They have a safety cushion in their numbers. Like many Mfg's that's to keep reliability and longevity and keep people from losing their engine. All engine Mfg's have safety and liability limts designed for their engine.