15 year life span

Hi George

TBO is actually one of 2 things....we always tend to think it is only hours but in reality it is hours OR time.  Hours are easy to understand, that represents wear in the engine and in general we overhaul before things begin to wear our.  Calendar time is for age of the parts within your engine that time out by years or months.  Rubber parts for example can degrade with time.  In addition engines with very infrequent use like low hours can start to corrode internally with time.  This is why TBO is one or the other, whatever you reach first. 

Cheers

If all is well now, just continue to run it "on condition". Continue with proper maintenance (5 year rubber replacement, etc.) and pay even more attention to anything that seems to be deteriorating. TBO is just a factory recommendation, not an FAA requirement for non-commercial flying. There are several highly respected A&P/IA's that recommend this approach; Mike Busch for one, who does many of the EAA engine webinars.

In my jurisdiction under my licencing regime I can legally continue to run on condition. You can take a view as to whether that is wise technically based on the engine's history, the operating environment and its condition. Under other licencing regimes you cannot run beyond TBO.

My 912ULS has 1008 hours and has been flying for 15-1/2 years. I've replaced several leaking coolant o-rings and of course the 5 year rubber thing thrice. On condition and be safe are a couple of my mottos. Oh yeah...and keep 'em flying. I fly an hour or so almost every weekend. 

Alan

Hi all

I am glad to see some discussion on the topic especially since there are opinions and flying an experimental you can always do what you want.  For aircraft under special light sport you are governed by whatever the OEM put in his manuals.  The FAA leaves it up to them to determine such things.  For the most part we have seen the OEM defer to the Rotax manuals for maintenance and the like when it comes to the engine.    Liquid cooling, construction materials, and many other considerations suggest that advice would be better to get from the actual people who work on them all the time.  Just my 2 cents on that part, take it for what you want. 

On condition implies that you have some type of inspection process or plan.  Outside the USA you need to provide a written plan of what on condition is, how you will verify that your engine can exceed the recommended time or hours of engine life.  I like following the Transport Canada airworthiness notice b041 as a good example of a program if you go that way

https://tc.canada.ca/en/aviation/reference-centre/airworthiness-notices/airworthiness-notice-b041-edition-4-31-march-2005

At the very least this should be started before you reach your hard time, not at TBO.  You need to establish a baseline and that should be when the engine is not over limits already.  On a Rotax, particularly due to the gearbox and dry sump oil system, you need to consider a corrosion inspection of the gearbox and internal parts.  At the very least on your annual after you are over your hard time it is best to remove the gearbox assembly and do a visual inspection for corrosion.  (you only will need to inspect the assembly and not disassemble the parts inside)  In addition pull one cylinder and do a borescope check of the crank, camshaft and internal parts to verify there is no internal corrosion.  Engines that have low running hours but high calendar time are far more likely to have corrosion issues than those that are run on a regular basis. 

One last note.  Coolant hoses fail from the inside out generally.  This is why they have a calendar time life and not hours.  it is difficult to inspect hoses that appear good on the outside and say they will not fail.  The number 1 failure of coolant hoses is ECD, electrochemical degradation, due to electrical discharge from the flowing hoses and types of metals used in the engine.  This can cause electrical discharge that creates fissures inside the hoses and weaken them leading to failure at some point.  Consider also the coolant types as the older iAT coolants actually are electrically active and can cause excess wear inside the hoses.  (consider using OAT or HOAT coolants for this reason) 

Anyway, big topic, good to consider your options.

Cheers

ELECTROCHEMICAL DEGRADATION (ECD)