[GMAs]

Well ... how to say this...

If the engines look good ... isn't leaking oil or buring it real bad.. and the seals look good.. and you are using it under part 91... you don't have to take it down because of age... so long as it meets the power requirement... but,,, with that said their is always another side to the coin...

after so long the protection (alodine) on the outside of the engine goes away... and the bare metal will start to pit and errode away... making the cases weak and subjuct to failure...

the rubber seals under the cyc's bases are not able to be seen... and because they are exposed to a higher than normal heat... they get harder and harder.. and lose their ability to spring back.. so the cyc get lose and start wearing the case flanges... steel parts inside which used to be plated are now starting to rust... like the push rod tubes... and then their is the ever present varnish that comes from the inactivity and the fuel... that want to stick the valves to the guides... causing excessive wear on the lifters and cams'... rust in the cyc and .......

the most important item we have seen is when the engine sits... the getter goes away... yep the major reason we thing lead is still in avgas... as the lead coats the exhaust parts... forming a protective coating which the sulfer products and acids can't get to.... having a engine not run... will cause that getter to go away... and thus leave the alu and mag metals to start to erode away... here we can see it in the exhaust attachment point on the cyc... and you suddenly get a exhaust leak.. droping the pipe you find that their just isn't any metal left to have the gasket seal up against... it all gto etched away from the errosive gasses and actions...

Now lets take a look at the outside of the engine... the gaskets.. get hard.. the fuel pump gets worn... and the nuts and bolts start to rust as the cad plateing goes away..

RUST is the pitting and oxidation of the metal... if you take away or etch in... you don't have the strength of the metal part any more... and sudden breakage is not good.. for cyc's.... hardened shafts inside start to rust and pit.. losing their strength... and gears and their teeth.. start to lose their hardness...

So what does this lead to... well if the engine is still producing power... then the rules say you can keep going if you want... but, then again we say how reliable is the engine... and that equates to safety... and failure in flight... i.e if you suddenly get a exhaust leak... could you go down in flames or will the gasses make you go to sleep and fly into the mountain or ocean...

All of these things have been weight in by the manufacture and he says that after so long... it should be over hauled and that he set the standard by which one does it....

Can you use them..yes... do you want to use them... see above and read again.. then come back and let us know... GMAs