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Old Nov 17, 2012, 01:16 AM
surfer_kris is offline
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It is the piston to cylinder fit that wears and it will not seal. It may well be a combination of the castor being a thicker oil and also being able to build up a varnish that both helps to improve the piston to liner seal on iron/steel constructions.

On engines with excessive crank to case slop, like the AP wasp, the thickness of the oil can also help to seal at the crank, without forming a varnish layer.

I'm not dissing synthetic fuels overall or without trying it, they have their place. I do run all synthetic fuels in ballbearing, ABC engines, and have had no problems with that. But I would never use it for iron/steel constructions, where to me the castor is necessary and was the fuel used when the engines were ones developed.

For obvious reasons I don't test and prove this every weekend. But let me give you an example that certainly has had me convinced. I was visiting a friend and we vent flying at his local field. There was another guy there with an Enya engine that he struggled with. It had no compression at all when turned over by hand, although it would occasionally fire when turned of with an electric starter, it would not stay running. I asked him about the history of the engine, and it had been donated to him from his friend who could never get it too run. He said the engine had been run-in, very carefully, on his regular all synthetic fuel, and the compression was only getting worse and worse. I then convinced him to try regular FAI fuel (80% methanol, 20% castor, 0% nitro). The engine would then run well enough that he could fly and it would also have compression when turned over by hand. The guy thought this was some kind of magic trick, and could not wait to tell his friend about it...
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