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Old May 02, 2012, 10:21 AM
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McCoy .19 stunt engine

My mate has acquired a McCoy .19 engine. It is the CL version, with a red head.

Anyway, it ran very badly. I determined that it had been assembled with the incorrect orientation of the cylinder liner.

It now runs pretty well.

BUT. .. the piston has a machined protrusion on its crown; something to do with squishing, I expect. This protrusion is offset to one side, effectively screening the inlet ports from the exhaust ports. I'm sorry, I don't know the correct name for this protrusion.

My question is, "should the protrusion be closer to the exhaust ports, or the inlet ports. In other words, how do I tell whether the piston is correctly orientated?"

Hope that makes sense.

While you're at it, can you explain how this thing works?
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Old May 02, 2012, 10:51 AM
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Yes they call that style of engine a crossflow scavenged or loop scavenged engine.
The baffle on top of the piston is used to cause the air/fuel charge to loop up and over so that less of the air/fuel charge goes out of the exhaust port.
The baffle is located closest to the transfer port on the engine farthest from the exhaust port.
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Old May 02, 2012, 11:42 AM
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Ah, thanks.

I'd figured that was its purpose. Made the changes. It now runs like a good un.

Not a bad buy at 7... the previous owner thought he was selling us a knackered engine. It will be going in something vintagey.
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Old May 02, 2012, 01:38 PM
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That is a pretty good deal for you. They can be a lot of fun and they run pretty good too.
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Old May 02, 2012, 02:28 PM
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The McCoy Redhead 19 is a favorite engine. A friend had one on a Brodak trainer. It would fly the trainer, but not very well. It had the reversed liner as you describe. I've bought several cheap fleamarket engines which had the same fixable problem. I have several of the engines. I have one on a trainer which has had 100's of flights. It has no compression, but is usually a one flip start, given head prime and a choke, and runs to suit. Running all castor fuel, maybe 25% oil, will serve your engine well. Mine is running on Sig champion 10% nitro, 20% oil, half castor, half synthetic. Any expert will tell you that my fuel is not what is usually recommended.
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Old May 03, 2012, 02:35 AM
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These engines are not too common in the UK. Well, I've never seen one, in 20-odd years of model flying.

I dunno what fuel we were using... nothing exotic, though.

The only other McCoy I can recall, came with one of those plastic CL models ... late '60s, I think.
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Old May 05, 2012, 05:14 PM
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Feed it lots of castor, don't ever let it run lean. The McCoy P/L are relatively soft and will get wasted very quickly on a lean run.
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Old May 15, 2012, 09:20 AM
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I had one of these years ago and could never get it to run. Perhaps mine had the liner reversed as well.
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