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Port and polish

AK56

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Just wondering what a port and polish job should look like. These were done by a shop in Palmer. They ported the heads and exhaust guide and valve seat. I don’t see any polish. Am I missing something?
 

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These are what mine looked like from LyCon.
 

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That looks more like I expected them to look like. Mine looks like somebody hogged the material out and sent them out.
 
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Far as I know, any overhaul of a certificated engine must be done in accordance with the factory overhaul manual.
What I've always wondered is how these shops can do a "port and polish" job, which I'm pretty sure is not in the manual.
Is an STC required?
 
Far as I know, any overhaul of a certificated engine must be done in accordance with the factory overhaul manual.
What I've always wondered is how these shops can do a "port and polish" job, which I'm pretty sure is not in the manual.
Is an STC required?
Why would it be a major per the far’s if they don’t claim it’s increased power but a power balance for the pulses? Removing casting flash and minor cleanup that doesn’t affect strength or structural integrity could and is considered a minor change.
 
Why would it be a major per the far’s if they don’t claim it’s increased power but a power balance for the pulses? Removing casting flash and minor cleanup that doesn’t affect strength or structural integrity could and is considered a minor change.
Typical FAA deal. One shop I know has the FAA's blessing and another shop can't do it on certified because of the FAA. 🤷‍♂️
 
If it runs lean after just a P&P job - same setup otherwise - expect more air flow/volumetric efficiency? Doubt anybody knows much before then after.

Edit: Here's one opinion> https://www.aviationconsumer.com/misc/trick-cylinders-porting-and-polishing/ W/O a flow bench and CC'ing the combustion chamber volume, matching cylinders might prove a challenge. Run a restrictive intake (and air filter) plus exhaust, or allowing gaskets to interfere with flow, and it may not work as well as it should.

If you want further info get a copy of J. Schwaner's excellent Sky Ranch Engine Manual (one source of many). Page 108 on discuses this topic. It's a must read for pilots.

Gary
 
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Making each cylinder uniform - intake and exhaust flow plus balanced components - should make it smoother. Power can come from the P&P to some degree (see the links in #16), but usually from new cylinder components. I'd be looking at a few directly measurable things before and after. Like any 4-point EGT/CHT alteration (more uniform and ?), static run up numbers (higher?), and improvement in rate of climb (higher?). A quality prop balance should directly inform about smoothness, ideally also before and after.

Gary
 
Shape is everything. Too smooth and sticky boundary layers line the port walls. A bit of texture is good, think golf ball.
 
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The Sky Ranch Engine Manual recommends a textured intake (see the golf ball analogy above), but a smooth exhaust to support high velocity flow and reduce carbon formation. Once roughened via deposits, exhaust flow can be slowed it's claimed. Get the manual it's worth reading.

Gary
 
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