Port & Polish etc for a “Performance” Engine

[A64Pilot]

Somewhere in a recent thread there was discussion on porting and polishing our aircraft engines. I have a Gann “performance” engine and was sure he did things beyond perfect balance etc but I didn’t know exactly what so I called and asked.

According to him most of the performance work is in the Cylinder of course, he does port and polish, but he’s not changing shape, geometry etc, what he does is clean up the largest port and them matches the rest to that one so you get identical cylinders, balancing the flow.

He also does a seven angle valve job. Rather than try to explain that it’s best you just Google it, three angle is common, I though we were hot stuff in the bike shop because we did five but Gann does seven. But multi angle valve jobs have similar effect to installing larger valves, that is you get more air into and out of the engine and make more power, it’s not trivial.

He also hones, not reams valve guides to a tolerance of .0001, yeah that’s 1/10,000, where I thought .001 was real good.

Then on the case they machine a groove where ALL the thru bolts go through and put a silicone O-ring there, that prevents oil seepage of course but according to him it’s real value is that it precisely locates the case halves.

If anyone is unfortunately needing an overhaul soon and wanting performance better than stock give him a call.

I did not ask what dyno differences there were etc., to me it’s my 360 is the smoothest running 4 cyl motor I’ve flown behind, beside my Mooney came with the engine.

I did not ask how much either.

https://www.gannaviation.com/home

[tgardnerh]

Then on the case they machine a groove where ALL the thru bolts go through and put a silicone O-ring there, that prevents oil seepage of course but according to him it’s real value is that it precisely locates the case halves.
https://www.gannaviation.com/home

This part seems risky from a regulatory standpoint--it's removing metal and adding something squishy in an area where preloaded is critical. (see the current thread going on oil leaks and engine cases)

Is it something that is within the scope of a&p discretion, or does he have specific approved data to do that?


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[N201MKTurbo]

13 minutes ago, tgardnerh said:

This part seems risky from a regulatory standpoint--it's removing metal and adding something squishy in an area where preloaded is critical. (see the current thread going on oil leaks and engine cases)

Is it something that is within the scope of a&p discretion, or does he have specific approved data to do that?


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I believe the O-ring modification is an approved Lycoming mod. I would have to look up the SB to be sure.

[A64Pilot]

46 minutes ago, N201MKTurbo said:

I believe the O-ring modification is an approved Lycoming mod. I would have to look up the SB to be sure.

I think it is partially, but not for all thru bolts, he’s doing all of them. But I could of course be wrong as I have not researched it.

Apparently some newer models of Lycomings come this way as in a few are O-ringed and through some process he’s obtained approval, Didn’t ask if it was an STC or what form of approval he has.

However his shop is a Repair Station which means they are under closer scrutiny than an average A&P is, so I’m certain he has approval ,but didn’t ask specifically. I wasn't buying an engine, know he’s busy and didn’t want to waste his time, nor make it sound as if I was questioning his Credentials.

 

Edited June 10, 2022 by A64Pilot

[tgardnerh]

9 minutes ago, A64Pilot said:

I think it is partially, but not for all thru bolts, he’s doing all of them. But I could of course be wrong as I have not researched it.

Apparently some newer models of Lycomings come this way as in a few are O-ringed and through some process he’s obtained approval, Didn’t ask if it was an STC or what form of approval he has.

However his shop is a Repair Station which means they are under closer scrutiny than an average A&P is, so I’m certain he has approval ,but didn’t ask specifically. I wasn't buying an engine, know he’s busy and didn’t want to waste his time, nor make it sound as if I was questioning his Credentials.

 

That's reassuring--somehow I had the incorrect image of a lone mechanic gone rogue, like that one who put sealant between the cylinder and the case leading to disaster. https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2013-04_a-little-dab-ll-do-ya-in.pdf 

[JimB]

3 hours ago, tgardnerh said:

This part seems risky from a regulatory standpoint--it's removing metal and adding something squishy in an area where preloaded is critical. (see the current thread going on oil leaks and engine cases)

Is it something that is within the scope of a&p discretion, or does he have specific approved data to do that?


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This is from a narrow deck O-360 we just removed from a Comanche. Is this what your talking about? All them had a o-ring and there is already a groove around the base of each thru bolt. 

[JimB]

Items 10 and 11

 

[N201MKTurbo]

Here is the Service Instruction that authorizes the O-rings. There is another Service Instruction for adding O-rings to doweled crankcases.

http://nebula.wsimg.com/e25dfd622fa874f440fa6d8f405274d6?AccessKeyId=4F9A3E91CE7CAB506B89&disposition=0&alloworigin=1

 

[GeeBee]

I had a Gann engine in my PA-18. A 160 hp O-320. Ported, polished, balanced.  It dyno'd at 173hp. Best running Lycoming I ever flew. Way beyond smooth. Carlus Gann used to be a NASCAR engine guy for Bill Elliot. He is one of the few mechanics I know that has a "P". Not an A&P, but just a "P" rating because he is all about engines and he knows them like nobody else.