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"Bumpy back" io-520?

Cardiff Kook

PATRON
Sisters, OR
Was inquiring to costs on an overhaul of an io-520 as part of my education for purchase of skywagon.

One shop said that the flat back 520's were not worth the cost to overhaul. Better to do a core exchange and get a factory new. Another overhauler said they could do it- but that shop is boutique and about 50% more for an overhaul than another reputable shop.

What exactly is the "bumpy back." and what is this "seventh stud" stuff. And
 
Was inquiring to costs on an overhaul of an io-520 as part of my education for purchase of skywagon.

One shop said that the flat back 520's were not worth the cost to overhaul. Better to do a core exchange and get a factory new. Another overhauler said they could do it- but that shop is boutique and about 50% more for an overhaul than another reputable shop.

What exactly is the "bumpy back." and what is this "seventh stud" stuff. And
Bumpy case is phase 3 stronger straight is phase 2 prone to cracking. Had one on a 185f I had in the 80s.same bumpy have 7th stud others can be drilled for 7th stud pad is there.
 
I had my IO-520 overhauled by a company which supposedly did work for Cessna. Short story, a nightmare which I nursed to the next overhaul time. Then, I upgraded to an IO-550. Fantastic improvement. In doing so I splurged with a new Platinum version IO-550 which I installed along with a new prop with the STC from Texas Skyways. Great people to do business with and less cost than others which also hold STCs for the IO-550. https://txskyways.com

You could do what I did or use a regular new engine or a remanufactured one. Texas Skyways sources their new engines through Air Power. https://www.airpowerinc.com
 
I had my IO-520 overhauled by a company which supposedly did work for Cessna. Short story, a nightmare which I nursed to the next overhaul time. Then, I upgraded to an IO-550. Fantastic improvement. In doing so I splurged with a new Platinum version IO-550 which I installed along with a new prop with the STC from Texas Skyways. Great people to do business with and less cost than others which also hold STCs for the IO-550. https://txskyways.com

You could do what I did or use a regular new engine or a remanufactured one. Texas Skyways sources their new engines through Air Power. https://www.airpowerinc.com

Interesting- talked to Victor Aviation- a very reputable overhaul shop and the owner thought the 520 was a better engine.

Maybe I will open another post on that topic
 
Bumpy case is phase 3 stronger straight is phase 2 prone to cracking. Had one on a 185f I had in the 80s.same bumpy have 7th stud others can be drilled for 7th stud pad is there.

My (around 1999) reman 470 came with one. When I converted it for a 520 crank for Pponk the oil transfer collar, 7th stud, and cylinder deck milling was required.
 
the small bolts on the top of the case that hold the halves together have bumps of extra material above them all the way down the case. so bumpy back. the others are a smooth front to back with no bumps on top
 
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