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OS GT33 Issue

Old 05-04-2016, 02:47 PM
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Default OS GT33 Issue

I have had incredible performance from this engine over the past five years. It turns really large props at very useful rpm for what I do (around 7k on an APC type 21x10 PN, on avgas), and displays outstanding midrange torque, where I do most of my flying.

However, an issue has occurred twice on the same engine. Last November I recall a slight backfire on run up while on the flying stand and the engine flamed out almost immediately. The prop would not turn free and upon disassembly I found one circlip that holds the wrist pin in place, gone. The engine ingested it destroying piston, liner and ring. I replaced these parts and flew the engine exactly 10 flights over the past couple weeks.

this past weekend, the engine seized again. Before it seized I heard a metallic noise like something got caught in a fan and then the seizure. It was idling so I hoped for minimal damage but not so....piston and liner are toast again. Failure mode was the same....the wrist pin retaining clip popped off and was ingested.

I know two other fellows whose 33s have had the same exact problem. Has anyone else had this problem with their 33?

This appears to be an OS issue. I'm trying to work something out with Hobby Services. The warranty period has lapsed on this engine but to me, it's a design issue. Wrist pin retention clip technology is old and proven so it has to be groove depth and circlip design. It might also be that the clips are breaking from hydrogen embrittlement.

I love this engines performance and it's easy field manners. And until last November, it was absolutely dead reliable driving my e power friends nuts....gas up, two flips, fly, repeat. Needless to say, this issue is a serious concern.
Old 05-04-2016, 06:35 PM
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Ouch! Best of luck on the outcome of your issue here Matt.
Old 05-05-2016, 06:50 AM
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Please keep us posted on the end cause and remedy ,so we'll know what to look for .
Old 05-18-2016, 02:14 PM
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I sent the damaged engine to Hobby Services. They sent me a new engine.

Thank you Hobby Services
Old 06-05-2016, 06:59 PM
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Just wondering, maybe Teflon buttons could be used to prevent cyl damage? Just a Idea?


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