Old Doyn STC SA3-13 for O-340 in 170/172

3 weeks 1 day ago #3542 by STEVE ELLS
Replied by STEVE ELLS on topic Old Doyn STC SA3-13 for O-340 in 170/172
Hi Shannon;
I've only seen one other 170 with the O-340. In fact I've only seen one O-340.
Ask your mechanic to check to see that the prop governor hits the high pitch stop with the cockpit control pushed to full rpm. If it does, I suspect you have a magneto, or a magneto installation problem.
If the mag isn't timed right to the engine when it's installed, the engine won't make full power.

Let me know what you find.


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  • Shannon Moon
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4 weeks 1 day ago #3540 by Shannon Moon
Old Doyn STC SA3-13 for O-340 in 170/172 was created by Shannon Moon
I've got a 56 Cessna with this STC for a Lycoming O-340 and CS prop. I've run into an issue and am hoping there is someone out there with this STC that can help me with some info.

I recently had new mags installed. Afterwards my prop wasn't cycling properly. A local mechanic removed the prop governor and sent it to a specialty shop. One thing that was odd was the arm connecting the prop control in the cockpit to the governor.it had a bend in the middle, evidently to accomodate the angle at which the governor was mounted.

The prop sent back the governor with a standard arm, but the mechanic couldn't get it hooked up properly, and reinstalled the original unusual arm. Unfortunately I can no longer get full rpm at full power, I am out 150-250 short of the 2600-2700 RPM I got at full power (MP is still fine).

I only have minimal documentation for the STC, just the cover sheet, the tag for the kit in the logbook, and an ancient scanned blueprint for both the 170 and 172 titled "Doyn aircraft installation kit drawing #1099). There is really no info about the governor installation or the arm on the drawing.

I am hoping someone out there with this STC could help me out with some photos of there installation and info on there governor and arm, or maybe more detailed documents on the installation itself.

My plane is currently grounded, and I have 5 weeks til the schedueld CFII checkride I was planning to take in it. Any info would be greatly appreciated. The current holder of the STC (D'Shannon Aviation) says they have absolutely no info available on the STC.

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