Is there an STC for a primer system for my engine?

Q: I have been looking for a possible STC to install a primer system on a O-320-A2D. Would you know of one?

JERRY BARNHILL, Longville, La.

A: Jerry, after checking a few things out, I discovered that almost all of the O-320 series engines were delivered from Lycoming with a factory installed primer system. However, the O-320-A2D is the only O-320-A series that didn’t have the factory installed primer system.

Please keep in mind that I’m speaking specifically of the O-320-A series Wide Deck Cylinder Flange configuration engines, where the engine serial number suffix is -27A.

If I had to guess why this specific model did not include a factory supplied primer system, it would be the airframe manufacturer didn’t want to pay the cost for the system.

I’d also guess that this particular engine was utilized in a high-wing airframe application and the airframe manufacturer thought the head pressure from the fuel tank would eliminate the need for a primer system. The carburetor also was equipped with an accelerator pump, so a pump of the throttle prior to cranking would aid with the starting process. Of course, caution must be used when doing this because excessive pumping could lead to an engine fire.

If you are really convinced you need a primer, I’d look into installing one using FAA Form 337 rather than an STC, which may cost you money to obtain.

I’d suggest you discuss this with your local FAA GADO/FSDO. I see no reason why this wouldn’t be an easy field approval, keeping in mind that I can’t guess how the FAA may respond. You can show the FAA that primer systems are common on most O-320-A and E series Wide Deck Cylinder Flange configuration engines as listed in the Lycoming Parts Catalog PC-203-1.


  1. Charles Culp says

    I never use the primer system on my O-320. I just pump the (throttle) twice – the accelerator pump inside the carb primes itself – then mine starts on 3rd turnover of the crankshaft.

  2. says

    I’ve researched this and found that in the case of Piper and Cessna singles both Lycoming AND the airframe manufacturer provide information on the installation of an approved primer system. And the two systems are different; in one case Lycoming specifies stainless steel tubing while Piper specifies copper tubing. The owner didn’t specify the airplane his O-320 is installed on, but I recommend he check the aircraft parts and service manuals for an answer.

  3. Greg W says

    I would agree with Paul. With the aid of your A&P/IA draw up an installation that will work based on a SIMILAR aircraft, be sure to indicate routing of the primer lines in relation to control and electrical wiring. Submit the drawing with a form 337 to your local FSDO and get a field approval. Field approvals are still obtainable, the different FSDOs and inspectors will want different amounts of documentation however as the process is not standardized. Remember the inspector at the FSDO,(air safety inspector), has to sign that your design will work, so make sure that they are comfortable with it. Most maintenance feds. are on our side, they want us to fly, but DON’T cut metal until you have approval.

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