Can we convert from dual mag drive to separate drives?

Can we convert a Lycoming O-540-J3A5D from dual mag drive to separate drives? Can it be done on a 1980 Dakota 236?

Our club, The Flying 20 Club of Danbury, Conn., has three planes, a Dakota and two Archers. Recently,during the overhaul of one of our Archers, N8198P, we had the plane equipped with the new LASAR variable timing ignition system. Our experience with this new unit during the first few months has been more than pleasing. The plane has much improved performance. Initial climb is up from around 800-900 feet per minute to a really remarkable 1,200 fpm. Cruise at 75% is strikingly better. In fact, we found that on a cold and bumpy day, setting 75% power — as we are required to do during break-in — pushed us uncomfortably close to the yellow arc on the airspeed indicator. This is phenomenal performance, especially considering that the LASAR unit only added about $3,000 to the cost of the overhaul.

We expect to overhaul the Dakota in late 2007, based on our current hourly utilization, and we would like very much to equip this engine with the LASAR system as well. Here’s where the rub comes in. LASAR does not make a unit for a dual drive mag engine. If we could convert the engine to run separate mags we believe we’d be home free on this issue. We realize that the conversion, if it can be done, would involve swapping the accessory case and, perhaps, other modifications as well. We’ve searched for STCs for this mod and so far no luck. Can you enlighten us on these questions?


Club Maintenance Officer

I think I’ve addressed this subject in the past, but feel this particular engine model may present more of a challenge.

First of all, to answer your question, yes I believe it can be done, but with caution prior to spending any money. Lycoming has been offering exchange engines for customers who want to convert from the single dual drive magneto configuration to one that utilizes two individual magnetos for several years now.

However before you jump to order yours, let’s look at some of the things that should be taken into consideration first. To my knowledge Piper never certified a model O-540-J3A5 using two individual magnetos in a production aircraft. The first thing I’d recommend you do is have your maintenance facility check with your local FAA FSDO office or its Principal Maintenance Inspector (PMI). He should be able to confirm that since you were unable to locate an STC for this conversion that it could be done under a one-time field approval on an FAA Form 337. This would permit you to remove the present model O-540-J3A5D and install an O-540-J3A5.

With regard to the Unison Slick Mag LASAR system being installed, this too should be doable, but you’ll have to check the Slick STC to make certain the O-540-J3A5 engine is included. That will be the key to proceeding with this conversion.

If the O-540-J3A5 is covered under the Slick STC for this model, then it’s possible to order your exchange engine from Lycoming with the LASAR system installed by the factory, making your installation easier right out of the box. If it isn’t on the STC, you can still install the LASAR system by going the FAA 337 route. The FAA PMI can provide you with the requirements.

Caution: Be certain to ask lots of questions before you spend any money!

I think this can be accomplished, but you may have to jump through some hoops first.

I’d like to revisit my Feb. 16 column, “”Can I install a constant-speed prop on my engine?,”” in which I answered Wade Sullivan’s question regarding the installation of a constant-speed prop on a Lycoming O-360-A3A in his Cherokee. A former colleague at Lycoming and another faithful reader set me straight and advised there was an O-360-A3A installed in the Piper Cherokee “”C”” Model.

Therefore Wade, I’d say it should be no problem to convert your engine to incorporate a constant speed prop in accordance with the Lycoming Service Instruction 1435, which will serve as your approved data.

Thanks to those who set me straight and good luck, Wade, with your conversion.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:


  1. Sammy Lee says

    Hello Mr. Paul McBride, We have a Piper Lance N772SG with IO-540-KIG5D engine as you know has a single dual magneto and we want two separate magneto’s. Is there and STC that would fit our Piper Lance and Lycoming engine to do this all with regulations? Thank you for your time. Respectfully, Sammy Lee

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