Curtiss Jenny Restoration

Welcome! We hope you enjoy following the restoration process of a 1918 Curtiss JN4D Jenny. Once completed, the aeroplane will be flown and displayed at the Candler Field Museum in Williamson GA (30 miles south of Atlanta). You can contact me below by clicking on "VIEW MY PROFILE"

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Location: Peachtree City, Georgia, United States

Monday, November 18, 2013

Timing Hisso Magnetos

I wanted to post this for future Jenny restorers. We have learned a lot about timing Hisso magnetos and wanted to share our findings.  We ended up changing from the Champion tractor spark plugs to the more commonly used C-26 type plugs found on many Continental A-65 engines.  We tested the combination by taking a spark plug hooked up to its respective wire and touching it to the case of the mag.  With a good spin of the gear by hand, we saw good spark!


 The first step of the timing process is to get the left front cylinder piston all the way up to the top. 


You can use a Time-Rite tool, or a wire or just take a flashlight and look in the top spark plug hole to see the piston. I was amazed how good you can see inside there.


Turn the propeller until the piston is at the top and both valves are closed (compression stroke).  Mark this as zero degrees on the protractor.


According to the Hisso manual, the cylinder fires at 25 degrees before the piston reaches the top, called Top Dead Center (TDC).  Our engine is unique.  Most Hissos fire at 20 degrees but the E2 model fires earlier. Anyway, rotate the propeller back and then to eliminate gear lash, rotate it forward until 25 degreed before TDC.

 

 The magneto itself has to be internally timed.  The Hisso manual doesn't mention anything about this! I was able to find guidance in the Dixie 800 Magneto manual.

 


The manual specifically states that the mag should be set to fire at position "H" for our engine. That is about the 1 o'clock position on the magneto cap when viewed from the rear.

 

 Off came the cap.

 

 Here is the inside of the cap.  


 The timing light was hooked to the p-lead and the case.

 

Rotate the gear until the rotor approaches the "H"  position.

 

When the points will just start to open - this is exactly where you want it!


When the points open, the light goes on.


Yup, the rotor is right at the "H" position.


Now don't move the magneto!  It is set up to fire the "H" wire which correspondingly fires the front left cylinder which we conveniently set to 25 degrees before TDC.

The mag sits on a rail and cannot move.  You must gingerly put the mag in place without letting it turn. 

Below, you see a coupling with a spring and a cotter key between the mag and the engine.  Once the mag is in place, the gears must line up.  If they don't, there is an internal spring in the coupling which allows you to pull up the coupling, rotate it a little and push it down when the gears mesh.  The cotter key locks it in place.

 

 Above is a picture of the timed magneto in place. 

When we began timing the second magneto, a small piece of metal fell out of the back!  The clip that held the points in place had broken.  Luckily, I had another one from a spare Dixie magneto.


So, time the other magneto the same way.  When they are both installed, you can check it with the timing light.  There you go!  That is how you time a Dixie 800 magneto to the Hisso engine.

I know this is pretty dry stuff...and you are waiting for news of the first flight...but be patient.  I want to run the engine a few more times to set the idle, taxi around a bit, and when the conditions are favorable, take her up.  Stay tuned!

Brian

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