Berling Magneto Overhaul

Berling D81 X2

The Berling Magneto overhaul is done!  Before I get into the details, a little about the magneto.

The OX-5 used both the Berling and Dixie magnetos.  My engine came with the Berling, so that is what I went with.

The specific model is a D81 X2.  It's typical of early magnetos - horseshoe stationary magnets and a rotating coil/armature.  The rotating coil magnetos produced a good, hot spark, but were eventually replaced with the ones we know today that have rotating magnets and stationary coils.  It's my understanding that the rotating coils failed sooner due to the inertia and heat they were subjected to.

A magneto with 2 poles (horseshoe magnet like on the Berling) needs to operate at 2X engine speed on an 8-cylinder OX-5.  You can actually calculate the speed a magneto needs to operate at on an engine by using the formula:

Speed = (no. of cylinders / 2) divided by (no. of magnet poles)

We have to divide the number of cylinders by 2, since a 4-cycle engine makes 2 complete rotations per spark plug fire.  The distributor rotates at 1/2 magneto speed since we have to fire all 8 cylinders during the 720 degrees of rotation.

The Overhaul

Magneto in unrestored condition

The magneto I started with was original to my engine and was in unrestored, never overhauled condition.  So I was confident I had all the parts, I just wasn't sure what condition they were in.

Housing stripped and cleaned - ready for paint

The first steps in any overhaul/restoration is to clean and inspect the parts.  It's amazing when you look at these 100 year-old parts the effort that was made to make them.  There is no way in todays time that castings would be made that are this intricate - a beautifully made part!

Tool to remove the end cap of the adjustable bearing assembly

If you are going to take apart one of these magnetos, you'll need a couple of special tools that are used on the adjustable bearing assembly that supports the distributor gear.  They are easy to make.

The first one, shown to the right, removes and installs the cap that secures the 2 internal roller bearings.

Tool to remove the shaft nut

The next tool required is to remove/install the nut that holds the internal shaft in place.  The distributor gear attaches to this shaft, and the distributor finger goes thru the inside as well.  This is just a 1" socket that has the O.D. ground down to fit inside the housing of the bearing assembly.

Rewound coil/armature assembly

A couple of other components required special attention.  You may recall from previous posts that I had the coil rewound.  The original one checked out fine electrically, but I just don't feel comfortable flying in an aircraft with one magneto, that has a coil 100 years old!  Here you can see the rewound coil and the original laminated condenser replaced with a modern, solid-state type.  The spool to the left of the coil, is the collector spool that sends high voltage from the secondary coil to the distributor assembly.

Interrupter assembly

The interrupter (points assembly) was completely gone thru.  I disassembled and cleaned all the components and even had a new set of contacts to install.  You'll want to make sure the contacts are adjusted to make even and complete contact with each other. 

Cracked distributor finger locator bushing

One of the weak points of the 
Berling...the distributor finger and the locator bushing for the finger (shown to the left).  The finger is a long spindly shaft that needs to be inspected carefully for any signs of cracks.  The same for the locator bushing.  

It's hard to tell in this picture, but there is a crack that runs thru the mounting bushing and partially up the side.  If this were to come apart during operation - the magneto would fail.  Having spare parts, I replaced it with a good one.

 

The distributor finger (right), and locator bushing (lower left) are shown in this photo.  Inspect these carefully!

All the components, cleaned, inspected and ready for assembly

Finally, after all the cleaning, inspecting, replacing, etc. all the parts were ready for assembly.  The magneto goes together quickly and easily, but does require some care in a couple of areas which should increase the reliability of it.







Assembly

Shim being installed under bearing race

One of the first things to do is adjust the end-play of the armature.  There are no specs for this, but most magnetos I'm familiar with are adjusted with no perceptible end-play, but yet do not bind when rotated.  The end-play is adjusted with shims below the inner bearing races that are pressed on the armature shaft.  This requires a lot of fiddling around, as the shaft has to be installed, removed and re-shimmed multiple times to get it right.  Mine required a .004" shim to remove any end-play.

Internal timing marks

The magneto is timed internally, by aligning the marks on the armature shaft gear and distributor gear.

Clay being used to check clearance between distributor finger
and distributor

Distributor finger components showing nickel contact and shims

The Berling magneto utilizes jump spark distribution in the distributor block.  This means there is no direct connection between the distributor finger and distributor, the sparks jump - no different than in a spark plug.  Close clearance is important here so as much energy as possible goes to the spark plugs.  I checked this gap with clay, and adjusted the nickel contact in the distributor finger with shims.  I found the segments in the distributor block were not consistent, so I ended up with around .010" clearance, but no less.  I wanted to make sure there was never any contact between the two.

Puller required for removing bearing race

Oil groove machined into end plate to feed oil to bearing

The bearings in this magneto are manually oiled.  It's important the machined groove in the end caps are not plugged and feed this oil to the bearings.  The only way to know this is to remove the bearing races from the end caps.  You need a special puller to properly do this without damaging anything.  This picture shows a typical puller.  

When I got the bearing races out of mine, the grooves were packed with dried, thick oil residue.  These bearings would not have been properly lubricated.

Magnets being charged on magnet charger

With all these details out of the way, the magneto could be assembled and the magnets charged.  You can refer to a previous post on the magneto charger, but if you recall, I mentioned it was built to charge the magnets on the magneto.  That way you don't have to use a keeper on the magnets as they are installed.

My friend Mark bought a gauss meter (measures the strength of magnetic field) that he could use on his Model T magnets.  I decided to use it on this setup to see what effect the charging had.  Depending where on the magnets it was measured, the strength doubled from about 100 gauss to around 200 gauss after charging.  I don't really know if that is good or bad, but doubling seems good and the coming in speed would tell if that is adequate.


Completed Magneto

Completed magneto - ready to make the OX-5 Purrrrrrrrrrr!

Berling D81 X2 nameplate

Here are some shots of the final product.  She's a heavy one...weighing in at a whopping  19.5 pounds!  All that's left is to put in on the test stand and see if it will make some sparks.

On test stand with spark plugs

On test stand with electrode-type contact points

I tested the magneto with both the spark plugs I am going to use on this engine and the normal contact points that are on the test stand.  The magneto ran great, with a coming in speed of about 120 RPM.  I need to tweak the stand for more prolonged running as I would like to get several hours of run time on it prior to being used on the actual engine.


Final thoughts

If you read just about anywhere, the Berling magneto does not get much love.  Many people have opted for a more modern Scintilla or Bendix magneto, but those, being a 4-pole magnet, have to run at engine speed so a gear box is required to gear the magneto down.

I can say after overhauling this one, my level of confidence is greater than it was before.  Being able to carefully select and fit all the components will likely improve its reliability.  It is simple in construction, but yet has a lot of parts.  One thing I do like about it, is that it can easily be opened for inspection even on the engine.  So, we'll just have to see - time will tell!














Doing a little bit more cylinder work - honing the barrels and a little mod. to the water outlet that I will talk about on the next post.  Don't touch that dial!