Radne Electric Starter Disassembly

This shows the disassembly of the electric starter that is supplied with the Radne Aero 120.
Radne Electric Starter
This starter is manufactured in Italy by Fiem. It is listed in their PDF Catalog.
(If that link is not working, there is a cached copy here.
The Swedish Aerosports NRG (and probably any e-start Radne) uses the 3MG16552 Model Number starter.
There are a total of four screws and one nut that must be removed to disassemble the unit.  This shows the 4 screws:

4 screws to be removed

The nut that must be removed is part of the postive electrical terminal.  Pop up the protective cap that covers the terminal nut, which will allow access to remove the nut and then the terminal/insulator components.  Note the skirt (indicated by the red arrow in the 4th pane).  This fits between the terminal stud (red arrow in 3rd pane) and the housing, and has the important purpose of insulating the positive terminal from the negative (ground) terminal.  Be sure this is properly reinstalled on reassembly, to prevent a short circuit.
NOTE: I received the following helpful comment/update from Peter Mack of Airtime Products:
On the flange of the pressed stator housing you'll find a centre punch mark near one of the holes. The motor must be re-assembled with this punch mark in the same location as it was originally or the poles will not be in the correct relation to the brushes and the motor does not spin. At least that's what I find.
You might also mention that the cap for the positive terminal insulator is glued in place these days and takes a concerted effort to get out.
Removing Terminal

With the 4 screws and terminal nut removed, the nose casting may be removed.  The Bendix gear assembly may then be lifted from the starter motor.  If you later find two washers (that may fall off during the dissaembly), they fit on both ends of the Bendix gear.
Removing the Bendix assembly

The figure below shows the complete Bendix assembly. The Bendix serves to automatically engage and disengage the starter from the flywheel teeth.  Grasping the Bendix gear teeth (when assembled to the starter) and rotating the gear will have two results, depending on which direction you rotate the gear.  In one direction a slip clutch will simply allow the gear to rotate about the shaft - this is what happens when the engine starts and the flywheel teeth are moving faster than the starter motor can turn them.  In the other direction the Bendix gear will move outwards along the shaft, and once it has reached the end of it's travel, further turning will turn the shaft and starter motor.

In operation, the motor rapidly reaches full operating speed.  The Bendix assembly has a fair amount of inertia, and it is therefore easier for it to move outwards along the shaft than it is to suddenly rotate at the starter speed.  This initial 'snap' is what causes the starter teeth to engage the engine flywheel teeth.  Once engaged, and a load is applied between the gears, the load serves to keep the Bendix extended.  When the engine starts, the load between the gear teeth reverses, as the flywheel teeth are now moving faster.  This causes the clutch to slip and also to push the Bendix assembly back towards it's resting position.

 Further disassembly will require compressing the spring and removing the locking ring from the groove on the shaft.  Removing and replacing this ring was the most difficult part of the whole procedure.
Bendix disassembly

The figure below shows what appear to be centrifugal weights.  A circular spring keeps them compressed against the shaft, and presumably, at some speed, these weights will move outward.  The left pane shows the assembled unit, the right pane shows the spring removed and the weights moved to the outer limits of their travel.  I have been unable to figure out the purpose of these weights, unless it is to provide some friction against the housing and thereby help to engage the Bendix unit.
(Comment from Peter Mack: I think the fly weights might act as a brake if the bendix remains engaged after the engine starts, forcing the bendix to disengage. They don't obviously fly out when the motor spins no load, so I'm guessing they only come out on an over-rev situation.
Centrifugal weights


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(updated January 12, 2016)