So, while adjusting the carburetor on my paramotor due to the heat-wave we’re experiencing I got a super loud noise and instantly killed the motor. When carefully pulling the pull starter I found that the sprocket of the electric starter didn’t retract all the way and stayed partially in contact with the starter gear on the motor which.. isn’t great.

I pulled the electric starter motor out to have a look and it didn’t look right..

When connecting 12V to the inputs the sprocket was thrown out but instantly retracted half way. When disconnecting the power it didn’t fully retract so something made it stick.

The starter motor is fairly simple to disassemble:

Four screws holding the motor casing and gearbox together and

the brass nut connecting the positive pole to the motor. After removing those the gearbox slides apart easilly.

The problem when the sprocket doesn’t retract is in the bendix gear that’s responsible for keeping the sprocket in contact with the starter gear as long as the electric starter is engaged. Had a look at the bendix gear and there was a wierdly shaped rentention spring partly protruding and some loose parts inside.

To disassemble the bendix gear you need to remove a retaining clip that can be accessed by compressing the internal spring by pushing the rightmost cup downwards.

After removing the retaining clip the entire spring compartment slides off the shaft.

With the spring compartment out of the way the sprocket housing with the weights should rotate right off. Mine didn’t due to minor damages on the shaft so I had to convince it using a puller.

Taking it all apart I saw that the weights that’s supposed to lock the sprocket in the extended position had come loose and one was missing. It must have shattered to be able to escape the housing and in doing so doing some damage to the other components like the retaining spring and bottom containing plate.

At this moment I knew I needed a new starter or at least a new bendix gear. The gear was 66 pounds and 85 pounds shipping at the cheapest place I found it, and the starter is much more expensive than that. Since I’m allergic to shipping costs being higher than the price of the actual product I started looking at options.

First I thought I’d just make a copy of the weights in CAD and make one on the CNC mill, but that’s a lot of work as it is quite a complex part.. Then I started looking online for bendix gears.

It seems the Moster185 starter is similar to the starter used in many KTM bikes and loads of moped motors. I found a place in Sweden selling bendix gears for mopeds that looked similar to the Moster gear and at $19 with shipping I gave it a try.

The moped bendix gear is mostly identical to the Moster one except it’s got a different reduction gear at the leftmost end – and rotates the wrong way. It does however contain all the parts I was missing..

I put the replacement parts into the Moster gear, re-assembled the starter, installed it on the paramotor and it works like new!

I’m certain there are moped bendix gears with the right reduction that goes the right way and thus are identical with the moster gear but I did just order the first and cheapest one I found.

Note: I did try running the starter with 2 and none of the weights installed but it then disengages the gear on the motor as soon as the motor hits TDC, so all three weights are needed for the starter to work properly.