1968 Li125 S

Electric Start??

Let me first say that there is every possibility that this may not work at all. I got this idea after working with my VBA electric start bike and seeing how simple the system was. As I was thinking it over a company called ScootRS in Vietnam came out with a system and it got me motivated to get this project off the ground.


I want to use a standard starter that I know can turn over a 200cc+ engine without too much effort. The PX200 (above) uses a starter with a 90 degree change to a bendix gear that extends off the drive shaft. I took the one off my VBA and tried to place it under the Lambretta crankcase but the design made it stick far too low and I was worried about ground clearance.

Looking through old scooter manuals I found an image of a small frame PK125 electric start which used the same extension gear but was in a direct line with the motor (shown above). I managed to score one off Ebay for only $8.00. Using an existing Vespa motor means if there are ever any problems I can order any of the parts, or a whole new motor without any hassles.


Above is a shot of the extending gear which raises as the motor is turned. It has enough travel to engage with a flywheel mounted ring gear when activated, and then drop down after the engine is turning.


The plan is to cut a hole through the bottom of the mag side flange so that the gear can pass through and engage with a machined ring gear which will be attached to the flywheel. I bought a second mag flange to experiment on so I should be able to get the placement correct. I have also drawn up a diagram of how I think the motor will fit against the mag flange. Click on the diagram below for a 2 page .pdf of the idea. Please note that I have not tried this is just to be used for interest and may not fit like it is shown.


Below are a couple shots of the motor placed in line, but with the mag flange not yet cut to allow the gear through. These shots are of the bottom of the crankcase just in front of the rear wheel. I'll update this page as things come together.


October 2002. I finally had some time to work on this project again, and I took it as far as I can go before welding. I cut a section out of the mag flange and got the starter as close as I could to the flywheel. Unfortunately I'll still need to fabricate a ring gear which has about a 1/2" larger diameter than the flywheel which could create some clearance problems at the top side of the mag flange.

Above is a shot of where the starter motor will be placed. I still need to have a retaining collar with an internal diameter of the starter motor welded onto the mag flange to hold it in place. The space between the bendix gear and the flywheel will be bridged by a larger ring gear. In the picture below you can see how far the ring gear will have to span (blue arrows).

Next, I had to find a way to mount the starter to the mag flange. I found that the starter motor has a 0.5mm shoulder about 1.5cm from the face of the housing, so I needed to find some aluminum tubing with exactly a 63mm inside diameter. I couldn't find anything so I took a 3" diameter rod to a friend who did a beautiful job of machining it down into ring on a lathe (thanks Kyle).

From this point I has able to cut down the length until the tubing depth positioned the gear at the right height in relation to where the ring gear will be on the flywheel.

This is where the collar will be either welded or bolted into position. To get as close to the flywheel as possible, I flattened down the mag housing flywheel wall with a file. I would like to weld this in place, but the inside diameter of the collar is so close to the starter motor shoulder that I am worried the heat may distort the machined diameter. I also fitted the crank and drive side bearing only so I could be exactly sure where the flywheel will sit. Below are to final shots of how the starter motor will sit below the engine casings.

I managed to get my hands on a Vespa flywheel ring gear which I adjusted to fit the Lambretta flywheel diameter. I needed to remove 6 teeth and then have the circle re-welded and bent to a correct circle again. The beauty of using the Vespa gear is that it interfaces beautifully with the starter gear on the motor. Before I cut the teeth out I drafted the gear with 93 teeth (original) and worked my way down to 88 teeth. Each time I cut the new gear out of card and tried it in place to be sure before cutting the original.

I removed the Lambretta fan by drilling the rivets out and was able to locate the cardboard cut out over the existing flywheel base.

Above is a shot of the ring gear placed over the cardboard gear for testing the fit. I now have to make a metal center to the ring gear to mount it to the flywheel. Should be up and working soon.

The final step before building the rest of the motor was to test it out. I replaced the bendix gear to make sure it was a good fit with the ring gear and then fired it up with the help of a 12V-9ah battery that was fully charged. Click to see an AVI movie or Quicktime movie of the starter in action.

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