jbcollier wrote:Get a caliper and measure the diameter of the flywheel thread and the diameter of the "valleys" of the extractor thread. They should be close with the extractor thread being a bit smaller.
I have a had a few poorly made extractor tools where the starter thread was not formed properly. A touch up with a small file fixed it.
If anyone has used a hammer to try and "shock" the flywheel off, they may have damaged the threads. See if you can feel or see any damage or peening. You may be able to CAREFULLY grind down the damaged threads with a dremel so the extractor can reach the good threads.
Thanks JB: I bought a new one from Cambridge Lambretta and it went on perfectly, treaded correctly with a bit of elbow grease needed to get it in.