It banged it up pretty well but it still looks like it could be saved with judicious use of a good sealer/gasket maker.
Since it ran for 3yrs you might have a worn crank seal. If it is leaking the cylinder wont charge as the mixture escapes at the seal. A quick check for crankcase loss is a squirt of fuel in to the carb. If it doesn't run then. Shoot a squirt into the cylinder directly(spark plug) if it runs then its more than likely a leak in the case area( gaskets or seals). This is assuming compression and properly timed spark.
The Solex parts interchange for the most part if not individually in assemblies. I rebuilt the engine for my 1974 Velosolex project using NOS Hungarian parts. The removed used stuff was still pretty good so I built an engine using a Hongdu bottom end with the rest Solex. Was a good runner.
I think I still have a box of engine parts. Let me know if you need something and I will dig through the attic.
Thanks Cannonball. This is one of those times when I'm going to have to think about what to do next for awhile. I'm not even sure I can free the crank. Maybe if I dismantle the rest of the engine, but I need to get the flywheel puller first for that.
As for troubleshooting the non running condition, I never got a chance to try anything before it seized, but before taking down the top end I did try fuel into the carb and plug hole with no joy. I was thinking maybe the compression was just low enough not to start and the new gaskets would help but it didn't seem like it was going to fire.
You mentioned properly timed spark...ours have a cdi don't they? All the literature I have on Solex engine is for points ignitions. I thought I had read somewhere that as long as the flywheel was on correctly the timing would be right for a cdi. If I'm wrong about that, maybe that is my problem.