New guy - 1958 ? Mobylette AV78 Help???

I’ve been working on vintage motorcycles and scooters for about 15 years. Mostly Zundapps, some Honda, BMW airheads, etc.

My friend got this moped for free 25 yrs ago —it was getting thrown away I believe. Anyway he asked me to work on a scooter and I ended up coming home from Cleveland to Dayton with the scooter and this moped. Essentially it needs a new top end. The piston was seized and I unseized it gently. The top ring is stuck the bottom is loose I was going to get a new piston kit but I’m so overwhelmed with how many Mobylette models there are I’m not sure which piston to get.

Any advice?

Including some pictures. I am hoping karma comes back to help me because I try to help anyone I can working on stuff in the garage and I’m just out of my league with this moped. I have no knowledge of this beast.

I can tell you it’s a classy beautiful thing though.

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Re: New guy - 1958 ? Mobylette AV78 Help???

Can't solve your parts problem but my compliments on saving a beautifully styled old ped.

Re: New guy - 1958 ? Mobylette AV78 Help???

Any AV/7 cylinder kit should be fine. check out treatlan.tv

Re: New guy - 1958 ? Mobylette AV78 Help???

God bless you!!!!!!

Re: New guy - 1958 ? Mobylette AV78 Help???

One or two heat and cool cycles in an oven will loosen the ring that's stuck...

Re: New guy - 1958 ? Mobylette AV78 Help???

Older round cylinder, if you are doing a restore then get a OEM piston that matches the cylinder, there should be a letter stamped on the deck of the cylinder that corresponds to the bore for a matched set.

If the original piston is not kaput just tired of neglect, clean it up and run it. Need two 39mm x 2mm - FG rings - then gap them to fit proper.

https://www.treatland.tv/50cc-piston-ring-p/ring-39mmx2mm-fg.htm

If you are getting a kit for the bike then get a new bottom end because the earlier AV7 engines do not have a oil journal for the mains and the bearings will not last.

Re: New guy - 1958 ? Mobylette AV78 Help???

Just boil the piston in a pot and let it cool off, repeat a few times til it frees up. Or use a blowtorch. I've done both several times

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