I had some spare moped money sloshing around and wanted a new and challenging project so I decided to dive into rebuilding a ZA50. There is a good amount of literature on Moped Army and other sites, but there's a decent amount that isn't mentioned so I figured I would add to what's out there for posterity.
First I'll say make sure you have the right tools for the project. There is a good list of tools on the wiki, but there are some that aren't mentioned that you really need to do this right.
- Having a vice set up is going to be a huge help, especially when opening up the second gear shaft to change the pucks. It just makes life easier.
- On the subject of pucks, don't waste your time using too small a screwdriver when you're getting those loctited screws out. I stripped the shit out of my first one and had to grab a second. I picked up a 3/8 in. craftsman slotted screwdriver and it made it way easier.
- An impact wrench was really helpful getting the very first nut off. Remember that it's reverse threaded.
- You need a 15/16 deep socket to remove and properly tighten the big clutch nut. I didn't tighten it enough the first time around and it backed off. That made it so I couldn't roll my bike backwards or engage the starter clutch rolling it forward. Tightened it up right and now its golden.
- Don't mess around with rope tricks or funny business - just get a piston stop. It would have made my life a hole lot easier. If you're rebuilding and don't care about the old stock crank, just disassemble the top end and stick a screwdriver in the con rod. Worked for me.
- Get a three jaw puller or a proper flywheel puller to get the flywheel off. Screw rubber mallets.
- Get a good set of circlip pliers. Or at least a big one and a little one. You'll need a hefty set to get the giant circlip out to remove the bearings on the output shaft.
Other than tools I found helpful, I also picked up a lot of tips from friends and from making many mistakes.
- Rebuild this on a clean table with some white contact paper you can write on. Circle and label each little part and place them in the order they come out. This really helped me keep track of everything.
- Returning to the second gear shaft, avoid holding a blow torch on those screws. If you heat the screws to get them out, you're going to melt the pucks and make an awful gooey mess that really isn't fun to clean up. Put it in a vice with a rag wrapped around the shaft and, using the right size screwdriver, see if you can't brute force them out. If you can't, I have heard and read that an impact driver (NOT an impact wrench - they are different) is useful here. I tried that and broke the impact driver. So. That didn't work too well for me. Like I say above, don't both with too small a screwdriver, you'll just fuck it up. Make sure you use blue loctite when you put those screws back in.
- Heating with a blowtorch did, however, work great for getting the old bearings out of the tranny cover and cases. Just be careful and don't ruin anything.
- On the topic of bearings, I know most people heat the bearings and then drop them on the crank or whatever, but for both the crank bearings and the case bearings, I found an actual press (in this case a ten ton press) was much quicker and safer than messing around with heat and mallets and what not. I messed up the bearings trying to get them into the case with a mallet and heat and had to replace them (again). If you don't have a press, which you probably don't, see if you can't find someone who does. My friend and I replaced every bearing in the engine in about 15 minutes. If you press bearings on the crank, make sure you supply adequate support.
- Continuing on the topic of bearings, if this isn't obvious from some of the rebuild guides, with the crank bearings, press the outer races into the case first, and then press the rest of the bearing on the crank via the inner race.
- The bearings and seals on treats are priced crazy high. I screwed up a couple as well as a couple seals because I am an idiot and took a blow torch to one by accident (woops). I live in Allston and there is a bearing shop - Action Bearing Co. - right up the street for me. I went and checked it out with the dimensions of the seals and the numbers of the bearings and sure enough they had everything in stock. The best part was that for three seals and two bearings, it was only $22. I priced it out and that would have been $55 on treats. So try to find a bearing shop around you and save some cash.
- If you get a sealed bearing, pop out the metal or nylon covers and use compressed air to blow out all of the grease inside there.
- I have since added it to the wiki, but don't forget to get a seal for the output shaft. Its 25X35X7 and it wasn't on there before, so I didn't get one. I was trying to force one of the seals from the seal and bearing party on treats and was really confused about why it wouldn't fit. Then I checked the number on the seal I took out and realized. The seal that comes stock in the engine has a metal ring around it. Pop that dumb thing out - your new seal probably won't have it.
- The seals are kind of a bitch to get in. I used my 15/16 socket to gently tap them in.
- The output shaft is held onto the case by a cuff on the exterior. There is a special Puch tool to pull that bad boy off but where the hell are you gonna get that? Other people have suggested a three jaw puller, but none of my three fit. So I said fuck it and tapped on the shaft with a hammer. It came out with no problem. Way easier than messing around with that other junk.
- On the subject of Puch tools, and this is probably obvious, you don't need them
- When I first bolted my engine together and put it on my bike, my starter clutch wouldn't disengage. I messed around with the adjusters to no avail. I opened up the case and dug down to realize that I had attached the spring wrong. The right side of it hooks into that plastic starter pad thing, that's pretty obvious. The other side rests on the left side of the case. There is a ridge about where it falls. I had mine below the ridge - you want it above, resting on it. I clipped the right side in first, then worked the other side onto the ridge. It's not that difficult. Tap the circular part of the spring down with a socket.
- Those seven bearings on the first gear are not hard to get back in like the wiki disassembly guide makes it seem. I didn't need needle nose pliers or a screwdriver. I just held the bearings and pressed them against the springs and they sat right down like good little children. This is probably obvious to most, but in order to get the bearings to sit, you need to put that nut on first. I didn't understand why they weren't sitting and then did a massive facepalm when I realized my error.
- When you take off that first nut, chances are your bearings will stay in place. Remove the nut and all seven bearings so they don't fall all over the place.
- When I first bolted the crank (I got the $150 aftermarket crank from treats) into the case, it was binding something awful. Wouldn't move nice and smooth at all. This was a problem because obviously it meant I was shimmed too tight or something, but I had no shims in - just the bearings. So I doubled up on case gaskets and it solved the problem. It's now nice and free.
- Be careful when you're case matching. I case matched to a 65 metra, but there isn't as much material as on an e50 and you don't want to cut down all of your sealing surface. Don't forget to grind down that stupid nub. Don't get metal shavings in your bearings. No one likes that.
- If you're using the CDI from treats, the red and white wires plug into the CDI box obvi. The yellow wire connect to both your headlight and taillight. The black wire from the CDI box goes to your killswitch. Send that in one end and ground out the other.
I am sure I am forgetting some stuff and I am also sure some of this is self explanatory or already out there or common knowledge or just me being stupid, but maybe someday someone will find this and it will answer a question they are having. If anyone else has any info, definitely share your knowledge. There really isn't enough literature on this subject and its not as hard as people make it out to be. It is fairly expensive though. Google the shit out of stuff - Adam Augustyn has a great blog with tons of info on ZA rebuilds at http://mustachemachines.blogspot.com/ . Search for shit.