Hello All, This is my first post on this forum and Im opening up with a project that I started just a few months ago. Hopefully I chose the right forum for this build. If not, please feel free moderators to move this where you deem appropriate. The two main reasons for my starting this thread are to: 1. Show our progress in reviving this old endure 2. Seek advice on any possible entanglements Anyways, started working on a 1971 Yamaha AT1 that one of my good friends has had for a little while. Stopped working a few years ago so he decided take it apart to see what all was wrong with it. So now were piecing it back together and running through all of the fundamental diagnostics, troubleshooting, etc to ensure everything is in working order. So far we have the engine mounted (shoved some shanks through the motor mounts) to the bike frame. Kick starter is good to go. Engine seems to have compression although well test it once we put the carb back together. Right now were in the process of re-wiring everythingmost of the pre-existing wires were either frayed or fused together. The wires crimped to the armature (battery/generator according to the manual) assembly seem to be good so well use those and re-wire from there. See pics below. Were currently deciphering through several wiring diagrams so any insight would be appreciated. Thanks and enjoy!
Looks like a pretty good start, way better than the old AT1 I inherited from an old boss, not much of it wasn't completely rusted, bent or broken , Plan with mine is since the engine was basically corroded to nothing is to slap a blaster engine in it "just about any air cooled yamaha 2 stroke interchanges as far as bolting up into the frame". The subframe was badly mangled, forks are toast as are the wheels, so I'm thinking mono-shock with newer disk front end and modern swinger from a ttr-225 or 125 big wheel. Sort of an ultralight cafe smoker for the cart track
After testing compression we were only able to build up to ~80psi. Should at least be over 100 psi. After pulling the head and piston out it has been nothing but doom and gloom. Rust and sand all through the cylinder walls. Piston rings are done. Walls are scored and glazed. Reed valves need to be replaced. Rust on the head collars and studs. I think it's fair to say that someone ran water through this a long time ago and throw some dirt in too. All things considered, this is probably just going to be a basket case of a project. We would need to get a new piston, new piston ring set for sure. A good honing would need to be done too. Probably be better off just getting a new engine since buying OEM parts is nearly impossible. We'll put everything back together and sell it on craigslist as "not running" haha. On the plus side, got in touch with a good friend of mine. He has an engine off of a CT-90 that he gave me for a few hundred to fix up. I'll be posting another thread later this week.
Hey, I've got a similar project, and if you haven't already sold the bike I do have a spare cylinder and head as well as a bunch of parts from my parts bike. If you need them feel free to PM me, I'll let them go cheap for a fellow inmate and some probably free minus the shipping charge.
Just a note, that is not a 1971 AT1 engine, the reed valve (Torque Induction) engines didn't come out until the 1972 model year. My brother and I restored a 1972 CT2 a few years ago, surprising how available most parts are even 40+ years later. One of the best places I found for NOS parts was www.nwvcp.com Good Luck with the restoration....
In 1972, it was called the AT-2 and in 1973, it was called the AT-3. That said, the VIN numbers always said AT1, not matter what year. Also, the VIN year is the year it was manufactured, which in many cases was the year prior to the model year, so a VIN of 1971 was most likely a 1972 model.
