1973 Yamaha CT3 175 rebuild.

On a strange impulse I bought this a couple of weeks ago....




Its an American import, and to my reading of the frame and engine number (CT1 - 120315) it is a CT3 175, circa 1973.
It starts, runs and selects all gears.
But...(there's always a but, isnt there?)
The kickstart flops about and doesnt engage unless you lean the bike to the right. Not ideal.
Most of the bike seems to be in reasonable order, and there are some common parts to the TY's I'm used to working with so I thought I'd investigate further.




Pulling the side case off showed the problem to be a little more serious than I expected.





Finding half of the broken spring clip was easy, but the other half needed some fishing with a magnet. I also dragged out a sizeable lump of casing...





Ho hum. Time to get creative. I pulled the other side case off in readiness for taking the engine out, and found damage there as well.





The U-shaped hole centre screen, above the clutch arm, is not how Mr Yamaha intended. And all the oil spread everywhere is from an ingenious chain oiling idea...





Put the sprocket nut on the wrong way, and you get a constant stream of oil direct to your chain, ingenious!
Not to worry, so far, nothing completely fubar. Yet.





Engine out. The pine needles are from "The big storm", blowing the buggers under my garage door.





And here's the empty frame. Some cleaning up to do while I decide how best to sort out these little problems. Helps that I've just picked up an AT 125 engine, same crankcases, to compare and contrast, and possibly steal from.
Mark

Nice project Mark even if its a little more involved than you'd first thought

So after taking the clutch and kickstart mechanism of, and a thorough clean up, we have this.




The scars and gouges are a result of the broken spring being forced around with the kickstart gear by the previous owner, but they aren't going to be a problem. First thought was to drill and put a nut and bolt through in place of the missing stop, but there are webs at the back of the crankcase which put paid to that idea. There is enough meat to drill and tap it though, so that's what I did. Unfortunately the photo of the drilled and tapped hole was blurred. An M6 allen bolt was carefully screwed in, et voila!



Some liquid gasket to seal the threads seemed like a good idea.



But when I tried the kickstart mechanism there was a slight problem. I hadn't realised the importance of the hole in the casting just to the right of the allen screw. It's where the tang of the kickstart spring clip fits, and without the hole to locate it, it can rotate on the shaft and force the starter gear into the idler gear all the time. So out with the JB weld. I first undid the screw and picked off the liquid gasket, then re- applied it only to the threads in the hole. As I now have a good solid "stop" for the kickstart to return to, I don't have to worry about the shearing force, so I just need to replicate the shape in the casing. As it happens I have a example to work from lying at my feet.......



I carefully pressed a blob of JB weld in place with a screwdriver and built it up to what you can see here. With the idler gear in place, I was able to drop the kickstart in to check I hadn't overfilled, which I had, and carefully remove any excess with a Dremmel. I took a picture, but again it came out blurry. Too concerned about getting dirty paw prints on Denise's Canon.
Back on with the clutch, fitted the seal holder from the AT engine which had been missing, new gasket and bolted it back together. Poured some fresh oil in, and then stood it on end overnight to test the integrity of the seal. No leaks, result!
Replaced the engine in the frame.



Notice it's a lot cleaner now? Not pristine, but cleaner. The shift drum cover was missing, so another piece robbed off the AT. Two of the three bolt holes are damaged, but I was able to get enough purchase on two of them to hold it.
Whilst the carb has been off I've checked that through and cleaned it, then refitted with an NOS connector boot and a new oil pump cable courtesy of Venhill. Switched the clutch actuator arm from the original cover to the AT one and fitted that, along with the magneto cover. Oil tank, petrol tank and seat back on, bled the oil pump through, chucked some fuel in and wheeled her outside.....



After a couple of wary prods on the kickstart, which went without hitch, I switched the fuel on, pulled the choke and crossed my fingers. Second kick was a splutter, third kick and she sprang to life!
Need some daylight and a quiet stretch of road now to see if my theory about the clutch is correct, then I can start on the little things which will probably take months to get done.....
Mark

Lovely Bike. Dublin was full of them in the 70's
All ridden to death sadly.
Always wanted one in my yoof.
Thanks for posting.

Had one

I had one in the 70's and it was a great little bike, crossed rivers over mountains fell off lots, even got chucked over the handlebars. It should cruise at around 55 top speed about 65 on the clock. Went on a rally once it seized, I waited 20 minute it started I drove on no problems. I bought mine in London and drove it back to Holyhead via Bristol turned it into a marathon. Lights are useless do not use in the dark.

Enjoy it for the fun of it.