He guys 

been a while since I’ve been on the forums bbut I bought a 79 rx125 single. 

sorry if I’ve posted in the wrong area. 

does anyone have a parts manual and a service manual for this bike? 

pretty tidy and original looks complete. Will leave it stock. Engine probably needs a rebuild 

Front brake caliper and master will need a rebuild. 

I’ll probably put a flatslide on this bike. Upgrade the reeds and build a stainless expansion chamber. Might recut the cylinder head squish too. That should give it a bit more pep 

  

 

Had a few of those & also had a couple of the 4 speed RS125 & the RS had better porting & a squish head & was a Rocket. Revved high & had better torque than the RX. Also RX had an annoying gearbox ratio spacing with stupid gaps then super close 4th to 5th. One RX i had, had a bridged inlet port or maybe they all did but not the RS. Im in NZ so we got bike for Oceania so might've been different for other parts of the world. I descovered on one of my RX's --well they would all have--a noise baffle in the inlet boot at the airbox fitting. I'll find a pic somewhere. I removed mine & sure helped it breath. Also in more recent time-- 20 or 30 years later--i was given two RX's--or was one an RS, cant remember--but i'll see if i can find my pics which'll have you scratching your head for sure haha. What we do for fun. I worked in the local Yamy shop in those great times. I'll see what i can find. Just remembering back "reminiscing--i fitted a 175 top end on one which worked great. Not sure now but i probably had to make a base plate but can't be sure was long ago. RX has a tall piston from the pin to the top & cylinder is taller too to match. I used an AG175 top end which has restricted farm bike porting but idealy a CT2 or CT3 cylinder would go much better or even a "74 DT175 that has the same 4 long studs with deep sleeve nuts whatever ya call them holding it all down.
I'll go find my pics & videos--mission impossible maybe. Ok useless video but!! cant find my pics.
Ok preceeding the video, this went on. Pretty much the same on two free RX's i was given. Rusted corroded solid. Both ran well in the end & not a cent was spent haha. photos.app.goo.gl/mdnk1Ht2j5J7wtxi8

Hey rt glad to see you’re still around 

thanks heaps. Be interesting to see the differences in porting between rs and rx125. 

I just saw a video on YouTube with a rx125 with a yz cylinder and head and a 34mm flat slide now that sounds fun

 

Haha yeah YZ cylinder would set it alight for sure.

Found service manuals on ebay. Had to bound the url in asterisks to get this to post. There's a trick to get it to post, but I forgot what it was. *https://www.ebay.com/itm/384934846139*

I usually try and avoid the eBay manuals as usually they are vultured from forum Tech libraries and non enthusiast people profit from copyright infringement. I don’t tend to like supporting that. 

free sharing of classic material is far less offensive to me. Hence why I asked here first. 

yamaha Australia can probably email me a parts manual I’ll see. 

service manual would be nice  


 

 

RX front brake caliper used to seize up--rust up--in how it moves on its mount.
Bit of an unusual way of doing things but was effective none the less.
Also the Seal swells in where the piston runs & doesn't like returning.
But wait--there's more lol.
& the mastercylinder piston cup swells until it fails to clear the pin hole that lets the pressure off when releasing the lever.
I guess that's normal faults for any hydraulic brake thats many years old.

Just googling & this showed up so out of curiosity i dragged it along--not played it so-far so maybe he's aware.
But--the RX has a non squish head & a dead flat top piston.
I see looking closely that his piston is fractionaly dome topped which makes it an RS piston--identical but!!
Be interested to see if there's enough clearance to the head & if so--how it ran with very high compression. Ok i'll have to play the video now.
Also note to self, find my inlet noise baffle i removed for a pic to post.
Watch the video. Sounds realy good, with the chamber exhaust & 28mm RD carb.

rt that seems to be exactly what’s happened. 

front master and caliper need rebuilding. The caliper piston is so heavily seized I’ll have to use the grease gun method to drive the piston out. Thankfully can obtain all new brake pads caliper and piston and master kit from yambits. 

I’ll  need new sprockets and chain 
new crank seals and gearbox bearings 
new tyres 
new air filter. Will keep stock airbox for now. 


have been washing parts. Bought some of the crc smartwasher non toxic non caustic solvent free parts washer fluid and stuff is coming up like new. 
 

Well ordered a heap of rebuild parts from yambits 

able to get new caliper piston and seals 
also master cylinder seals and piston 

needs wheel bearings new tyres. New crank seals. Replacing both front brake pads and rear brake shoes. 

replacing stock reeds with composite ones from yambits. 

new chain and sprockets. Have ordered new piston rings will probably just hone the bore and run the existing piston. 

picked up a spare rx125 cylinder to port. 

it has the bridged inlet port with a boost port. I will widen the boost port,  exhaust port needs mild widening, also some big casting dags to clean up. It does have squish head but clearance is pretty wild. I might try and match the later Yamaha rxz135 potting as that makes 18hp stock without expansion chamber and a 28mm carb. I’ve seen some dyno charts of rxz135 with properly designed expansion chamber making 25hp. 

im wondering if 1980 yz125 cylinder will fit. Bore and stroke are the same but I think yz125 reed inlet housing is bigger. 

will put a 28mm flat slide on. 

wanting to get 18-20hp minimum. Hopefully more with a properly designed pipe 


are photos not working on the forum?