That's good news.
The old alloy corrosion trick.
That one would be up there with the worst i've seen.

Yea it was bad rt and that’s picture is after I ran it through the ultrasonic for an hour. Before that basically the whole thing as covered in white corrosion and orange waxy stuff which I can only assume is deteriorated brake fluid and maybe castor oil lubricant (assembly lube) 

it was basically plugging the whole lower section was gum wish I took a before photo lol 

Some progress. 

new tyres
weny Bridgestone mag mopus g511. 2.75 front and 3.00 rear as delivered here in Australia. 
New wheel bearings and seals. cleaned and repacked Speedo drive. had a bit of trouble installing wheel bearings they were binding up on the hub spacers. I probably should have used a flat bearing installer that evenly compressed inner and outer races rather than just pressed in via the outer race. Will see how that goes 


front brake system is rebuilt but the o ring between master cylinder and body is leaking. I thought it was a 39.7 x 3.5mm o ring Jis p40 but I didn’t measure I just went off another thread. It in fact seems like I need a 42 x 3.5mm o ring. Maybe a 43mm. In epdm. Will try a local shop. Bit annoying 

I ended up buying a new old stock front brake hose too. 

basically will just do some painting of odds and ends and then get into the engine rebuild. 

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I have a youtube channel for anyone interested

I go through how to rebuild the master cylinder and a few progress videos

www.youtube.com/@Graters1989

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Fe updates. Bike is nearly back together. Engine rebuilt. Will do some videos. Few walkthroughs on my YouTube channel feel free to check it out. 

 

Just a question not a criticism but our RX's in NZ had a non squish head, just a gentle curve. Correct piston for ours was completely flat top piston but identical in every other respects. I see yours is a convex top so thought I'd ask that's all. Just thinking if your head is non squish but the shallow curve then a convex piston would shute squeeze some compression up if it cleared the head. I'll watch your video. Got a feeling I've typed this before but maybe not on here. Our RS125 the 4 speed more domestic version had the convex piston & a squish head & I've had both bikes at times & the RX had more torque plus more top end which might be why they ran a 4 speed as had more torque to play with. I worked where we sold & serviced both models back in those great days. I think i mentioned the air boot restriction & I found mine the other day which bought back memories. Thanks for posting about your build.

OK, ignore my waffling in above post. I played the video where ya holding the piston & can see the squish head on the bench so that explains my question sorry.  I'll play the video later with my hearing aids haha as can't quite hear the audio on my phone but I think you're explaining about the squish. All good. Different variations on the same bike for different markets I guess. 

Hey rt 

yea originally flat top piston. The replacement stock Yamaha piston was an rs125 (later model) aka rx125 DX (disc brake) with 5 speed and domed top piston. 

will work perfectly to take advantage of the squish head I have. Although the squish clearance is definitely excessive. Could probably run without a base gasket and just some 518 to reduce squish clearance. Will see how it goes. 

just going to run in stock config. Waiting on exhaust elbow and some fuel hose. I’ve set the timing and have a really excellent blue spark now compared to a weak white one with the old coil and points so I am happy this thing should start and run like a dream from the get go as it’s brand new. 

managed to pick up 4L of siliolene comp 2 plus injector oil for 65 bucks. A lot of people really rate this stuff so I’m excited to use it. I have really disliked oil injection as previously using motul 710 in injector bikes and motorex 2t I was getting too much oil spooge everywhere. 

the siliolene full synthetic has a flash point of 85 degrees which should help complete combustion at low rpm. 

do the old Yamaha pumps oil at 25:1 or 32:1 any idea?

I’ve since converted a couple of my bikes to premix and run maxima 927 for the nostalgia but it does separate so I don’t think I should continue using it. 

I will try motul 710 again. It seemed to smoke way too much in my Yamaha 175. But then the oil pump did fail so maybe it was over oiling. 

a lot of different opinions about appropriate two stroke break in oil. Some say use what you’re going to use if it’s synthetic use that whereas some say mineral for break in to accelerate ring bed in. 

im planning to do hard break in. I know Yamaha originally recommended a mineral with additional 50:1 in the tank during break in. I will probably put some 50-75:1 in the tank and raise the jet needle one notch for break in just until I’m sure the oil pump is doing its job. There will be plenty of assembly lube in the crankcase from the rebuild so that side of things should be ok. 

 

Yamaha pump output varies from ~100:1 at idle speed/closed throttle to ~18:1 at full throttle max rpm.

While some modern oils have components that won't burn at all and contribute to "spooge", jetting is the biggest factor in my experience.  I raced with people using the same oil (premix) at 32:1 or even 50:1 in the same engine that I was running a 16:1 premix.  They had oil dripping from the pipe and mine was clean.  I spent hours and hours jetting to get there though...  and checked jetting every race using relative air density charts and documenting settings at every race.  We raced every weekend so pretty soon I could use the data I had logged to get jetting perfect the first try if conditions changed. 

That said, I wouldn't jet one of these bikes that close...  a little rich is good.