Yamaha SR 125 - putting an old bike back on the road

You need an impact driver to remove those screws - if the heads are really chewed up it is sometimes possible to remove them with a small cold chisel - apply the chisel to the side of the head and tap it so that it unscrews. Or you can cut a slot in the head with a dremel or something similar. Heat and penetrating oil also helps. Also, a 50/50 mix of acetone and ATF is a good penetrant - apply and leave for a day or so. Anyway, it's a good plan to replace all philips screws with cap head screws. Makes it a lot easier when you come to take it apart again.

No need to guess the chain slack mate, if you hold a taper measure on the rear of the frame the chain should fall within 5.5cm and 7.5cm on the tape measure , Just measured the usable range window on my guard for you , just flung a chain guard as well cause it was cracked and replaced it coulda had it if id known you needed one lol >.<

Thanks a lot mate for taking the measurements for me. I didn't know when I saw the manual whether the usable gap was on the upper or lower part of the chain. As I said before, the slack I was worried about was on the top half of it.

Here is a video that shows my chain. General opinions are welcome too.

The sprockets seem fine. Some of the links have some surface rust, but I feel to play. The O rings all turn freely.

The upper half is slacky a bit and it touches a plastic part in the front, I don't know what it is but looks like it might be a guide of some sort?

When it's on and the gear is engaged I feel more play than I would like to see, but then again I'm not that experienced with MC's. What do you guys think? See what happens when I engage the gears here:

By the way, I was able to loosen the axel nut with an adjustable wrench. I only tightened the chain adjustment by one dot. I noticed that on the right hand side, the metal protrusion that the chain adjuster pushes against is slightly damaged. I didn't do much more as so keep everything in place. The videos above are after whatever I did.

That looks slack to me mate maybe try another notch shouldn't be catching the plastic.

When I get home I'll take a vid of mine so you can see how it compares.

You say one side is damaged , is it affecting the level of the wheel and are both sides on the same number?

It's held in place but the protrusion is "worn out" so holding on about a 1mm thickness on the right side.

I've tensioned it one more notch and it looks a tad better for now. I think I want to do one more notch, but that's as far as I could pull it by hand. Should it be able to go all the way up to, say, 7? The axel doesn't seem to want to go any further back.

ive got mine right on 9 but my chains about ready to be replaced, on its last legs lol you can see mine sits just above the plastic by about 5mm

it has enough to play to push it down to the plastic though.

hope that helps .

.

I clean and lube it every month and as i said its knackered, getting replaced payday

.

there ya go took the pic down seems its so upsetting to you i was just trying to help someone more fool me.

What just happened, I missed something? If there's anything useful I would like to see it, and guys please, this whole forum is for members to share the experience of something they love.

I tightened it to where I wanted, that extra notch, but turned out that was way too tight. See here:

Notice the wheel jumping. When on neutral it hardly turns.

So I backed off that one notch and left it here where it seems ideal. It is still touching that plastic though. What is that plastic? Is it supposed to be there? Maybe the plastic is off.

Here's the final adjustment:

You're better running the chain slack than tight. It should be 35/55mm movement in the middle of the lower run. The plastic on top is to prevent swingarm damage when the top run is slack as you slow down.

And you need to get that front cover off so that you can get a good look at the front sprocket - I'm fairly sure that it will be knackered. As I said before, you'll need an impact driver and cut a new slot in the screw head with a dremel or something similar. If you find excessive tight spots in Chain after adjustment, also indicates chain wear. Use 50/50 mixture ATF/acetone as a penetrative release agent on the screws, WD40 doesn't cut the mustard. Leave at least overnight to soak in.

And that chain still looks a bit tight. If you overtension the chain, you will destroy the gearbox output shaft bearings. Not good.

All great advice, thank you so much!

I had not looked for prolongued period of time at the chain when I first got the bike, but after cleaning it up it felt like the slack was getting very jumpy on the top half of the chain. That was worrying as it looked like it could jump out of the sprockets any minute.

I guess the next job should be to access the front sprocket.

[mention]megawatt[/mention] so it is normal for the chain to be in contact with the plastic like that?

[mention]Speedy23[/mention] by ATF, do you mean Automatic Transmission Fluid? Sound like it's supposed to act like a medium for the acetone; will anything else work? I have brake fluid at my disposal. e_e

I've waited a couple days with WD40 now, and as you said, it doesn't cut it.

Hi again - yes, ATF is automatic transmission fluid. It's the acetone that acts as a carrier for the ATF, actually. When you mix it up, it will go cloudy, similar to oil/water. Don't worry - it's supposed to look like that. Or you could use plus-gas but I reckon the acetone/atf works better. Dunno about the brake fluid - that's very hygroscopic (absorbs water) and it will bugger the paintwork up. But that cover must come off.

I wouldn't say normal. But they put it there because it can happen. In my opinion you need a new chain and sprockets, then maybe it won't touch the plastic.

I'm in! It was a tough battle against those screws but I won! I cracked the thing open and got inside. I used brute force, and those screws look ugly as hell, inside, and now outside too.

To be honest the sprockets look good to me. What do you guys think? There's hardly any wear other than paint on the rear sprockets. I have new sprocket/chain set that I was given with the bike when I bought it. The chain is sealed, the sprocket were probably retrieved from a bike since the smaller one is rusty. But the teeth look the same on mine as they do on the unused ones!

So I've given everything a very good clean up. I've never been greasier or grimier in my life. And when everything was back in, I gave my chain some chain lube (that thing becomes very sticky! sorry, I have to touch).

The chain decided to go back to being a bit jumpy (as if it's too tight) even though it's the same setting as yesterday's. By jumpy, I mean where it feels as if the drive is getting hiccups.

I was also looking at the rear wheel alignment. I don't remember the rear wheel having that 1-2mm off-centre feel to it. Look at this video and try to see the circle of the wheel relative to another static object. I tried to capture it. It's as if the wheel is turning off-centre. I did not notice this before, but maybe it was there and I just never saw it.

On an irrelevant sad note: I FINALLY got the sound of my Speedfight 2 controlled enough to go to MOT (or be sold). I turned it off. Put the SR125 chain together. Went back to start that thing up, and it wouldn't start. Now I might go and make a thread about it, but it may just be the carb, fingers crossed.

Is the run-out at the rim or is the tyre just misaligned? Might just need deflating, tread the bead off the rim and reflate it so that it pops back onto the rim. A bit of washing-up liquid can help here..... (yes, I know, but has he got access to proper tyre lube?)....and invest in a set of cap screws and Allen keys.....money well spent....

I'm thinking the wheel might be slightly misaligned. I think observing the wheel sprocket gives a similar effect. I've triple-checked that both the cam-adjusters are exactly where they should be, but then again, that damage to the right metal notch might mean I have to adjust differently. I'll be back on it tomorrow.

So far, the right fork seal seems Okay after a bit of a clean. I'm hoping to keep it as it is and pass MOT without having to remove the forks. My next option up is gaiters is I have to, but both dust caps are cracked on the sides so I'm not really liking that sight.

What does that leave?

..

Where did I put that list of things to do?

By the way I need a headlight bulb as the dipped beam filament is blown. Do I only get the pear-like bulbs for my bike, or do I get the cylindrical ones? there are some of those listed as SR125 bulbs but I'm not sure due to socket type.

I'm thinking the wheel might be slightly misaligned. I think observing the wheel sprocket gives a similar effect. I've triple-checked that both the cam-adjusters are exactly where they should be, but then again, that damage to the right metal notch might mean I have to adjust differently. I'll be back on it tomorrow.

So far, the right fork seal seems Okay after a bit of a clean. I'm hoping to keep it as it is and pass MOT without having to remove the forks. My next option up is gaiters is I have to, but both dust caps are cracked on the sides so I'm not really liking that sight.

What does that leave?

..

Where did I put that list of things to do?

By the way I need a headlight bulb as the dipped beam filament is blown. Do I only get the pear-like bulbs for my bike, or do I get the cylindrical ones? there are some of those listed as SR125 bulbs but I'm not sure due to socket type.

Get the wheel out and check for run-out in a set of V-blocks or take to to a shop where they can test the rim for alignment. Are the wheel bearings OK? Do the spokes all sound the same if you "ping" them with a screwdriver? You can find loose ones like this that can affect the trueness of the wheel. Take the old bulbs to the shop (Halfrauds?) and they will tell you the correct type (or just put a picture on here....)

I was watching videos of everything until I reached this guy removing his rear wheel, and it just occurred to me that maybe I should also check the axel for straightness? *gulp*

I think I saw a slightly bent spoke on this bike somewhere. I don't remember where. I will check again tomorrow when it's day time. Taking this to any shops is not an option, I'm doing everything at home until this girl is out on the road.

The wheel bearings are surely fine. The top 2 possibilities so far are either misalignment (which is likely because I observed something on the sprocket wheel), or as you said, if any spokes are off.

I'll let you know.

The Speedfight problem is a carb that needs a very good service. I've pulled it out (without removing most of the pipes), pulled the throttle needle out, jerked it back in, let some petrol drop, put it back in, and the bike started... for a short time, then it turned off again and stayed off. At least I know it's the carb.

I may or may not have time to look at the tRusty Aubergine today.

Why assume the wheel bearings are OK? Don't assume anything! Check em, it's not difficult.

Why assume the wheel bearings are OK? Don't assume anything! Check em, it's not difficult.

Because I had already checked them earlier and again and again? I did it by grabbing the wheel and pulling it up and wiggling it around. There was absolutely no play whatsoever.

The swing arm plays upwards a couple millimeters but that's definitely the swing arm.