YZF-R125 flywheel removal

This is just a quick little edit i've put together because I know that at least one of my viewers is about to do the same process, so wanted to show a little what to expect (and see for myself!) what wonderful mysteries line beneath the stator cover etc.
This is working on my "B-motor" which is a motor i got as a non-runner, hoping to just put a new cylinder on and get it in the bike, but then whilst removing the seized wrist/gudeon pin the bearing surface on the little-end got scored, which means now I have to pull the crank out, get the crank separated, fit a new con-rod and then re-assemble. So since i have to split the casings and whatnot I might put a forged con-rod and fresh bearings where I can, though in general this motor is a lot less shagged than my current one .
I'm not looking to do a mega-rebuild on this, just get it back to working, stick a 180cc cylinder and a stage 2 cam on (both of which I have already), and then get it into the bike so I can start work in rebuilding my 'A-motor', which will be getting The Works (with a view to forced induction)...so this is a bit of a trial run.
With a bit of luck this build should see us comfortably into the 90-95mph sorta territory, given we're already knocking on 90's door on the current (very knackered) A-motor.
I've not had one of these motors apart to this extent before so please don't use this as a "how to"-video, it's likely to be more useful as a "here's some mistakes to avoid"-video (like losing the woodruff key, as you'll see), and perhaps might be useful to see what special tools are needed to actually take these beasties apart.
STUFF YOU MAY NEED:
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replacement woodruff key in case you lose it like I did:
www.ebay.co.uk...
[UPDATED - DON'T GET THESE THEY SUCK!] set of box wrenches including an 8mm which should fit in the tight hole indicated in the video (though this is only needed to split the casings):
www.ebay.co.uk...
[EDIT: I just tested them out for filming the next part and they just rounded off right away. Need an 8mm deep socket instead, just ordered one of these: www.ebay.co.uk... ]
cheapo ebay flywheel puller (requires additional bolts in order to be of any use (see below):
www.ebay.co.uk...
Additional/longer bolts needed to make the cheapo ebay flywheel puller work (get 3 of M8 x100mm ):
www.ebay.co.uk...
#YZFR125 #BIKELIFE #BIKEWIFE
Help and support: www.r125forum.com
also in the Discord: / discord

[@zacsibley690]

Glad yours came off so easy I had the same tool and ended up bending the bolts and the tool itself and also mashing you the thread on the end of the crank luckily I had a new crank going in but it took a custom tool being made to get mine out and an impact drill

[@NorthCust]

oh wow that sucks! sorry to hear that. Was it rusted on or something? I could see the main bolt being quite tricky to get off without an impact gun but I thought the wedge/taper-fit should be fairly straightforward (as long as you can break it loose initially that is). How was the rest - replacing the crank etc? I have the same to do and tbh I'm a bit nervous about it tbh... bike engines are very different from mk2 golf engines which is the only crank/deep-engine stuff I've done previously (done a few of those though!). Although there's more bits, at least with the car motors you just unbolt it and apart it comes, and you don't have do deal with the gearbox etc all in the same container :-\

[@zacsibley690]

@@NorthCust it was just seized on with heat I guess no rust, wasn’t easy to come off. The crank was fairly straight forward to replace just pulling it through the crank with the right tool and making sure the bearings are frozen and heat up the outside of where the bearings are going.

[@NorthCust]

@@zacsibley690 did you change the timing gear pulley etc? idk if i'm doing that on this one but the other motor will def need it doing. I guess new crank means new lower gear at least doesn't it?

[@zacsibley690]

@@NorthCust yeah the crank I got came with the new lower gear already installed

[@NorthCust]

@@zacsibley690 right, and did you put a new timing chain and top timing gear on with that or just go with what you had? I'm interested in your experience because I know that like the drive chain, you're supposed to replace them all as a set (timing chain, top gear, bottom gear) but (controversial opinion I know) I also think that is not necessarily always the case, and the people who *insist* that it is are somewhat overlooking how reality doesn't always meet expectations. But the timing chain isn't as easy to experiment with to test stuff like that out as with the drive chain. For example my current motor has a very knackered timing chain and (now that I know I could have changed it when I did the cylinder swap), I think that even if i hadn't replaced the top and bottom timing gear (which i wouldn't really have been able to do), i would still be in a better position now if i'd just slapped the new timing chain on and called it good, rather than spending the last 4000 miles wondering whether my already knackered chain is going to let rip and make piston/valve salad any second.

[@DadDiaries]

Bought the worst R125 as my first bike and am putting the thing back together slowly, dropped the oil today as part of the service while waiting for other parts to find what I now konw to be the woodruff key in the oil pan...well that's another job on the list. Thanks for the video, bikes are a whole new world to me! Just bought the puller, a new key in case this one is damaged and the gasket 👍

[@NorthCust]

Sounds like you've got a bit of a journey ahead of you - if you don't have a copy of the service manual that should definitely help. There's PDF versions to be found online or lmk and I can send you one by email. I suppose what you found in the oil could be *a* woodruff key, may not be *the* woodruff key. e.g. if someone took the flywheel off and the key dropped out like with me but perhaps they didn't find it. Still - not ideal having chunkks of metal floating around your oil, eek! On my other motor after breaking the puller in this video I'm hoping to test with a slightly more substantial one like this: www.ebay.co.uk/itm/403013944769

[@DadDiaries]

@@NorthCust yeah it's turned into quite a journey, I've replaced about 15 cable ties with proper fixings, half the fairings, radiator, headlights, indicator relay, didn't have an air filter...the list goes on and on. The thing did run well though which is a miracle. I got the manual from the R125 forum page is that the one you are referencing? I bought a slightly bigger kit to the one you had but a very similar puller...the update link is certainly a more substational puller for sure!!!

[@NorthCust]

@@DadDiaries I've not seen that many bikes but i had one in for some work recently and i was honestly shocked it ran at all..but it did. They're hardy little bikes ;) that sounds like that's the PDF you need - there's two - the owners manual (less useful) and the service manual (extremely useful). The other puller like in this video just snapped, but not before deforming the end of the crank so I couldn't get the crank nut back on. Lesson learned - put the crank nut back on before you use a puller! :-\

[@DadDiaries]

@@NorthCust thanks for the tip...hopefully it goes well!

[@iKennectz]

Got to undertake this after a cylinder/piston/full gasket replacement as when I took off the engine casing for the final time one of the washers inside got sucked behind the stator plate and is unreachable, thanks for posting as there wasn't much footage on the job before

[@NorthCust]

yeah.. BEWARE! as it turns out i've attempted another flywheel removal since then on my main engine which did NOT go well. I filmed it but haven't got to editing it yet. the stock puller like I have there is garbage, you need one of the round ones with cutouts which are like 12mm thick and you need to put the crank nut back on before you use the puller. I managed to deform the end of my crankshaft and the threads were damaged so i couldn't get the nut back on. I ended up ahving to use an angle grinder to grind down the end of my crankshaft a few mm to basically delete the end thread or so, and then thankfully managed to get the nut back on. There were a few very tense minutes there where I was thinking i was going to have to chuck the engine in the bin, so proceed with extreme caution.

[@iKennectz]

@@NorthCust I think we may have done the same thing. Couldn't get the first nut off without an impact so I called my buddy and he whizzed that off, and we set it up but with only one washer on each bolt where their heads meet the puller, we couldn't budge the flywheel at all with both of us pushing down on a long ass breaker bar, he gave it a quick shot with the impact and may have moved it a fraction but the washers all split and the pully moved instead, now can't get the bolt back on as I didn't read this before having a go. Luckily the thread doesn't look very bad and just the very tip won't let the bolt go on at the minute so now have to work that back on before giving it another shot. In hindsight, should have done as suggested and put the bolt back on before trying to pull and layered up a few washers because it was a lot tighter than expected

[@NorthCust]

@@iKennectz right that sounds exactly liek the situation I had. did you even get the flywheel off in the end? I abandoned in the and and put it all back together, pretend it never happened lol. But yes it was jsut the last couple of rungs of thread which god damaged so I very, very carefully used an angle grinder with a flap disk (which is a bit more gentle, espeically if you slip) and sorta tried to evenly cut the threads back a ring or so. then very very carefully reattached the nut, but there was some gentle adjusting of threads etc. I did think it was egame over but so far she's running fine. thankfully

[@officialmysteriousrider130]

Them tools should come with like a pointed end to stop you mashing the thread's up.i made my own 3way puller & just used the end of a plum bob so it fit perfectly into the shaft that way you wont flattering the end of the crankshaft

[@NorthCust]

key thing seems to be to put the nut back on before you use the puller. I think the other tool I used had a pointed end but that also deformed the end of the crank and splayed it out ('mushroomed' it)...Having the nut on may not have prevented that but at least the nut would be on so I wouldn't have had to grind the end of the crank down an re-file the threads to get the nut back on.

[@davidfont1101]

Hi, one question, i really need help. Do you think its possible to change the timing chain of sprocket without doing all these? just with the hand from the up site? (with the water-pump disassembled) One time i saw my mechanic doing it on this bike, but i dont know how he did it, but because of the sound we where noticing the chain of changing of sprocket.

[@NorthCust]

whilst you can definitely change the timing chain without taking the head + cylinder off, I don't *think* it's possible to change it without taking the flywheel off. I suspect the lower timing chain guide might get in the way and it's pretty tight back there. See here for an exploded diagram which might give you a bit more info: www.motorcyclespareparts.eu/en/yamaha-parts/2008-yzf-r125-motorcycles/camshaft-chain

[@BigBoyPants]

Just changed my flywheel now it maked a awful clunk and grind noise, when it does start the revs are all over the place.. What can this be?? Is the timing out now? Woodruff key was put back in and flywheel lined up with it

[@NorthCust]

eek that doesn't sound good. tbh I don't think I know enough about that area to speculate on what's going on there, especially without hearing the bike. Have you had the cover off to look and see if anything's rubbing? if the woodruff key is in then the flywheel has to be on the right way up, surely but there's any number of different things which could get problematic in that area..

[@BigBoyPants]

@@NorthCust turns out the flywheel i put on had different TDC markings on it and was throwing out the timing, crazy what 2 little marks can do 😅

[@wisterixbrat6947]

You learned to wheelie up in first gear?

[@NorthCust]

em yeah I believe I did on the R125...i think i was on a 13t sprocket and she was still 125cc at the time. so needed quite a bit of rpms too (for clutch ups). bounce method might be less wear and tear in hindsight. I also wouldn't really claim that I 'can wheelie yet'..still very much a beginner. I think normally ppl learn to wheelie in 2nd but that's probably on more powerful bikes. Wasn't happengin on mine ;) Here's a playlist of R125 (and a CBR 125) wheelies from people who are much better at it: kzbin.info/aero/PLFlbA6WoZEkr0l-6YImFio6s4xjUO9Dwx

[@yugimaster22ok94]

What year is this anyone know?

[@yugimaster22ok94]

need to do my timing chain and such just trying to go in with the best plan possible

[@NorthCust]

the bike is a 2008 (generation 1)