Since the “A-motor” has been removed from the bike now, I need to strip the upgraded clutch I built a while back off it, since the newly rebuilt “B-motor” is already slipping on the stock clutch and the upgraded one needs transferring to that engine when I do the “end of break-in miles” oil change.
Continue reading YZF-R125 R15 Clutch upgrade – 6000 miles inspection and stock clutch install speedrun
The B-motor runs!!
woop! it runs \o/ (so far).
This has been a massive learning curve for me, particularly the sheer number of operations which have to be completed, as well as having to build at least 2 special tools to get the job done meant (for me anyway) it wasn’t really possible to “see” the whole process from start to finish, which in turn makes me very nervous on a project.
Continue reading The B-motor runs!!YZF R125 180cc kit top speed
TL;DR: Top speed I’ve managed (so far) on my gen1 with 180cc kit, 160cc injector and longer duration cam, with PCV + Autotune/wideband: 89mph at which point we’re still on power but bouncing off the rev limiter.
UPDATE (4/8/2024): I’ve just increased the RPM limiter from 10.1k (standard, according to the ECU itself, not hearsay) to 11k, which should give us a new top speed of 96mph – I’m awaiting an opportunity to test this as with the rebuilt 180cc engine with the rebalanced internals (forged con-rod and lightened crank pin) she’s still very much in the power band at the previous RPM limit of 10.1K. At the time of writing this i’ve only ridden it once with the new limit and it was only locally but she pulled all the way to 11k so I’m hoping we can get close to the theoretical 96mph. I’m gradually getting a bit more set up in my new location and this is something I’m going to be working on in coming weeks/months, so watch this space, and my youtube channel for updates. I think with a little more work 100mph will be possible.
Please note: just raising your RPM limit may not be wise and may destroy your engine, especially on a 180cc kit since it changes the engine’s internal balance factor. I’m doing it here because I’ve built this engine a certain way which means the power band actually comes in a little higher than stock, so when we were hitting the limiter before we were still very much in the power band, and the engine wasn’t shaking or sounding unhappy, in fact it was smooth and in “mechanical harmony” (best way I can describe it). You can probably go a little higher on a stock engine (e.g. 500rpm) but mine is most definitely not a stock engine, so don’t try this at home kids, unless you know what you’re doing.
So I’ve noticed there’s people searching on this topic so I’ll share what I’ve discovered so far, hopefully it’s of some use.
Top speed on mine when I got it, as 125cc on stock 14t sprocket was 83mph (indicated). That was absolutely throwing-it-down-a-hill-with-the-wind-behind-you, the most I could get out of it. 83 seems to be a fairly common top speed for stock bikes. Some other people have claimed 86 out of a stock bike but I can’t verify that myself and that wasn’t my experience and speedo variations could account for the difference.
Continue reading YZF R125 180cc kit top speedYZF-R125 180cc “B-motor” engine build photo catchup
I started a thread on the forums a little while ago but meant to mirror it here. I may add in the old posts here if i get time but otherwise this will have to serve as a little photo-catchup. please refer to the forum thread for the full story. I’ll try and update both moving forwards..
Whilst not pictured here the cylinder and head are loosely on now while I set up the timing chain etc. Hopefully in the next few days it should be ready to fit.
[EDIT: pics updated, engine fitted and runs!]
Splitting the crankshaft on YZF-R125
Biting the bullet here and using the ebay hydraulic pless to separate the halves of the crankshaft and replace the con-rod etc. This is getting serious now..
Finding crankshaft balance factor on YZF-R125
going further down the crankshaft-rebuild rabbit-hole and getting on with the crankshaft rebuild for my new motor…
In this video we’re looking at trying to calculate the balance factor for the old 125cc setup vs with the big-bore kit, to see if that maybe explains why it’s run a little differently since going big-bore.
The logic is based on this video from 2StrokeStuffing (thank you!): https://www.youtube.com/watch?v=0hoE_…
splitting the B-Motor crankshaft on YZF-R125
B-motor crankshaft rebuild progress in pictures…
what we’re starting with..
Replacing inner cam bearing on YZF-R125
This is me attempting to replace the inner camshaft bearing on a YZF-R125 cylinder head.
I’ve not done this process before and it involves extracting a bearing from a blind hole. I’ve found how it’s meant to be done but this is a test to see how well that goes to see how difficult it is, and to help me decide whether it’s something I want to try doing on my main engine.
The bearing puller I’m using is pretty much the default ebay one, just search on “blind bearing puller”.
Removing lower timing gear on YZF-R125 attempt #2 – success!
This is the second attempt at removing the lower timing gear and the captive bearing on the crankshaft of my spare “B-motor”, which I’m trying to build up for my bike.
Idk if this is how it’s supposed to be done but I’m working with what I’ve got.
Whether this turns out to be a good approach or not long term remains to be seen but for now let’s see how far we get with it…
How not to remove lower timing gear on YZF-R125
This is the first of my “descent into madness” series of videos where I’m trying to rebuild this spare R125 engine.
I bought the engine as broken and when I took the cylinder off the bearing surface of the little end was damaged, which means the crank needs to be pressed apart to fit a new connecting rod.
So basically I have to take the entire engine completely apart just to get to this one dumb piece to replace it.
The videos are out of sequence but I have such a backlog and there was going to be a plan and it all went to crap. Every expert I was hoping to get to help me with this basically just disappeared or didn’t follow through, so I’ve finally resolved to buying the kit and figuring out how to do it myself.
Even though the engine in my bike has issues (from when I messed up a couple of years ago), despite that it’s done another 5k on the 180 cylinder (even wiht the timing chain issues) and I have not gone easy on it 😉
I’ve had a few people asking me to rebuild engines and do upgrades etc which is very cool, so it seems like it’ll be worth learning how to do it.
Hopefully this all ends with an engine dyno and building mad engines as was always the dream/plan 🙂 I’ve added this video to a new playlist for the B-motor rebuild so I can add all the other videos to it as I work through them. Thanks for watching and thanks to SXparts.com for sourcing hard-to-find components like the lower timing gear.
UPDATE: I said in the video (at 2:08) the lower timing gear wasn’t available, well it turns out i was wrong on that and you can get it here. Thanks to A for the link 🙂 https://www.cmsnl.com/products/sprock…
