I've actually fitted 2021 model engine into 2014 CBR125R which has same engine as 2019 CB125R. It took me some work adapting it into to the CBR wiring and ECU but I got it running, not 100% perfect though. From my experience I can tell you that older engine will definitely not fit into 2021 wiring and ECU. Some crucial parts have changed like alternator is 2 wire instead of 3 wire, CKP sensor is 3 wire hall effect type while old engines have 2 wire induction ones, flywheel is different because of the sensor as well. To make old engine to fire up you would have to switch flywheel (which does fit between models) but you have no way of fitting the hall effect sensor in old crank case cover. The way I got the 2021 engine to work with CBR125R is I've try tested over 20 different 2 wire induction sensors and 1 thankfully works from some Hyundai/Kia even though it has 800 Ohms instead of 100 Ohms. Well in any case you can fit the engine in the frame but you will also need entire wiring loom with ECU from older model as well as throttle body. Also new engine has very slightly changed stroke length and piston size so I think that's why my CBR doesn't run as perfect as should be. Timing is a bit off.
@@sh4nxy63 Physically it will most likely fit if there is front engine mount compatible from 2021+ to your frame as the starter and mount positions are moved. To get it to run though you would need to do same things I did most likely. I would not recommend, better to get JC79 engine. Also different exhaust as the exhaust port is at different position. Throttle body need to be from 2021+ as well as its screwed on.
@@sh4nxy63 some water hoses not gonna fit, 2021+ has 2 pin temperature sensor screwed in the cylinder head, older one has 3 pin in the thermostat housing, newer one has no temperature indicator on the instrument cluster. Full wiring and ECU may work but not sure with how it will work with ABS, honestly not worth converting to newer engine, its barely any better, first gear is very long so forget wheelies, central spark plug is harder to get to if needed.
Do you know why it didn't qualify for a warranty repair? I'm not a fan of K&N filters. I had one on a pickup. Fine dust mixed with the filter oil making an abrasive goo that got sucked in to the airflow sensor and throttle body.
