Z250SL chain and front sprocket replacement

Here we have an original fitment RK KRO520 O ring chain, knackered after 4500 miles. The previous owner (up to 3200 miles) never sprayed or tensioned it, but to me this is still a very disappointing lifespan. As you can see, the adjusters are way back - this is stretched, I'm not replacing it for fun (as if!). It was actually starting to stretch at such an alarming rate that breakage was threatened, I had to have a cup of tea and lazily spring into action..

Bring on the special tools!

Grindy grindy..

Bit more, show it who's boss.. Ping, off comes the (burning hot!) plate.

I expected the chain to be bendier than it was, given how much it had stretched. The sprocket is whizzed off with an electric rattle gun, a great piece of kit.

The front sprocket was also quite hooked, again very disappointing for OE at 4500 miles!

Thankfully Kawasaki had the sense to fit a large rear sprocket with loads of teeth, so that still looks brand new. On goes a new front sprocket, a Techcorps 151214 that is actually meant for an Estrella and has a slightly wrong offset but everyone is selling them as fitting 250SLs and 300s, and a JT Z3 520 chain because I've seen precisely zero reports on how good they are.

The torque spec for the front sprocket nut on the the old (post 2008) Ninja 250 is 127Nm with the lot covered in a moly oil, oil and moly grease in a ratio of 10:1. I didn't bother with that, the threads weren't that clean anyway. I got up to about 90Nm and gave up, the bent washer will surely hold it in place just fine. And yes the bike is leant against a car, it deserves it for not having a centre stand.

At the time of writing the bike has done a further 2900 miles and the JT Z3 chain, despite rusting almost straight away in the extra salty conditions of the winter of 2017/18, has been quite the delight. Mine was £45 off ebay and I would put it in the same league as a midrange DID, and far ahead of the RK it replaced. The side plates are also reassuringly thick, it is a world away from the old, cheap and flimsy JT chain that adorns the CBX250. They have really put a lot of effort into this new Z3 range. The Techcorps sprocket, on the other hand, is not doing very well with quite pronounced hooking already. With this setup, occasionally slathered in gear oil, I need to tighten the chain every 800 miles or so which can be extended to ~1200 if needed. This is likely mostly down to the sprocket wearing, but also a comment of how snatchy the 250SL is, how rubbish the gearbox is and possibly how heavy it is on chains and sprockets - certainly the thumpers of old were known to chew through chains, and they weren't running anything like 11.3:1 compression ratios!

I've gone right off RK chains though. Have you seen the price..??