The NC23 has been making this ticking sound when first started when cold since I got it. It disappears after a minute or so. This might just be a bad exhaust gasket. It’s also clear the clutch bearing is going, because pulling the clutch in when cold often results in some quite unpleasant noises. That shouldn’t be a big deal, though.

However, lately it’s started making a much worse-sounding, loud rattle around 3000RPM. This also goes away, or at least becomes much less noticeable, when the bike has warmed up properly. The sound is what I associate with piston slap, but I’m not sure what it is. It’s confined to a very narrow RPM range, it’s basically only there between 3000-3500 RPM. It largely goes away when the bike has warmed up properly.

I tried recording the noise with my phone, but its microphone isn’t good enough to pick it up. I finally pulled out the Macbook with the high-quality Sennheiser USB microphone, which worked much better:

Any ideas what this might be? I first noticed it about a month ago and it got worse quite rapidly. Now it seems to have stabilized.

There’s also a low-end rumble that I assume are the crankshaft or rod end bearings. I’d be fine rebuilding the engine and replacing the bearings, but I don’t want to do that until the NC30 is regularly rideable (and who knows how long that’ll take) so I hope it can go a little while longer.