Just fitted a new hope 30 t on the front and a sun race mx3 on the back along with a new kmc chain. Anyway in top or bottom gear when putting pressure down it sounds like the chain jumps every 2nd or 3rd pedal stroke. I’ve inspected the chain and teeth but all appears in good order, any clues?

Check the alignment of the jockey wheels – you may need to tweak the limit screw to get them to sit directly in line underneath.

Mine did this for a bit though (Also KMC chain on MX3), and either the limit screw thing sorted it out or (more likely) it just wore in a bit and decided to stop doing it.

What mech are you using? HAve you got the mech completely clear of the cassette when in the largest cog?

Hi, it’s a SLX mech and b screw wound in gives clearance, odd thing is it only does it in top and bottom gear. I have the same set up on my hard tail and that’s fine.

are all the components new?

have you checked the chain for a stiff link?

Could be a worn cassette if that’s not new too.

In my experience its usually the cassette that’s worn, especially if the old chain was pretty worn too. Does it do it in all gears?

All brand new.

+1 for a stiff link

APF

I had a similar problem with a new KMC chain. The joining link wouldn’t sit on the ring properly. Seems to have worn together now though.

If you’ve changed all that I would of done jockey wheels as well

If it’s skipping every few pedal revolutions then it sounds like a chain issue.
Did you take any links out if the chain before fitting it? May just be a stiff link.
Try bending the links sideways in your hand to loosen them up.
Also check the quick link is locked together properly.
I’ve heard of KMC chains rarely causing problems like this, but it seems to go away once they’re worn in a bit.
I always get KMC chains but have never had any problems

Just checked the chain and no stiff links but the joining link looks slightly wider than the rest and could possibly be getting caught between chainring and spider.

Could be the chainring…… I had to ditch my hope one. I could never get it to work correctly – I always assumed that would be the straightforward bit with Hope quality etc. I bought a Raceface N/W in desperation and it sorted it all out straight away. Do you have a spare chainring to put on to check?

Yes a Part worn Raceface N/W. Just curious now as to what’s causing it but will try the RF one or grind a tad off the spider where the chain might be getting caught.

…the joining link looks slightly wider than the rest…

Is it the correct ‘speed’ for the chain?

Assuming the cassette is new as you said, your chain is the correct length and chain line reasonable enough. Check the hanger alignment!

If it’s just noise the tolerance with Sunrace cassettes and KMC’s cheapest chain seems to be tighter and you get noise in certain gears, it wears away pretty fast though. I’m guessing both components are right at the top of there tolerances, so in combination bind a touch here and there.

If you are using an old standard (non-clutched) mech without Goat Link or Rad Cage mods, it’s the worst to set up and is flaky in operation IME. I tried it on one of my bikes, just because I could! and to compare it to a modded clutch mech, it was shite.

Just checked the chain and no stiff links but the joining link looks slightly wider than the rest and could possibly be getting caught between chainring and spider.

This.

Had exactly what you described and, after stripping and regreasing the freehub, I couldn’t solve it. Then, with the bike on the workstand, slowly turning the cranks revealed that – on the smallest couple of cogs – the chain could be seen lifting over teeth occasionally. The key fact was that this only happened as the quicklinks went past.
Further inspection revealed that the riveted end of the link pin was slightly longer than on any of the other quicklinks that I had in my toolbox.
Thinking back, the issue started shortly after changing the quicklink, because the old one broke.
Switched quicklinks, and the problem went away.

Could well be the quick link it definitely look wider, I will put vernier gauge on tomorrow.

Only does it in top & bottom gear? I’d be checkung the gear hanger alignment. Those are classic symptoms of it being out