Hi all.
I’m having chain slip issue with a recently cobbled together singlespeed.
It’s a secondhand Surley (i think) 18t sprocket on a new KNC BMX chain using a battered old dmr tensioner pulled tight ‘as’. The chain line is straight to the naked eye although the tensioner is at full lateral reach. You can see from the pic that the teeth sit proud of the chain and yet when under pressure i.e. climbing, the chain jumps. Any ideas?

cant tell from the pictures but i think you have the wrong chain. You need an 8 speed chain most likely or a 3/32 ss style chain. 1/8th looks too big for the rear cog…pictures arent clear enough though.

That could make sense. I’m also having issues with the LBS regarding high levels of BS. Re the pics is it the image quality or my camera skills? First time linking pics on here etc

The chain needs to be on more teeth I had this problem and used an old rear mech which engaged more teeth to solve the problem

your chain is way too long.

If you can’t take a full link out (inner and outer) then try getting a half link that is suitable for that chain width.

Push up tensioners are much better as they give you more chain wrap but if you can’t swap the spring (I assume it’s sprung?) then definitely try and get the chain as short as possible.

why would the chain width make a difference? I’ve happily interchanged 1/8 3/32 on the same drive chain.

My guess would be chainwrap around the rear sprocket, it could be better (although in itself doesn’t appear to be a problem. Could you shorten the chain or configure your tensioner to push up rather than down?

Freehub problem is the other potential.

just saw the spring.

This is what my merlin was like with a Surly style set to push up:

Looks like you have a normal 3/32″ chain. I was using a 3/32″ KMC Z610 with a half link like this: http://www.charliethebikemonger.com/kmc-half-link-279-p.asp

1/8th is BMX style (wider) chain.

Tried taking a link out today and I’m about 2mm short. Free hub, I’m fairly sure is sound. I guess chain rap is the obvious culprit. To use a push-up tensioner I’d need to shorten the chain I I guess a half link chain is in order?

The chain is a lot wider than usual mtb chains.

If you’re not sure if it’s the chain jumping the sprocket or the freehub slipping, then as long as you’ve got an even number of teeth on the sprocket, you can mark the sprocket next to a wide link.
Ride it until the slippage occurs.
If the mark is now by a narrow link, then you know the chain has jumped a tooth.

if it is wider then it is probably a 1/8th.

Click my link above – all you need is a single half link not a half link chain.

But I would use a proper 3/32″ chain if the chainring and sprocket are for 3/32″ chains and not wider for 1/8″ as the wider chain will have more play side to side which is not ideal.

Ive watched the chain ride up over the teeth whist pedalling so I’m confident it’s not the freehub

I ran my old SS the same way, 1/8th chain, 1/8th front ring, normal ss sprocket.

When i used it at first i got constant chainslip under load so i switched the tensioner to the pushing up spring (Surly singleator) and it never slipped again.

I no longer have the bike but i do have the Singleator in my spares bin if it’s of any use to you?

other think – are you using a proper single speed chainring or a normal geared one?

Thank you all. I do like that Bike Monger site, makes me want to buy a pipe and some cherry tobacco to smoke whilst listening to jazz. I’ll check the chain again when it’s light and will try a half link. It sounds more than likely it is lack off chain rap

Yep proper chainring.
Mr Tall I may well be in touch thanks

Hi all just wanted to update. Whopped a half-link chain on this week and it’s working a treat. Feels properly solid too. So Just wanted to say thanks for the advice