chain 'slipping' on full power/top gear

[powerlord]

I'm no bike expert, and I've been through all the 'googled fix chain slipping' links.. so hoping you guys can help.

build brand new bike - 13 incline alpha 27 speed.

converted to BBS02 with a 48T chainring.

Set up the gears to change smoothly, etc and all rides well, but in top gear (on the 11T) at full power (either full motor power of full 'me' power) the chain is slipping a cog every once in a while - not every rotation - but every 3 or 4 seconds. If I don't really go for it in the 11T, and have the motor off or just on a bit then it's fine too - it's only on full load that it's slipping a cog.

brand new chain, etc but none the less I have checked every single link for stiff links and all fine.

Obviously cassette is brand new.

So no chance of anything being worn out.

What am I missing ?

It only slips on the 11T and thats of course where the most load is being put through it at the highest speed but still - it shouldn't slip.

I notice that if I take the chain off, there is some movement on the rear cassette - you can rotate it back and forward a little before wheel moves or freewheel kicks in... is this normal ?

So got me a bit flummoxed at the moment ?

stu

 

[keithmac]

It's quite a small sprocket, the chain doesn't have many teeth to mesh into therefore it is more likely to slip under power.

Is the chain under decent tension in said gear?.

 

[powerlord]

I've adjusted the rear derailed pulley to be as close in as possible.

With the 48T I needed the full chain length of a new chain to get into largest rear cog, so replaced original chain with new one for that - original one wouldn't go into largest rear cog as had stretched rear derailer out as far as it could go by then.

Now, in the largest rear the derailer is still out about vertical but plenty of movement left.

So when in the 11T it's not possible to adjust the rear derailer pully right in to the cassette as it was with the standard chain, but it's as close in as it will adjust to.

Not sure if that means more or less tension ? but certainly feels like plenty tension on the 11T.

stu

 

[powerlord]

hmm.. you got me thinking - pictures worth a 1000s words.. attached on biggest and smallest.

I think maybe chain is too long as you say ?

 

[E-geezer]

An easy way to set the chain length is to put the chain in the largest cogs and add 2 links. If it's a FS frame, you might need more to account for chain growth.

Check the B screw adjustment as well.

http://www.singletracks.com/blog/mtb-repair/how-to-adjust-your-rear-mountain-bike-derailleur/

It shouldn't skip if everything is new and unworn.

 

[spinningmagnets]

The more the derailleur is stretched out, the tighter the coiled springs are, so shortening the chain can make it more stretched out when it is in top gear. You might also add a chain tensioner on the bottom run of chain, pulling up (as an option?) I don't know if that will help, but I think its worth investigating.

The stronger the derailleur springs are, the harder it would be to shift, so manufacturers try to strike a balance, but...if its possible to swap-in a stronger spring, that would help.

The 48T/11T combination is the same as a 60T/14T. I don't know if you could adapt a 60T to the BBS02, but if you could the driven gear would go from having 5 teeth engaged with the chain, to having 7 teeth.

 

[Wheazel]

One of the most common causes to chainskip on small diameter rings, is that a link in the chain isnt moving smooth, and therefor doesnt wrap around the small diameter sprocket as intended. Check your chain.

 

[KINNINVIEKID]

I had the same problem but solved it by lubing the chain with Muc Off C3 ceramic wet chain lube.
Now I can use full power on the 11T sprocket even running at 1400W.
https://muc-off.com/products/c3-wet-ceramic-lube

 

[dogman dan]

Agree with above, take a hard look at the link where the chain was broken to install it. One stiff link can do it.

Tedious, you have no idea which link, test every one for smooth bending.

 

[powerlord]

So - all working now ! no more slipping.

thanks for folks help.

I took 2 inches out the chain length, and then started from scratch setting up gears again.

I also lubed the chain with Muc Off as recommended.

I think a combination of chain being too long, it maybe not being set completely correct on the bottom cog and scraping on the second gear enough that under load it caught it a bit and slipped a cog was probably the cause.

It's now super smooth.

 

[Hillhater]

That 2" out of the chain would make a big difference to the tension on the chain from the derailier.
That would be the key i suspect !

 

[dogman dan]

Solved,, great..

One other thing I just thought of could have been the culprit. On most bikes, the chain line from the big gear up front to the tiny gear in back is very straight. If for some reason it was not,, that could cause problems.

just added that for reference purposes.