What feels like the cranks skipping a beat

I've recently put together my first build and I've noticed something odd. When I resist the pedals hard, or push down hard to accelerate, the cranks seem to skip. This does not occur everytime (has only happened about 4 times) but only happens when doing this. I've only just put the cranks on, so they're super tight (maybe too tight?). I thought it may be the cranks skipping on the BB spindle but surely it would only happen to one crank, as both would have to had moved the same turn together which would seem unlikely. The BB cups are nice and tight, there is no play in the spindle, pedals are on securely, cog and lockring fully tightened, everything's nicely greased. Anyone know what the 'skipping' could be?

Thanks!

Explain to us what you mean with 'the crank is skipping'. I don't get it.

It's weird, it feels like a momentary loss of power and then returns to normal in a fraction of a second. People can notice it when watching too. But can't actually tell what's moving / if anything is moving / what's wrong.

Power up a hill/use a chainwhip to tighten the sprocket and then do the lockring up properly.

You are using a lockring, right?...

slack chain then cranks taking up the slack.

That's what I thought it could be at first - the lockring unwinding slightly - but I've tighted up the lockring with correct tool while the lockring has been tight on from forward pedalling use.

Chain ain't too slack, I suppose it could be that though. But wouldn't really explain the very few instances of it - as I guess if that was the problem it would happen almost everytime..?

please see my posts in this recent threads. it's a slipping spocket / lock ring ( i think).

http://www.londonfgss.com/thread28845.html

a slack chain would be constant.
check that the spocket has been put on probably - and make sure you clean the thread of any shavings (that should be good indication if it is slipping).

that's 3 of the same question on one page. but each one has blamed it on a different thing, cranks, chain and i cannot remember the last

that's 3 of the same question on one page. but each one has blamed it on a different thing, cranks, chain and i cannot remember the last

Jesus?

Jesus?

no i don't think jesus was involved in this. well potentially he may have been but i don't think so.

Cog
Lockring
BB
Chainline

If it was chainline, would the chain not ship rather than just momentarily feel like a slip? Rhetorical question.

Checked the chainline, almost perfecto - cog is maybe a mm or two further out than the chainring. There's a slight bit of noise, but nothing out of the ordinary.. Hmm. I think the problem may have stopped now though, ain't experienced it in a while - probably was lockring not properly tightened.

tighten your cog properly, do search for slipping cog.

i would've thought slipping lockring/sprocket. even if you tighten it up, it might be misthreaded, like if you look close up half of lockring is flush to sprocket and on the others side there is tiny gap, one thread's worth

i would've thought slipping lockring/sprocket. even if you tighten it up, it might be misthreaded, like if you look close up half of lockring is flush to sprocket and on the others side there is tiny gap, one thread's worth

This same question comes up about once every two weeks and it's always a loose cog. There was another one only a day or two ago (yes I am at work that's why I'm on here all the time at the moemnt).

What cranks are you running?

get rid of the biopace chain ring and get a round one

Some Sugino 170 double chainring ones which were on the frame when saved and the chainring is a Sugino BMX. All sorted right now... as yet...

The problem came back again today after doing a load of skids. So, I've taken off the cog and I'm going to get it nice and tight again tomorrow morning, and get it nice and secure.

Also, I found a great tool-less way to remove a cog which is hard to remove (just do the opposite of what it describes, as this is for installing a cog) - http://204.73.203.34/fisso/eng/schpignone.htm

That may already be well known? But it worked a treeeeat for me :D

it is well known, but a chainwhip is still a worthy tool to use.

what gearing are you running?

If the cog tightens from pedalling, then the lockring will loosen. fit cog, ride up a hill, then retighten lockring. If it's still happening you've probably fucked the threads on your hub.

Some people report slippage on 3 piece BMX cranks, but I cannot tell you why.

I have also noticed slippage with an old stronglight crank set, which had a bolt on spider. Check the chainring bolts, if one of them is loose or missing, then this will cause slippage and also irreparable damage to either the chairing, crank spider, or both.

The problem came back again today after doing a load of skids. So, I've taken off the cog and I'm going to get it nice and tight again tomorrow morning, and get it nice and secure.

Now you have removed the sprocket, check the hub's threading. Does it all look intact?

get rid of the biopace chain ring and get a round one

You will be surprised, but Biopace works fine on a fixie or singlespeed.