Slipping one piece crank

It slips on rotation before it picks up the revolution. It's always difficult to explain
these things. Not sure how else to explain other than to say there's about 5mm of slipage
back and forwards before it starts to turn the wheel. You can tell by applying
minimal pressure when stationary so there's not enough movement to to spin the wheel.
Trust me, it's there.

Then it should be an easy job of identifying what is moving and what's not when you put some pressure on the crank.
Crank moves but chainring doesnt = interface between crank and chainring at fault
Crank and chainring move but chain doesnt = worn chainring or chain
Crank, chainring and chain move but rear sprocket doesnt = rear sprocket worn
Everything moves except the wheel = rearsprocket and/or lockring are loose.

For what it's worth id put good money on it being the 1st.

Basically it only slips when stationary ie track standing and the BB, crank,
chainring and chain slip in the BB housing a fraction back and forth. It i indicates
that somethings not tight in the BB area.
As I said I've tightened the cone as much as I can without it being too tigh, and
then the lockring as much as poss. It didn't slip before conversion tho.
I don't think it does fit in to any of the above tbh mate.
Will take it apart and check all your points tho, cheers mate.

1. low chain tension
   
2. slight movement between chainring - crank interface
   

3. tighten cog/lockring

4. one piece cranks have press fit cups, tried refitting them? or just strip out the bottom bracket, whack a load of grease in and tighten everything back up nicely?

Still reckon it's one of the first 3 though.

Any luck?

edit - or i think on some 1 piece cranks the chainring screws onto a thread on the inside of the crank arm, which could be loose. is it like that on yours?

Worn sprocket? That would do it too

Could do with a bit more chain tension, I'm in need of a half link, but it's not that bad.

The movement is only in the BB, no where else.
Have tightened everything after removing and re-greasing everything.

I am right in saying that I can't tighten the BB too much right?

Wait, is this a BMX style one-piece?

So the chainring is held in position by a hole on the side, and the hole in the middle?

If so... is the chainring still round? Is it sitting snugly on the crank?

I don't believe it's your BB, I think it's something else. Sprocket or crank if you think your tension is good.

This thread needs pictures, or the bike needs to make its way to one of the drinks/polo/gathering of people who can help.

Ha, you're right, as I said it's difficult to explain.
And yes, it's a BMX style one piece with a new chainring which is sitting as tightly as it can.
I'll post pics after lunch, and I'm at Souths on Weds. The new girl on the block.

Cheers guys.

Half a link worth of slack is enough to get this sensation - can't you get any more tension or you got vertical dropouts?

Shit, sorry, not awake yet. Half link issues is with other bike. The tension on this one is about as tight as it can get.

Has Souths moved to Wednesday now or am I missing something?

souths polo? I'll be there on wednesday and can take a look

Sorry Damnit, I meant polo if you thought I was referring to drinks?

Cheers DT. I'm the one who stole your Wheel disks. ;)

Nice one, thanks.