Play in cranks/chainring help?

When I'm riding or just sat on the bike there's some slight play somewhere and I'm confused as to how to stop it. When I pedal forwards there's a tiny moment just before the the chain engages and pulls the bike forward where nothing happens, the cranks just move with no resistance. It's only brief, but now I've noticed it happening it's hard to ignore.

I know the explanation isn't brilliant, but that's the only way I can describe what's happening.

Anyone any ideas?

Just slack in the chain, no?

Not necessarily in a bad way, if it isn't excessive: search "chain tension".

I got the tension as tight as I possibly could without being too tight.

Free wheel pawls don't catch ?

Possible too: I assumed MrFixed was riding fixed.

Chris King hub needs servicing?

I'll double check the tension.

Could possibly be the hub. The bikes been in storage for over a year till I'd bought it, so it's been neglected somewhat.

I also vote for play in bottom bracket bearing. Try wiggling the crank orthogonal to normal direction of travel. If it moves, that's bad.

There's no lateral play in the bottom bracket, just forwards and back. There's a slight delay before all the drive chain engages. It's more noticeable when back pedaling, as you feel the gap where there's no resistance and then it grabs again.

What type of crank/chain ring?
My ESB's bmx chainring spider had a small bit of play so I reinstalled it with metal glue and has been fine since.

Fasten the chain to a stay using a tie wrap (zip tie?) or some such. Then you can isolate hub or crank/bb problems. My money is still on hub/freewheel trouble if this is SS and not fixed. Play in BB would have to be huge to make it feel 'slow' like this. Spinning for half a revolution before catching on happens to old/cheap/abused freewheel hubs and would produce the effect you mention.

It's not happening to that degree, not half a revolution more like the tiniest bit, but it's irritating

Are you riding fixed or not?

Do a hill
Tighten lockring

Substitute hill for chainwhip if you have one.

needs moar pawls....

I got the tension as tight as I possibly could without being too tight.

This suggests you do not have a geared drivetrain.

It would really help if you'd tell us whether you are fixed or freewheel.

"...as tight as I possibly could without being too tight..." sounds like a bit of an oxymoron.

If you are not sufficiently experienced to set a chain at correct tension and to identify the slack that will be felt in a correctly tensioned chain while trackstanding* etc then I suggest you befriend someone who is and ask them to teach you.

*This kind of presumes you are riding fixed.

If you are riding freewheel then excess tension in the chain may cause freewheel pawls to not engage correctly, befriend mechanically minded person as above.

I've had a double check because I've not ridden for a few days. There is play everywhere, laterally, front and back. I don't know whether it's a case of just tightening up or replacement BB. If it is a case of replacing the BB does any one know what size etc I'd need?

It's a Fuji Classic Track 2010, for the most part it's been kept relatively close to stock componentry.

If the axle is moving from side to side wrt bb, then you need a new bb. Take out the old one and get another one the same length.
If the crank is moving wrt the axle, then you need new crank. Maybe some self flagellation might be useful, as might changing the bb, but probably not.

If you're talking about play in the wheel, then if it has sealed cartrige bearings, you need to switch the bearings. If it has cup an cones, you can prbly sick in grees and tightenit up.