Campag Pista chainset question

[scampi]

Hi,

I unearthed this old Campag Pista track chainset from my box of old bits.  The chainring bolts look odd - they don't appear threaded and I wondered if that was how they were meant to be, or whether it was old bolts that had sheared off.  They seem pretty firmly fixed, and before I started trying to knock them out I'd be very grateful if anyone could enlighten me!  Pics below.

[LittleWheelsandBig]

Those chainring nuts have a fine external spline and, once fitted the first time, are semi-permanent. You can knock them out but it is better to leave them there.

It does look like somebody didn’t grease the chainring bolt threads and broke off the bolt heads. I would try carefully drilling from the back, which may release the bolt remnants. Otherwise just push out the nuts (don’t try turning them).

[giropaul]

I’ve had chance to have a look at my Pista chainsets.
It’s confirmed my suspicion that the slot ( for a special tool to fit to stop rotation if the knurling doesn’t) seems to go across the base.
It does look, in your photos, that someone has fitted a bolt, but then broken it off. I could be wrong, getting a proper look at mine might involve an expedition into the store.
Why someone would do that, to all 5 bolts I have no idea.
Your reported lack of internal threading might support the idea though.
Are they the 151 BCD model?

[hubner]

The part with the slots is the "nut" and has an internal thread, and push fits into the crank from the back and should not be turned. The crank holes are not threaded. The "bolt" has an external thread and screws into the nut and is turned with an allen key. This is standard fitting for most cranks.

It looks like all the bolts have had their heads cut or ground off, I doubt if they could break off from overtightening, the threads would strip first I would have thought.

The remains of the bolts should spin out if they haven't seized.

[scampi]

Thank you for your replies - much appreciated.

Are they the 151 BCD model?

144 BCD

[Paul]

… It looks like all the bolts have had their heads cut or ground off, I doubt if they could break off from overtightening, the threads would strip first I would have thought.

How interesting. Maybe the bolts were all rounded off and couldn’t be removed with the correct tool (Allen key, presumably)?