Campagnolo chainring spacer 4 arm 42t

[Ryun]

looking to be pointed in the right direction:

Finally sourced a 42t inner ring for a 4 arm Campy cranks 11sp.

the 4 arm normally uses one bcd for the outer ring and another for the inner ring. In the case of the 42t, it attaches to the same location as the big ring. The package included new chainring bolts but looks like I would need spacers between the two rings. Any guess on what size spacer should go between the rings? Or am I completely missing something?

Thanks
Ryun

[Mark McM]

There's no need to guess - the chainrings are parallel to each, so the spacing between chainrings will be equal at all attachment points. Just measure the width of the arms at the other 4 bolt holes.

[Ryun]

It is tough to get a precise measurement on the depth needed.
and knowing the tolerances are tight on 11sp makes me a little nervous
Here are a couple pics:

I could get a rough depth on the drop to the molding for the inner bolt.



Right now my best guess would be that the hidden spacer on a five arm might be the correct thickness so I am going to pull one off and see if I can source four of that thickness

[Mark McM]

Oops, sorry, in my first response I though you were referring to hidden 5th arm cranks.

Yeah, the same width as the hidden 5th bolt spacer on a 5 bolt chainring would be my guess as well. But here's a way to directly measure what it should be: Mount only the outer chainrng; hold the crank against a flat surface so that the mounting post flats for the inner BCD are against the flat surface; measure the distance from the flat surface to the inner face of the outer chainring. (Said flat surface used as a measuring plane could be something as simple as a straight edge spanning acrosss holes 180 degrees apart). The space between the reference surface and the outer chainring should be same as the spacers required.

I'm wondering: Where did you get the 42 tooth chainring? I can't see it in the Campagnolo spare parts catalog. And it seems strange that it would include the extra long mounting bolts, but not the spacers.