Cannondale si crank compatability

Can anyone enlighten me here. These cranks have driven me mad! Lol

Was working on the newer cannondale bikes. So the caad 12 and synapses. Says bb30 under the frame so though I'd change the crank over from a cannondale si crank to a fss bb30. Seems simple enough. However when installing the fsa one and bearing in mind I've installed the bearing covers and the wavy washer, once the bolt is tightened on the non drive side the crank arms are pressing hard against the bearings and the crank hardly spins. Tried taking off the wavy washer and covers etc and same problem. Tried different fsa cranks and different dust covers. Same issue.

I Checked the length of the spindle and yes the cannondale si cranks are a bit longer, but just from eyeballing it they have several spacers and with the spacers on the length of the spindle on the si crank looks identical to a normal fsa bb30 one.

Is there anyway to get the normal fsa bb30 cranks to work on these cannondales? Older synapse from say 2013 had a normal bb30 crankset. This seems to be an issue since the 2017 /18 range of bikes came out.

Finally, I just got tired and put the si crank on again. Wondering if these cranks are propriety with these frames and no other crank will work or am I just missing something simple here?

Thanks for any advice.

Yusuf

Possibly bb30a ?

@howard is the resident cannondale guru

Been a while since I looked at these but I suspect you are out of luck because your FSA crankset has an axle that's too short leading to the biding when you tighten it down.

The newer Cannondale frames use wider bottom bracket shells - 73 vs 68mm - meaning your FSA axle is 5mm too short.

Wondering if these cranks are propriety with these frames and no other crank will work or am I just missing something simple here?

There are other cranks that fit fine - any of the 24mm axle cranks can be adapted to fit as can BB386 and older SRAM 'BB30' 30mm axle cranks.

That explains it. Very much appreciated for your time.