Syncros revolution cracked powerplate - advice?

[zeepreeme]

Hello.

Looking for some advice on my Syncros revolution cranks. I've found some cracks at two of the mounting holes on the "powerplate". Unfortunately in it's earlier life someone drilled and enlarged these holes to allow for regular chainringbolts to be mounted (8 to 10mm). This made the the material at the outer edge quite thin. I won't be riding hard with these, but still use them so I would like to ask what you think?

Instead of relying on the remaining three holes, I thought of machining 5 new M8 holes in the powerplate to allow for mounting a complete circular plate that could replace the spacers, with standard chainring screws (only screw part).
Would adding 5 new holes (marked with purple) make the plate much weaker? it would somewhat be compensated with the new "spacer ring" (gold) in 7075 alu. The 5 new holes will be covered by the standard spider. so won't really be visible from the drive side.




Mounting the small chainring will use standard chainring screw and barrel.




Thanks for looking and looking forward to hear your thoughts.

 

[BikingDevil]

If u have the possibility to machine these parts, why don't u just machine the powerplate and replace it? I would just weld the cracks maybe at first and try out how it works...

 

[zeepreeme]

That would have been good but I saw a disassembled one once and believe it has some splined interface and press fitted into the crankarm, as well as some kind of epoxy. Making the spacer plate I can do myself, but not a complete powerplate with the square hole.

Thought about welding but can’t heattreat with the crankarm I think?

 

[Bo-Bo]

I can't assess it professionally - but is there any load at all in the intermediate areas of the powerplate?

Here is an FEM representation of a bicycle crank that may help you with your assessment.

stolen from the interwebs:

https://www.gknpm.com/globalassets/...bel-sowie-abgleich-mit-dem-bauteilversuch.pdf

 

[931M]

That would have been good but I saw a disassembled one once and believe it has some splined interface and press fitted into the crankarm, as well as some kind of epoxy. Making the spacer plate I can do myself, but not a complete powerplate with the square hole.

Thought about welding but can’t heattreat with the crankarm I think?

Das wäre gut gewesen, aber ich habe einmal ein zerlegtes Exemplar gesehen und glaube, dass es eine verzahnte Schnittstelle hat und in den Kurbelarm gepresst wird, sowie irgendeine Art von Epoxid. Die Herstellung der Abstandsplatte kann ich selbst tun, aber nicht eine komplette Powerplate mit dem quadratischen Loch.

Dachte an Schweißen, aber kann nicht Wärmebehandlung mit dem Kurbelarm ich denke?

 

[Thomas Sommer]

I wouln't worry much about the cracks at the outer edge and I think your construction
would fix them. But for my eyes there's a much more alarming crack in the inner area,
aiming towards the square hole!

 

[zeepreeme]

I wouln't worry much about the cracks at the outer edge and I think your construction
would fix them. But for my eyes there's a much more alarming crack in the inner area,
aiming towards the square hole!

Thanks for pointing that out. Hmm.
Perhaps the best route would be to actually try and replace the baseplate. Found some pics online of a disassembled crankarm and baseplate. If i can get the baseplate off I could design a replacement.
I’d have to have someone machine this for me, though the square taper is cold forged on the original.