Syncros revolution cracked powerplate - advice?

[zepreeme]

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.

 

[fguki]

If you consider the recent prices for Revolutions, I would consider having one whole new baseplate reproduced in a machine shop.

 

[Fatboy1974]

I would machine a new one. I know some reliable taiwanese partner that can do a good price. I did some seat clamps batch at good prices. Maybe you get it at 60-80€.

 

[zepreeme]

I would machine a new one. I know some reliable taiwanese partner that can do a good price. I did some seat clamps batch at good prices. Maybe you get it at 60-80€.

Thanks for the reply. I will look into making a new baseplate. Could you perhaps share some info to them in PM to me?
Thanks

 

[zepreeme]

If I somehow was able to press out the baseplate without damaging the crankarm I can take the measurements and make a copy. According to Syncros catalog the square taper/baseplate was cold forged. Quite a project

 

[Lucidone]

So that's quite a construction!
Does that suggest that the square taper is originally a separate 'plug' that is pressed into the baseplate (presumably) after the crank arm has been pressed on?

 

[zepreeme]

The whole baseplate is “complete” with the square taper hole as well.
Here is another picture from a MTBR thread showing the other side.

Perhaps cold forging is not necessary for a replacement.

 

[Betsy]

I'd assume the manufacturing process would be as follows..
Square taper is forged into a blank, the blank then fits onto a square taper peg in a threading machine (like a dummy BB spindle), the thread is cut.. the thread is then used to bolt the blank to another peg/dummy BB spindle in a lathe and finally the blank is spun into a base plate from the forged taper, centralising the base plate to the forging.

Cheap to make lots.. expensive to make 1

 

[Lucidone]

@zepreeme Ah, makes a lot more sense now thanks!

 

[synchronicity]

Would adding 5 new holes (marked with purple) make the plate much weaker?

No. There is plenty of material remaining there to work with.

However if you are that cluey with CAD, then just get a new plate machined from scratch?