I was (a few years ago?) truckin' along with the motor build, most of which involves rounding up the necessary parts and cleaning. I don't care for cleaning parts but I do enjoy looking for parts... as I get back into the project I'm hoping to be able to share something other than me pulling my hair out trying to make carbon parts!
These showed up from the other side of the Atlantic (if it's even still called that
) a few days ago.
Quote:
Originally Posted by Jonny042
Just closing the loop one these - I never did hear back from Rosepassion who could not get an answer from their supplier as to how their alu sprockets are made, or from what. Not really a very comforting feeling. Certainly they don't even look to be anodized.
I ended purchasing a full set of 6 sprockets and 2 drive hubs from a different source in the EU (they are made in a different part of the EU) and was able to get commitment from the manufacturer that they are 7075, with hard anodizing.
They showed up yesterday, and are darn pretty. And pretty light! From my measurements they will save a little over a kg (2.2 pounds).
Not only that, they are pretty hard. Brinell hardness of the anodized surface averaged 144, a small portion with the anodizing removed showed 138. This corelates to the hardness you should see with heat treated 7075.
The original steel sprockets (one from a 3.0, another from 2.7) measured today with the same hardness tester a value of 81 Brinell. I can't even find an example of a steel that would have such a low hardness. Even mild steel should be 120 or so.
A newer set of "OEM" sprockets that I previously tested had a hardness of 119 (going from memory on that one).
Cheers! |
I've only been able to gather opinion on the longevity of these. The lone factual data point is from Grady Clay who worked on a motor that had them for 40,000mi but it's unknown the material construction of those. Possibly they were factory 935 parts that by the looks of it weren't hard anodized, although they could have been heat treated post machining but the amount of scratching on these makes me think they are a bit soft. Some 935 for sale in the classifieds in 2006:
As you can see I've done my homework, but homework was never my strong point... still, I'm going to follow the science and run these with confidence.
Many thanks to Brookieslayer for the help with the hardness testing!