Originally posted by tonimccloud
Hi,
this weekend was a bit frustrating for many racers here in Spain. Some friends bought, one or two months ago, the sts dragon D3 from rcmushroom. Everything was ok, the engine works very well, more or less the same performance as the most expensive engines in the market.
Well, with five liters more or less, 4 engines went broken, and we don't know why. And the same for the 4 engines: the crankshaft (you can see the pictures here http://www.cochesrc.com/foros/viewto...r=asc&start=40 ). Do you know why? Is there any trouble with STS crankshafts? I was planning to buy one, but now...
Can you get larger pick of broken side of metal, if I can see metall structure may be able to say something. I general can be two things-wrong steel or wrong temp hardening parameters ( most likely overhardened). It is happened when shaft hardened all the way through with the same Rockwell. Usualy we hardened shaft to 45-48 internal and "skin" to 65-68.
I don't think it is mistake of design, it is more look like mistake of technology.