One of my mates just stripped down his 2332cc motor to see what suddenly caused a nasty metallic bottom end knock after 15 thousand miles of road (never been on a strip) use and found this.
Its a CB Performance 84mm forged chromoly crank.
A closeup of the break.
CB performance have basically said words to the effect of "there is not any kind of warranty".
So thats one wrecked crank and a damaged case.
Is this just a one off thing or has it happened to anyone before?
I used to work at a vw parts shop and they had several CB 4140 and 4340 cranks. I sold one to a friend, and after 10K miles it broke the exact same way as yours. I thought it was the way my friend drove but after seeing your crank I will have to apoligize to him.
My mates gonna get it checked out by someone that works for BAE making plane parts and has access to all the tools to have a proper look.
If it is a manufacturing fault is there likely to be any way to get anything back off CB?
I know they are all made in china or somewhere but there still should be quality controls in place.
It is an excellent example of the famous two part guarantee, "if it breaks in half, you get both pieces" - it looks like there was a flaw that worked itself back & forth until it snapped. Would a magnaflux have caught this?
Some of the guys at the local Strip will only run Cast cranks in their V8's because they say Cast Cranks will flex more and not break but Forged one's are more brittle and tend to get stress fractures and break more. I always thought that Forged cranks were suppose to be better but I guess Cast cranks are more even in the properties of the metal so they don't get stress fractures like a Forged unit will. I wonder if they stress relieve the cranks after forging or not?
I bought a 4340 CB 78mm crank off EBay, only to see how they compared to an original VW crank that had the DPR treatment. I sold the CB crank cause i didn't like it, now i know why. Thats not good that that happened to your mate, engine failures suck big time. He has my sympathy.
Yep they're a big kick in the you know whats.
Especially since the case and crank cost him the equivelent of about 1800USD due to the stupid cost of parts here in the UK.
TNFrank wrote:Some of the guys at the local Strip will only run Cast cranks in their V8's because they say Cast Cranks will flex more and not break but Forged one's are more brittle and tend to get stress fractures and break more. I always thought that Forged cranks were suppose to be better but I guess Cast cranks are more even in the properties of the metal so they don't get stress fractures like a Forged unit will.
I think you got the cranks mixed up. Cast iron is very brittle and will break if you try to bend it only a tiny amount. The only advantage a cast crank has over a forged crank is price.
I'm not talking about Cast Iron, I'm talking about Cast Steel like this crank is made of: http://cgi.ebay.com/ebaymotors/NEW-SB-C ... dZViewItem
Cast Steel cranks don't have the same problems with the metal being stressed like a Forged crank does.
made in china? inproper grain flow, improper grinding, balacing, etc many things not done to those cranks, but the price is "good"? compaired to "real" cranks, like $400 for a CB, and 2k for a Berg .
Chromoly grades varey in different countries. when a company says 4130,4140,etc There really should lie a questionmark behind it. It really doesnt stand for much.Its kind've deceiving.
US mil. spec 4140 and chinas version are 2 different qualities.
I dont know the difference in torsional,tensile or shear strengths.
I assumed the grading on chromoly (4130, 4140 etc) was an industry standard number so would not vary from manufacturer to manufacturer (or from country to country) but you know what they say about assume? It makes an ASS out of U and ME.
Some good news is that my mate is now making a turbo'd and fuel injected 2165cc instead of his 2332cc NA motor. Should make him happy again.
