caution* lunati cranks bad
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From: Upstate NY
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From: pa
We built 2 mild motors (under 500 rwhp) and both cranks broke in two weeks. We called them and spoke with allison she said they changed there heat treat process and was sorry so she is sending us two "old stock" cranks made before june/03. The problem is they are getting them to hot making them brittle.
## Dont take it wrong. I do not wish to bash any company. I like lunati and they are doing what they can to fix this problem. The perpose of this is because like me i know alot of you are doing your winter stroker buildup's. I dont think it would be a good thing for anyone to spend all that time and money to have the motor last 2 weeks. Then have to tear it out and back down again when i can give you the heads up till they fix the problem. I wish lunati well. I love to know that they see a fault and are fixing it.
## Dont take it wrong. I do not wish to bash any company. I like lunati and they are doing what they can to fix this problem. The perpose of this is because like me i know alot of you are doing your winter stroker buildup's. I dont think it would be a good thing for anyone to spend all that time and money to have the motor last 2 weeks. Then have to tear it out and back down again when i can give you the heads up till they fix the problem. I wish lunati well. I love to know that they see a fault and are fixing it.
Last edited by amean94ta; Dec 2, 2003 at 05:13 PM.
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by amean94ta
We called them and spoke with allison she said they changed there heat treat process and was sorry so she is sending us two "old stock" cranks made before june/03. The problem is they are getting them to hot making them brittle.
That sounds like the "tempering" part of the heat treating process was done at the wrong temperature or missed. After either through hardening or case hardening (nitriding, for example), steel needs to be tempered or reheated at a fairly low temperature (350*F to maybe 750*F) to "draw" out some of the hardness and brittleness and stresses. If the temp is too low, the metal will be very hard and wear resisatant, but brittle; breaking could result. If the tempering was missed completely, there are a lot of unrelieved stresses as well as high hardness, and it could fail easily.
That's not the only possibility, of course.
Most manufacturers do not do their heat treating in-house. They use heat treating companies who can afford the large expensive equipment necessary. Typically there would be certification and test results accompanying the heat treated parts. The customer could (should?) also check the parts for hardness when they get them back. Unfortunately, you can't always find improperly heat treated parts with a simple surface hardness test.
I suspect there might be one batch of cranks which were wrong, and that this is not an on-going problem. There are other possibilities, of course.
My $.02
Dont take it wrong. I do not wish to bash any company. I like lunati and they are doing what they can to fix this problem. The perpose of this is because like me i know alot of you are doing your winter stroker buildup's. I dont think it would be a good thing for anyone to spend all that time and money to have the motor last 2 weeks. Then have to tear it out and back down again when i can give you the heads up till they fix the problem. I wish lunati well. I love to know that they see a fault and are fixing it.
We called them and spoke with allison she said they changed there heat treat process and was sorry so she is sending us two "old stock" cranks made before june/03. The problem is they are getting them to hot making them brittle.
That sounds like the "tempering" part of the heat treating process was done at the wrong temperature or missed. After either through hardening or case hardening (nitriding, for example), steel needs to be tempered or reheated at a fairly low temperature (350*F to maybe 750*F) to "draw" out some of the hardness and brittleness and stresses. If the temp is too low, the metal will be very hard and wear resisatant, but brittle; breaking could result. If the tempering was missed completely, there are a lot of unrelieved stresses as well as high hardness, and it could fail easily.
That's not the only possibility, of course.
Most manufacturers do not do their heat treating in-house. They use heat treating companies who can afford the large expensive equipment necessary. Typically there would be certification and test results accompanying the heat treated parts. The customer could (should?) also check the parts for hardness when they get them back. Unfortunately, you can't always find improperly heat treated parts with a simple surface hardness test.
I suspect there might be one batch of cranks which were wrong, and that this is not an on-going problem. There are other possibilities, of course.
My $.02
Dont take it wrong. I do not wish to bash any company. I like lunati and they are doing what they can to fix this problem. The perpose of this is because like me i know alot of you are doing your winter stroker buildup's. I dont think it would be a good thing for anyone to spend all that time and money to have the motor last 2 weeks. Then have to tear it out and back down again when i can give you the heads up till they fix the problem. I wish lunati well. I love to know that they see a fault and are fixing it.
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