steel crank? I talked to a grinding/balancing guy who said he won't guarantee a steel crank that leaves his shop against breaking unless he nitrides it.
Hollis Franks
Black 63 1/2 XL R Code
Gray 65 289 Falcon Ranchero
This message has been edited by hfranks on Dec 19, 2008 9:36 AM
It will harden the bearing jurnals and the surface of the rest of the crank. This is a benifit to the the jurnals for wear resistance. Your still going to have the same hardness core in the crank.
Nitriding does not harden thru and thru so it will not keep it from breaking.
Hollis, Stock mild steel cranks such as 1018 or 1040 are too soft for most HP application. Nitriding case hardens the crank to a specificed thickness that is determined by the length of time the crank is immersed in the nitric salts. Usually about 8 hours for a case thickness of about .030".040" depending on shaft diameter. A single quench process the crank is 'cooked' at 1675 F for the specificed time and cooled, reheated to 1425 F, water quenched then tempered at 350 F. On typical 1018 steel this should produce a case hardness of 62 on the Rockwell 'C' scale.
60 Starliner 460, 61 Starliner 427, 66 Galaxie 428, 67 Fairlane 427, 66 Fairlane 390, 69 F-250 390, 72 Lincoln 460 and 3 Ford powered Hotboats
Nitriding the crank makes it more scuff resistant. In some types of racing the bearings can make hard contact with the crank journals and wear the journals out after just a couple of races. Regrinds can be spendy if needed more than every couple seasons. Nitriding allows hard bearing contacts without causing wear. This allows the cank to outlast dozens of sets of bearings without maintenance.
Nitriding does not make bearings last longer, nor does it make the cranks stiffer or stronger. It is not bad idea, just might not be needed, depending on how quickly you wear out bearings.
argumentation. Any extra hardness on a surface actually does make the part less prone to breakage. To give a very extreme example, a steel tube is a construct consisting of a steel surface and an interior of air. In that case, ALL the strength is in the 'surface'. Now, if you make the tube very thin---the nitrided surface, and fill it with steel (or cast nodular iron) you make it immeasurably stronger. But, to go back to our crankshaft, the hard surface does, to some extent, aid the strength of the whole thing. JMO
KS
Moldex doesn't agree with CSC on the benefits of nitriding iron cranks. I've discussed nitriding of iron cranks with Bob on several occasions. He approves of it for all the reasons offered above, and in this thread. KS
This message has been edited by cammerfe on Dec 19, 2008 12:39 PM
But in fact, since the lenght and mass of the crank is what it is, A Nitrited, (case hardening) of .030 to .040 X 2,not even 1/16 inch deep, for the diameter, will have no affect on strenghting the crank.
Think about it. If what you say is true and reliable, I think we would have cranks made from hardened tubing and filled with T6 aluminum.
'no'. Read what I wrote. I did not claim that it made a major difference. But it does exist. And fabricated crankshafts have been built. It's simply that with our existing technology we can easily make cranks in better ways.
KS
Surface hardening from either Shot Treating, Thermal treatments or Chemical Treatment induces a hardness in the surface that resists crack formation. While resistance to wear is a nice feature the fact is ALL all cracks/fractures start very small and grow to LOL epic proportions like when an FE Crank Breaks in two!.
Now the bad news any surface treatment is without any doubt far more science then art (if done properly - not by Backyard Joes Metal Conditioning.
Ive been a long term subscriber to Shot Peener Magazine due to my selling filters to the industry and one thing I can say is I respect the industry for the absolutely amazing things done to metal surfaces that enable exponentially longer life of components from drive and transmission gears, connecting rods to helicopter blades. The science and it is in no way an art is amazing and complex. Chinese Joe doing metal conditioning of a Connecting Rod LOL THAT is where you have brittle failures. These guys know their shit.
In my limited research long ago I don't recall studying the crack resisting properties of treated cranks. The stories typically focused on crank maintenance related to scuffing. Reduced fatigue would be a result of crack resistance. I'll have to look into this.
Iron cranks can and should be treated. The trade name for treating iron escapes me now but I trhink it is similar to Nitriding. It does not have quite the same effect that treating steel cranks but it does help. I have a 514 BBF, cast Ford crank that was treated. Engine ate the no. 4 main bearing due in most part to my neglegence [spun the engine to 7500 rpm before the oil was fully warmed] Bearing did not spin but came close, bearing was wiped out and did some damage to the block but the crank was fine, just needing a minor polishing. If the crank was not treated I believe the journal would have been trashed too.
60 Starliner 460, 61 Starliner 427, 66 Galaxie 428, 67 Fairlane 427, 66 Fairlane 390, 69 F-250 390, 72 Lincoln 460 and 3 Ford powered Hotboats
that article didn't adress iron/cast cranks at all. But futher above, the Crankshaft Co. article did and they stated......
"What about cast iron crankshafts? Do they need to be hardened? The answer is no. During the machining process, cast iron crankshafts become work hardened. If a more durable crankshaft is desirable for your application, it would be a good idea to look into purchasing an aftermarket steel crankshaft."
Austempering nodular iron cranks makes for a durable racing crank, but that is a full-crank treatment, not a journal treatment. Also, the thermal expansion coefficient of an austempered crank is notably different than regular nodular cranks or steel cranks, so special consideration must be given to bearing clearances.
I am also aware that malleable cast iron crank journals must always be heat treated to make the journals durable enough for normal driving or racing. I am unaware of any journal heat treatment process for nodular iron cranks. If you can find the name of the process, please post it.
There is a Very big differance between nitriding a rod jurnal and tempering the total crank.
All I was saying was that Nitriding will Not creat a hardened crank. It will enhance the durability of the bearing jurnels but not the over all strenght of the crank.
Anyway the original question delt with a forged crank and most forged cranks are made from 4340 steel. So with a normal heat treat and Austemper it will be far stronger then a standerd cast crank with the jurnels nitrated.
I can believe that most low cost racing cranks are forged from SAE4340 alloy steel. I doubt any are austempered, but I can see most of them may have nitrided journals.
some mis-statements. Nitriding, in fact, DOES treat the entire surface of the crank, and not just the journals. The ENTIRE surface of the crank is hardened. And I don't think anyone has made any statement suggesting that a cast crank can be made to be 'stronger' than a forging. Stronger is a generality. Each sort of construction has its place. But that's a whole different discussion.
KS
Malleable cast iron crank journals must be heat treated.
December 19 2008, 5:10 PM
Malleable cast iron cranks must have their journals heat treated to be sufficiently wear resistant. The heat treatment is thick enough that I don't believe they need to be retreated with a light regrind, but a large cut requires retreatment.
Ford invented the crankshaft grade of nodular iron in 1951 and has only used nodular in their iron cranks since. Nodular cranks are not heat treated, as the journals possess both strength and wear resistance without heat treatment. This makes nodular cranks cheap to produce. GM and Chrysler used malleable iron in most cases, forged steel in other cases, until Ford's patent expired and the industry has since switched over to nodular iron.
A forged crank shouldn't require nitriding in most applications.
December 19 2008, 5:35 PM
A common forged crank is always heat treated, whether Ford, GM, or other. The "medium carbon steel" forgings have their journals heat treated to increase hardness to prevent bearing scuffing, but I believe the whole crank surface is part of the heat treatment to prevent bending. Nitriding is optionally done in addition to this on medium carbon forged steel cranks used for certain types of racing, though my research is from long ago.
I am unsure of journal hardening for "alloy steel" forged or "alloy steel" billet racing cranks, whether regular hardening or nitriding is required. I know nitriding is sometimes done to alloy steel racing cranks.
