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Old 03-18-2013, 02:00 PM   #101
KillerBMotorsport
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^ Yes, but there are so many process variations with heat treating or nitriding that you cannot make a decent comparison unless you want to discuss precific methods (eg; inductive hardening vs. plasma nitriding).
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Old 03-20-2013, 09:02 PM   #102
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Originally Posted by eg33GC View Post
Now I'ma cognitive neuroscientist, but isn't the theory of crystalline structers more partial to a proper heat treatment being more uniform, and therefore the theoretically safer way of expecting toughness at the journals? Isn't nitriding susceptable to materials variation and process control?
Correct! This is the reason that my nitriding is done in batches of same size and material cranks. They are then lab tested to varify that they were cooked correctly

I only do gas nitriding by the way.
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Old 03-21-2013, 08:44 AM   #103
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This is a crappy cut/past, but gives you the jist of the different nitriding processes. If you go into other surface hardening processes the quantity of comparisons grows significantly. The problem I found with searching heat treaters is they tend to, be biased and say how great their particular process is great without showing listing the downsides or advantages of other processes.

Process Advantages/Disadvantages

Salt bath nitriding

• Rapid heating and processing
• Ease of obtaining good nitrided
layers on low carbon and low alloy
steels in repeatable production
• No in-process control
• Processes limited to those steels,
which can be heated to higher
temperatures, without losing core
hardness.
• Short processes only
• Requires thorough washing to remove
salt residues which may cause
corrosion
• Health hazard and waste disposal
problems

Ion nitriding

• Simple, mechanical masking of
surfaces to be free of nitriding
• Ease of surface activation through
cathodic sputtering
• Low temperature processes possible
• Short saturation cycles
Problems with temperature
measurement and uniformity
Ease of overheating if not closely
monitored
Results sensitive to part geometry and
arrangement in furnace retort
Requires highly skilled and
experienced operator

Conventional gas nitriding

• Low temperature in comparison with
carburizing
• Simple control techniques
• Controlling parameter: (ammonia
dissociation rate) inadequate for
control of layer properties
• In many cases process produces a
brittle white layer which requires
removal
• Masking requires copper plating or
painting with protective paste
• Stainless steels require special
activation techniques

Controlled gas nitriding

• Ease of operation
• Controlling parameter: (nitriding
potential) has direct correlation with
nitrogen concentration and
properties
• Predictable white layer thickness and
phase composition
• Excellent uniformity of layer,
regardless of part geometry
• No finish grinding required
• Masking requires copper plating or
painting with
protective paste
• Stainless steels require special
activation techniques
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Old 03-22-2013, 04:10 PM   #104
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Nice read here. I'm about ready to start a rebuild after a rod bearing failure. The machine shop I'm working with who specializes in flat engines (Old air-cooled Porsche, Subaru, old VW racing motors) said they don't think there's going to be much longevity difference on a pre-treated crank like my 2005 Legacy GT unit and the newer 09+ nitrided/heat treated ones. They said the main thing is proper clearances, better bearings and proper oil and I should save my money and just have them to grind and polish what I have as long as the damage isn't too deep. They don't charge very much on the machine work so I don't think he's interested in the money.

This is my 2nd rod bearing failure. The first one was on a 2.0L on a dyno with who turned out to be a bonehead tuner and the 2nd one happened because the shop I had build me a replacement engine were convinced they could clean out the original oil cooler.

I don't want it to happen again and I still haven't found any testimonial evidence about the newer cranks actually preventing failure. Are the older cranks made with a better alloy or something?

Last edited by BrandonDrums; 03-22-2013 at 04:26 PM.
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Old 03-22-2013, 06:21 PM   #105
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The treatment isn't going to help spun bearings at all so you won't find that evidence. All they really do is prevent the crank from wearing as much. The harder surface just wears less. For some race teams that would be nice because they don't have to replace the cranks as often. For the majority of builds the owner will realize no benefits. Just grind the crank or buy any new one and don't worry about the treatment. The machinist is right. The clearances are the main thing to have right. Set the rods around .002 and the mains at .0015 and you shouldn't have any issues.
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Old 03-22-2013, 08:52 PM   #106
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^ Well said.

For the most part the the non-heat treated, heat treated and nitrided are all marginally similar. The processes are likely different because of a change in OEM suppliers, costs, or Subaru's environmentally friendly "green" initiative.

Regarless of the crank year or process they all tend to have a soft surface hardness and very shallow surface hardness depth. Since they are designed to run on the super soft OEM bearings this is just fine. Harder higher load capacity performance bearings with higher power output and they wear significantly faster. When a crank is refreshed and further ground even more of the surface hardness is removed which can theoretically increase the wear even faster.

I won't have any data for some time, but significantly increasing the surface hardness to a decent depth will hopefully cut down crank wear so it's not a throwaway item for at least many rebuilds. That's my theory anyway
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Old 03-25-2013, 10:08 PM   #107
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Quote:
Originally Posted by kakarot09 View Post
The treatment isn't going to help spun bearings at all so you won't find that evidence. All they really do is prevent the crank from wearing as much. The harder surface just wears less. For some race teams that would be nice because they don't have to replace the cranks as often. For the majority of builds the owner will realize no benefits. Just grind the crank or buy any new one and don't worry about the treatment. The machinist is right. The clearances are the main thing to have right. Set the rods around .002 and the mains at .0015 and you shouldn't have any issues.
I'll agree (though I wouldn't put those clearance on a road course engine) and that's why my motorsports guys get them. They also have anodized top rings and DLC pins and buckets. The crank surface is also less likely to 'grab' the bearing as it too won't scar. So you will have some 'forgiveness' before it lets go.

I'm completely with Chris on the theory of surface hardness and making the crank a reusable item in a rebuild. I have my lab results from my ion nitriding 'recipe' and I'm excited to see how these test out. As for the OEM side though, you'll see that the nitriding process came along with the lead removal from OEM bearings (and 8000+ RPM on the EJ207)...thus a harder/less forgiving bearing from the factory.

-Micah
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Old 03-25-2013, 10:35 PM   #108
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I own a cup car crank Crower built that was in an engine that spun multiple bearings due to a broken drysump belt. I was able to polish off the bearing material and besides being over heated on two throws all the journals still mic fairly close. I believe its nitrided and the interesting bit was when i was cleaning it with thinner I was able to see hundreds of tiny cracks in the journals all of them (the thinner evaporated from the surface faster than the cracks). The pattern of the cracks looked like manhattan or Iowa depending on your altitude but makes me wonder if the greater depth of hardness froma heat treat or put better the slower change in hardness would be the better way to go as opposed to nitriding?
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Old 03-26-2013, 01:28 AM   #109
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Quote:
Originally Posted by 3MI Racing View Post
I'll agree (though I wouldn't put those clearance on a road course engine) and that's why my motorsports guys get them. They also have anodized top rings and DLC pins and buckets. The crank surface is also less likely to 'grab' the bearing as it too won't scar. So you will have some 'forgiveness' before it lets go.

I'm completely with Chris on the theory of surface hardness and making the crank a reusable item in a rebuild. I have my lab results from my ion nitriding 'recipe' and I'm excited to see how these test out. As for the OEM side though, you'll see that the nitriding process came along with the lead removal from OEM bearings (and 8000+ RPM on the EJ207)...thus a harder/less forgiving bearing from the factory.

-Micah
I actually like .001" mains with king XPG's and .002" on the rods. But you go saying .001 on mains around here and people freak out. For a dedicated racecar I'd probably do .0015 mains and .0025 rods with a 50 weight oil but I kind of doubt it really matters much. You have a lot more experience with the dedicated race cars than I do though so I'm sure you have some data to base your decisions around. I don't get to tear down engines and inspect them often.
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Old 04-03-2013, 10:50 PM   #110
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Can I ask what the older STis used for cranks? The 04-07 specifically? I read through this thread but didn't see any discussion there. Wondering if an older crank is fine to reuse or if it is inferior compared to what is available now.
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Old 04-04-2013, 07:24 AM   #111
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Depends on who you ask. They are all capable of significantly more power than stock. IMO they have similar max capacities, but I would never profess to be an engine builder.
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Old 04-04-2013, 10:29 AM   #112
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Thanks, can you tell me if the older cranks are nitrated, heat treated, or anything else?
Interested in that info, and how they compare to these designs.
I have the crank out now and can look at it if there is anything I would be able to identify visually. The crank is from an 07 STi motor that had an issue with the valves from what it looks like. I plan to reuse the block and crank if I can and likely have RalliSpec build me a "Street Spec" block based on that.
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Old 04-04-2013, 11:36 AM   #113
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Honestly, with the 'street spec' you're going to have other components that will fail before that crank... but again I'm no engine builder
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Old 04-04-2013, 11:44 AM   #114
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Thanks again for your input. That makes sense, I just want to make sure that I'm doing things properly and don't cut any corners in what I am building here because I would really like to do it right and do it ONCE. Not looking for crazy power so it should work out fine, but trying to get input where I can.

By the way, I found my oil pickup tube was cracked when I took things apart, I don't have any evidence to show me that it was a source of the problem but I'm glad I found it and will be adding your pickup tube to my setup when it all goes back together.
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Old 04-19-2013, 11:45 AM   #115
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Quote:
Originally Posted by KillerBMotorsport View Post
Honestly, with the 'street spec' you're going to have other components that will fail before that crank... but again I'm no engine builder
Truth!...to the other parts breaking before the crank. The earlier cranks had different metallurgy from the nitrided cranks. I haven't sent the heat treated cranks out for testing/analysis yet.

-Micah
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Old 05-06-2013, 06:32 AM   #116
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So ran into problem with the crank somewhere along the lines and it's got a wobble. I'm going to put it aside and sort it out for the next engine we build. Manley crank ordered in the mean time to keep the already falling behind schedule from getting even worse.
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Old 12-25-2013, 06:19 PM   #117
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I just built shortblock with a 2011 WRX EJ255 crankshaft. Would it be safe to say it's nitrided? I didn't even think to check if it was nitrided before I put it together. It looks like the 430 model on the first page being black/darker vs the heat treated look.
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