Crank hardening
 

Hello all.

I'd appreciate opinion on rehardening cranks.

To date, I personally have never seen the need to regrind any 911 crank, as good used are available.

But I do have a stash of damaged cranks now, and good used will run out one day.

Even grinding them may be a non-trivial issue..special wheels etc...

But once ground, do we really need to harden them, with all the hassle of straightening and regrinding onto size..?

David

David,

No, all Porsche cranks can be commercially reground and bearing sets are available from Porsche and others (Pelican). No hardening is required.

Carefully measure and document all the crank dimensions first. If necessary use an independent expert.

Of course exactly who regrinds your expensive Porsche crank is very important. Obviously, size and finish are most important. So is chamfering the oil ports and the journal side radius.

Unless you have someone who regularly (and long term successfully) regrinds 911 cranks, I would supply them with the exact dimensions and tolerances for them to confirm correct. Talk to them. Agree on exactly what is to be done.

Magnaflux is a worthwhile test. Find someone really good to interpret the test. I have never heard of a “cracked” 911 crank and the only broken crank I’ve seen was from where the crank grinder failed to grind the side radius. If the test catches only one problem in 10,000 tests, it is worth it for your engine.

Cleaning the oil passages is an absolute must, particularly the blind passages. I don’t think you need to pull the plugs to achieve good cleaning..

YOU need to be able to independently measure and confirm all the dimensions at least as well as the crank grinder. He needs to know that beforehand. You will get the best work if he knows there is post-grinding inspection by someone else.

A not-uncommon problem is you get a call saying that the first grind didn’t take care of all the problems. Take the crank to your independent inspector for analysis and then return it to the grinder.

Pay them something extra for good work. Make it clear that if they damage your crank, they are responsible. Impress them with the retail cost of a new crank.

There are also some acceptable repair techniques for badly damaged steel cranks. These can be appropriate for still great street engines. Supposedly there are also “trick” processes to apply to the crank. Tread carefully.

Best,
Grady

PS: Rod inspection and reconditioning are other important issues. What about the crankcase?
G.

What a helpful and obviously knowledgeable reply!

Thanks.
And yes, rods and especially cases are the usual suspects in these motors, I agree!

I'd really like to know how and where to drill the extra oiling holes for hi-rpm motors...

David

Hmm, just about everyone else I know of doesn't use reground cranks that are not re-hardended.

-Wayne

Thanks , Wayne.

Do you think this is because of the superior fatigue performance, modulus, or the surface characteristics of the nitrided crank?

Thanks
David

Here is a thread where I showed my method of ensuring the 2&5rods get the oil they need for extended high RPM running (2&5 are prone to oil starvation)

Look here

another equally good method was shown also

Thanks very much, Tim.

I saw that thread.. very good.

What I'm looking to confirm is the drillings in the crank itself please.. I was planning to do more than one main .. but if one is enough I'll just do that.. whcih one?

Kind regards
David

the crank journal between the 2 and 5 rod throws is drilled to intersect the existing oil passage

I thought that the cranks are hardened to a depth that will allow 1 regrind without a problem?

a very respectable machine shop over here that has been regrinding porsche cranks for over 14 years told me that 70-90% of damaged cranks that have come to them for assesment and regrind are cracked from excess heat buildup at the journal. worth getting a proper mag test me thinks!


Andy, UK

Wayne,

I agree; a standard crankshaft is most desirable. If it weren’t for the cost, many would install a new crank at rebuild. I actually would prefer a good used polished crank over a new one.

I disagree that a properly ground, polished, and inspected crank isn’t suitable for reinstallation in a 911 engine. Would I prefer a standard crank – yes. Would I use a properly reground crank – yes. Would I prefer it be properly rehardened - yes.

The issue of hardening is more difficult. Both you and Bruce address that issue in your books. It seems the most important difficulty is reliably reinstalling the oil plugs. I certainly don’t disagree that a properly re-hardened crank is desirable.

What do you think is the best journal hardening techniques? What is hardened, just surface of journals or the entire crank? How much control is there over the process, is there variable hardness? Will regrinding the crank again remove the hardened surface? Will the process make the crank more prone to cracking? Who can perform this task? I have never seen any specs for the aluminum plugs in the cranks. What is the proper alloy and interference fit? Why have there been failures?

Best,
Grady

Grady, the cranks that I have seen hardened have been spun while a flame makes contact on the journals. the journal is heated to the appropriate temperature for a certain duration. This duration dictates the depth the hardening will attain. So no, it is not just the surface. Keep in mind that once the crank is hardened, a finish grind will be done. Once the journal has been heated it is quenched and the process is started over untill a specific hardness is achieved.

It is entirely possible to machine past the heat treatment, but this is where everybody has a different opinion. Does Porsche recommend flame hardening the crank in order to regrind? If not then I would bet that the hardening is at a sufficient depth for all the regrinds.

Yes the crank is more prone to crack when you heat treat because it crates internal stresses. But it is required to provide a durable bearing surface.

As for the rest I cannot say, and as a disclaimer I am not a professional automotive machinist, but I did stay at a Holiday Inn Express last night. :)

it's nice that they treated the surface, but think how many other engines are out there running around with a stock or reground, untreated crank and doing just fine? stock and performance engines. multi-millions.

Most other engines have heat treated crank journals. Its a requirement for a durable bearing surface. The soft nitriding was the cool extra thing that Porsche used to do. If there is another engine running around without it I will gladly eat my shoe.(I should probably start untieing it). Aaron.


BTW John, I love type 2s. I even have a 64 double cab waiting for me to put the floors back in. If you have an ambulance fan switch in your pocket I sure would like one.

There is a chemical solution you drop on the crankshaft journal to see if it has been nitrided. Some Chevrolet steel cranks I have seen do not pass this test. They are usually worn past low limits enough to require grinding.
Nitriding really works on Porsche cranks.
If the journal is really bad, it can be built up by welding. Using two types of welding rod, one for the crank pin and the other , harder rod for the fillet radius. Then nitriding will harden the crank correctly and stress relieve.
This link has some info on heat treating.
http://www.nitrex.com/industries_automotive.ch2

John, are there any other methods (like visual) to see if the crank has been nitrided? My father has a 69 s crank and rods that should have been nitrided at the factory.

Porsche used a process called tennifer treating. Its a cyanide salt bath similar to
GM's tufftriding. It doesnt penetrate very deep (.0003" to .0007")
If the crank has been ground to the 1st undersize, the heat treat would be gone.
I wouldnt be able to tell visually between the untreated crank and a treated.

I did a quick Google on Tuftriding. It seems most companies that do this are overseas. The process must be deadly enough to phase out the many companies that used to do it domestically.

I remember the advantage Tuftriding had over Nitriding was that the heat treatment didn't take as long and the temperature wasn't as high. Elevated treatment temperature tends to induce some bending in the crank. And yes, the treatment depth was only a few thousandths - enough for journal hardness but not enough to survive the next std. regrind.

Sherwood

burn, check www.thesamba.com in the bus parts classifieds for that fan switch. they come up occasionally.

Thanks John W. I will do that.



John D, do you know when or if Porsche has stopped the process? I know from books that most of the early stuff was done, but there is no mention of the later 70s to the present.

I have a call in to my favorite crank grinder,
I will quiz him on this heat treat question.
I believe most new cranks are induction hardened. Induction hardening is much faster and easier to control the results.

Guys,

Thanks for the very informative posts. The people in industry and science can make a great contribution to this Forum.

I can’t find my old Machineries Handbook. Exactly what is annealing and quenching? What is the difference between “hardening” and “surface hardening?”

I assume the hardening process is just as applicable to cam lobes and journals and rocker arm pads.

While I don’t want any of the industry guys to give up trade secrets, I have some generic questions.

It seems like the flame method is somewhat like TIG (Tungsten Inert Gas) welding where the atmosphere is critical. With flame hardening what is the composition of the flame? Does the process have to be in a controlled atmosphere? Are there chemicals transferred from the flame or atmosphere that affect the hardening or is it strictly a temperature-time cycle process?

Does the entire crank (cam, rocker) have to be heated (or cooled) to some specific temperature before the process begins? How long does it take for a crank to equalize (rest) between processes? Can all the journals be treated at once or is it a one journal per day process?

Do some of these processes go further than just hardening the surface of the journals? What is the effect of hardened surfaces on the counterweights, internal passages, etc?

Thanks to John at Elgin, this is a very informative page:
http://www.nitrex.com/iactivefiles/Nitridingmethods.pdf
What are the other hardening processes?

Sherwood: What are the chemical hardening processes that have been driven offshore? Are these processes any better than those available in the States?
Does anyone know of reliable firms that can perform those tasks in Germany, GB, Canada, Mexico, China, etc?


Is there a different process for the 2.0T & 2.2T cast iron cranks from the other forged steel cranks?

What does Porsche supply in the current production engines?

Is there Factory Service Information (current or archaic) available?

Perhaps we should list some of the best re-hardening businesses and the pros & cons of the differing processes.

Best,
Grady

Grady,
I'm assuming EPA regs are making it difficult for domestic heat treatment using the Tuftriding process. Look at the nitriding chart provided by John to get an idea of the waste products as a result of these processes. Perhaps more current techniques are cleaner. I've noticed several companies in the UK offer the Tuftriding service. You can launch a search in Google to get more info. You might even find some domestic companies still doing this; you could also ask some of the Porsche machine shops who/what they use.

There are several surface hardening processes, but all create a hardened surface on the base metal to various depths. You still want a relatively ductile, yet tough interior metal structure. Hardened throughout, the part would be very brittle and would fracture in no time.

Sherwood

Annealing is heating the material up to a specific temp for a period of time so that the material relaxes. It will loose all hardening properties. A forged crank would be annealed after the forging process to relieve internal stress. you would typically rough machined,normalized(heated above the critical temp to gain uniformity), then either flame hardened then finish ground or as John D. has brought up, finish ground then nitrided. Wayne should feel vindicated on the matter of heat treatment when a regrind is done specifically with nitridded cranks.

I will guess that the atmospere is not critical when flame hardening. I saw a history of the beatle on the t.v. . They were flame hardening the mains on a sort of engine lathe. each main had an individual flame pointed at it. It was rotated while it was heated then quenched with oil. Quenching is the temp down past critical leaving the austentite molecules fixed. The process is done until there is sufficient austentite ther to achive the Brinell hardness required. The process was automated and done very quickly. Flame hardening can achieve depths deeper than with nitriding. Keep in mind that you only want a hard surface, when you harden it becomes brittle.

Here is two more links.
http://www.metaltreaters.com/page3.html
Kolene Corp. owns the trademark to the name Tufftriding and from the looks of it may only be able to salt bath nitride now.
http://www.kolene.com/applications/sbn.asp

is there some reason that i cannot think of which stops people from cryo treating cranks??

As far as I know, cryo-treating metal does nothing for surface hardening, which is what you want to achieve on bearing surfaces.

Sherwood

This is the info I have,
all cranks from Porsche starting with the 356 C engines are tennifer treated. This treatment only goes .003" deep and is lost on the first regrind. I recommend nitriding
any Porsche crankshaft that has been ground undersize.
I have seen a few Cryogenic treated camshafts and all have been bent over .050". I do not see a benefit on camshafts
freezing them.


The following link is for Goodson products, they have the chemical to check crankshafts or heat treating. It is called Ni-check.



http://www.goodson.com/g5-bin/client.cgi?G5genie=1;G5button=1;search_button=Sear ch;INVOICE_ID=&item=P5013

Thanks John. I will log that info in my peanut.

Aaron

cross drilling
 

hello guys.

I'm grateful for the excellent information posted..thanks.

To save us reinventing the wheel, please could some kind soul advise me on the best axis to drill the cross-drillings?

On most run rod bearings I have seen, it is the same journal.. that farthest from the ends, which goes.

So I was planning to drill through the adjacent main, and one other.

But what I'm not sure of is what axis to drill on.. ie oriented to, say no1 crank throw.... and whether to drill through both sides of the journal..

Kind regards to all..
David

sorry to open an old post. Im curious if the thoughts have changed on regrinding cranks in the last 7 years?

If you plan on sending out a crank for re-grind, "ring" the crank first.
You hold the crank on your fingertips on one of the counter weights and strike the crank gently on the outside edge of another counter weight.
Do not strike a journal!!!
A good crank should ring like a bell.
A bad crank will sound dull like a "boink".
Fastest way I know to check for cracks.
This does not guarantee a non cracked crank, but it has stopped me many times from spending $$$ that I did not have to spend getting a shop to Magna-flux or Dye-pen check a crank.
My $.02
Bob

Mark,

You can regrind them, however they must be nitrided to maintain durability. Further, they need to be straightened after that process is completed. The only guy I trust to do this critical job is Armando at Marine Crankshaft in CA.

Naturally, one requires oversize bearings and those are not cheap.

In many cases, its far less expensive to source a GOOD used standard crank. :) :)

Cranks
 

Chaps,

I am always surprised about the variety of opinion on the subject of 911 cranks and their heat treatment and the variety of solutions that seem to be advised.

I have put up a few posts on the subject but it doesn't hurt to repeat some of these comments.

I believe that all early cranks were Tenifer treated which is the Trade name of a process known as ferritic nitrocarburising.

The sam process is sold in the UK as Tuftriding and in the USA is also known as Melonite.

There may be some small differences in chemistry but the basics are all the same.

This process was typically carried out in a cyanide bath at around 570 degC.

As has been stated the surface layer is very thin being only a few thou so the influence on fatigue life is modest.

Cranks
 

Chaps,

I am always surprised about the variety of opinion on the subject of 911 cranks and their heat treatment and the variety of solutions that seem to be advised.

I have put up a few posts on the subject but it doesn't hurt to repeat some of these comments.

I believe that all early cranks were Tenifer treated which is the Trade name of a process known as ferritic nitrocarburising.

The same process is sold in the UK as Tuftriding and in the USA is also known as Melonite.

There may be some small differences in chemistry but the basics are all the same.

This process was typically carried out in a cyanide bath at around 570 degC.

This process also known as Salt Bath or Soft Nitriding and is certainly the poor relation of the genuine Nitriding Process.

As has been stated the surface layer of a tuftrided part is very thin being only a few thou so the influence on fatigue life is modest.

There are many claims that Tuftriding can add between 20 and 60% to the fatigue life of a component but this statemnt does show a lack of understanding of the nature of the fatigue process.

The idea of Nitriding is to introduce surface residual stresses that inhibit the initiation of short fatigue cracks and thus significantly increse the fatigue endurance limit of the component.

An increase in life of 20% assumes that the component will fail at some time and cranks need to be designed for an infinite fatigue life. The fact that they do fail in fatige is due to the stoichastic nature of the fatige process or some other manufacturing defect such as too sharp a radius, as has already been mentioned.

Nitriding has a much greater and substantial impact on fatigue life than tuftriding will ever manage.

The scuff resistance offered by both processes is useful but is not at the heart of the process.

I have to say that without deatiled knowledge of the steel used for 911 cranks I wouldn't nitride. Nitriding generally requires a specialised steel with EN40B being a common example but 722M24 and M897M39 are good alternatives. Aerospace materials such as S132 would also be good.

Nitriding non-nitriding steels can lead to brittle surfaces which can spall and flake in a very unhelpful manner.

I am also concerned to hear that nitriding can cause distortion and bending.

Traditional nitriding in a gaseous environment would almost always be carried out with the component being hung and therefore in tension.

A typical heat treatment/manufacturing cycle for a nitrided part would be to rough machine - often from a forged blank, harden and temper to say a T condition, and then machine to a reasonably close tolerance.

I would then excpect the part to be stabalised at 590 degC to allow stress relief and any movement to occur.

the part could then be finish machined and Nitrided at 570dgC with no further distortion.

The white layer produced during nitriding would then be removed form the journal surfaces by grinding and this allowance would be made prior to heat treatment.

I am intrigued to find that cranks are now being induction hardened as a means of improving fatigue life and I would like to see more detail of how this is carried out as i would be concerned that the steels needed may be OK for normal road engine but coul be limited for high rpm race motors.

Certainly a great many road cars now use an Austenitic Spheroidal Graphite cast Iron which has excellent strength ductility and fatigue life.

This material was developed at BCIRA in the UK and I supplied them a couple of fatigue testing machines more years ago than I like to admit.

I would also like to answer a few of the other questions that cropped up in this thread, I know they are old but it may shed a little light.

Flame hardening is a very old technique which was used to surface harden relatively high carbon steels.

The composition of the flame is irrelevant - this idea is to heat the steel very locally and then obtain a queching efffect due to the coduction of heat waya from the surface into the body of the steel. This technique has been replaced by induction hardening which uses an AC field and the 'skin effect' to locally heat the metals surface instead of a flame. The improvenemt in fatigue life offered by these process would IMHO be very limited.

Annealing is a very straightforwad process. All Ferritic Steels are at their most simple an Iron/Carbon Alloy. Iron is only soluble at room temperature to around 0.02%. Whena steel writh more carbon than this cools it form a structure that comprises of iron and iron carbides. The morphology that results depends on the carbon content and the way it was cooled. Steels which have been hot rolled on a mill are often cooled quite quickly and be quite hard, steels which have been cold worked also harden. At around 723 degC steel will begin to change crystal structure from Body Centred Cubic to Face Centred Cubic and the solubility of carbon increases significantly. Depending on carbon content this process will be complete ast 960degC and a new single phase structure known as Austenite will be present. If the material is then slowly cooled, normally by the simple expedient of turning off the furnace and not removing the material until it has reached room temperature, the material will be in its softest condition. ie Annealed.

Quenching takes place by heating the steel into the Austenite range and then rapidly cooling. As the steel tries to change its crsytal structure from FCC to BCC the carbon atoms which have migrated in the crystal lattice prevent this from happening as the tme domain available locks tham into plave (Fick's Second Law of Diffusion and all that) and a very heavily distorted structure results. This is known as a Martensite Reaction.

To give a basic idea a file is a 1% carbon steel which has been fully quenched and not tempered.

Some random heat treatment links:

Abstract from Metal Science and Heat Treatment

SpringerLink - Journal Article
Abstract**Nitriding technology has gone a long way, from the old gas nitriding to the relatively recently developed plasma nitriding. The latter has replaced the process of soft nitriding in the automotive industry based on nitrocarburizing in cyanide salt baths. It seemed that the high toxicity of the initially used compositions for soft nitriding (Tufftride or Tenifer) should have eliminated salt baths from the industry. However, they are still rather widely used. The replacement of old compositions by nontoxic ones has solved fundamental problems of environment protection. Low-temperature nitriding technology also advanced considerably. Salt bath nitriding is a very active process, more intense than that of gas nitriding and nitrocarburizing including the processes of plasma nitriding. The reactivity of the nitriding medium and the final efficiency of the process with allowance for the cost of the equipment have to be taken into account. An additional advantage of salt bath nitriding is the possibility of treatment of stainless maraging steels. The present work is devoted to comparison of the processes of treatment in a nontoxic salt bath and in a gas medium and discussion of the advantages of nitriding in nontoxic salt baths.

This company claims no difference between Tenifer or Tufftriding processes.
cilindri telescopici telescopic cylinders v?rins telescopiques teleskopzylinder

Varioius Melonite Ppocesses as performed by this US company:
Melonite Processing

Hope this adds to the confusion.

Sherwood

Salt Bath Nitriding
 

Sherwood,

I don't think that Dr. Funatani's paper adds any confusion.

Salt Bath Nitriding is very common and very cheap in comparitive terms.

Road car cranks have been salt bath nitirded for years and it is very cost effective compared to Gas or Plasma Nitriding. The great 'intensity' that they speak of means that processing time at tempertaure is short and hence cost, which is all about heating time is low. the current going rate in the Uk is a couple of dollars a pound.

The 'diffusion layer' which relies on a solid solution of nitrogen in the steel is a well known phenomena that has been developed in the new replacements for the cyanide salt baths but I have yet to see any data of the level of residual stress produced or any real fatigue data.

There are some claims that the nitrogen, which diffuses into the surface also produces finely dispersed nitirides and I feel that this is a claim too far. This will only happen if the correct alloy elements with the correct morphology are present as is the case in a nitriding steel. Some nitirdes can be damaging particulalry on the surface of a component.

The introduction of Nitrogen into steel is a common practice and does have some benetfits.

Treating ground and used cranks with this process seems a good idea and always has been.

I would still use EN40B and gas/plasma nitriding if I needed the ultimate performance.

crankshaft materials
 

Some info on the specific alloys and surface treatments used by the factory.

"With the exception of the 12-cylinder engine crankshaft the crankshafts of all Porsche engines which are now (edit Feb 1972) in production are made from heat-treated steel and tufftrided.
This is a surface treatment in a salt bath at 570°C. Our measurements showed an increase of up to 50 per cent of the fatigue strength for tufftrided crankshafts. We could thus replace the originally used chrome-molybdenum steel in our 911 production engines (42 Cr Mo 4) by the less expensive carbon steel (Ck 45). Porsche uses tufftride or 'Tenifer' treatment for camshafts also.
The crankshaft of the 917 engine is made from chrome nickel steel 17 Cr Ni Mo 6, as this shaft has to be case hardened because of its central drive."

"The Development of the Porsche type 917 car" H. Mezger Proc Instn Mech Engrs 1972 Vol 186 2/72.

hardening treatments
 

From 911 WSM
"Subject crankshaft to Tenifer treatment for 120 minutes at 570°C (1060°F) then quench in deoxygenated bath. Following Tenifer treatment polish all bearing journals and running surface A, and ferroflux complete crankshaft."

From 930 WSM
"Rule for the Tenifer treatment in accordance with Tenifer 90 W PN 1053."

From 993 Tech spec book (and 964 WSM)
"Regulation for surface reconditioning: gas-nitro carbonated PN 2063.....Working surfaces of the main and conrod bearing journals polished after nitriding."

Tenifer (nitrocarburizing) is a trade mark circa 1960 of Durferrit Gmbh

In their own words......
"The TUFFTRIDE® process is known in English-speaking and Asian countries under that name, in Europe and German-speaking countries as TENIFER® and in the
USA as MELONITE®.
TUFFTRIDE®, QPQ®, TENIFER® and MELONITE® are registered trademarks of Durferrit GmbH."

This PDF has a great amount of detail on the process and its effects on a variety of materials (including some of those alloys in the post above). Great reading for the engineers and materials scientists...
Durferrit GmbH Tenifer process and properties overview PDF

[QUOTE=jcge;5462434]Some info on the specific alloys and surface treatments used by the factory.

"With the exception of the 12-cylinder engine crankshaft the crankshafts of all Porsche engines which are now (edit Feb 1972) in production are made from heat-treated steel and tufftrided.

We could thus replace the originally used chrome-molybdenum steel in our 911 production engines (42 Cr Mo 4) by the less expensive carbon steel (Ck 45).
/QUOTE]

Very interesting as is the brochure from Durferrit.

Do you know when the crankshaft material was changed?

Looking at the notched bar data in the Duerferrit brochure it seems that the 'salt bath nitrided' CK45 has a notched bar fatigue endurance Limit of about 500MPa, whic is not bad and certainly a significant improvement on the untreated alloy.
It is similar to SAE1045

This information does confirm my thoughts that standard cranks are not suitable for traditional gas nitirding.

Of course if the test had been carried out on smooth rather than notched bars the improvemnt would have been much less in percentage terms.

CK45 has a typical tensile strength of between 600 and 800MPa depending on detailed heat treatment.

42CrMo4 is a much more expensive steel and has a typical tensile strength of between 1000 1100 MPa.

The notched bar Fatigue strength of gas nitrided 42Cr4Mo is typically around 800MPa.

All about money really.

It is lso interesting that the 917 used a 17CrNiMo6 alloy as I would typically describe this as a gear steel. It has a realtively low carbon content so it can be case hardened but straightening it after carburising and quenching must have been a real trick.