Crankshaft types and differences

Discussion in 'Engines' started by Brian.G, Jan 1, 2010.

  1. Brian.G

    Brian.G Forum Member

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    There are three different manufacturing processes used in order to make crank shafts.

    1. Casting.

    2. Forging.

    3. Billet machined.

    The first two are common in the Volkswagen/Audi range.
    The last one being more common in super cars or race cars.

    Questions often arise as to which type crank shaft is fitted to an engine you have opened given the fact that both 1 and 2 are fitted to power plants we're used to dealing with.

    Ill go through them all below, how to recognise them, how they are made, why the manufacturing process makes them recognisable, and the hardening process carried out for each type of crank which can also effect appearance.

    Ill also go through why one is better than the other and why.

    1. Cast Cranks.

    These are around for a long time and are found In a lot of engines and in both petrol and diesels.
    As the name suggests these are cast and made from Malleable Iron. The shape being defined by a sand mould as with many other engine parts.
    These are pretty cheap to make and hold up fairly well too so they are a common choice for manufacturers.
    A sand mould is made comprising of a top and bottom half, a pattern is made in wood or other material and this forms the required shape the mould halves contain once they are brought together. The molten metal flows into this mould relying on gravity alone.

    Both flat plane (single plane) and cross plane cranks can be made this way fairly easily.
    A flat plane crank is one where the journals are 180 degrees apart common in all in-line four engines.
    Therefore only two mould halves are needed to make them as the pattern can be withdrawn from the sand mould without locking. This leads to fairly quick production times.

    A cross plane crank on the other hand needs a mould of multiple parts because the journals and counter weights are not symmetrical either side of the parting line(where both mould halves meet) Therefore withdrawing the pattern from just two halves would be impossible.
    This isn't a major issue all the same as once the moulds are figured out production is just as fast as for a single plane crank.

    Here is a single plane crank common to in-line four engines. Notice how it is symmetrical so only two moulds halves are needed to cast it. It has just one casting line along its centre.
    [​IMG]

    Here is a cross plane crank common in V engines. Notice the journals are 90 degrees apart. This makes a two mould cast impossible as the pattern could not be withdrawn from the two mould halves so a more complex mould build is needed. On older cast cranks of this type many different parting lines can be seen in different locations on the cranks due to multiple moulds being used to build the finished mould.
    [​IMG]
    Its pretty easy to tell if your crank shaft is cast by looking at it a bit closer.
    On a cast crank you will see the parting line easily. This line is created where both mould halves come together.
    The line will be easy to see, defined, and approx 2mm wide. On an in-line 4 flat plane crank it falls on the centre line of the crank also.
    I may as well mention grain structure now at this stage too, metals have grain structure, the easiest way to describe this without going into too much boring detail is to think of each grain as an arrow.
    When a part is cast such as the crank above your spilling in all these arrows into the mould at once, and under atmospheric pressure. This as you can imagine leads to slight chaos within the mould. The arrows have no order, direction, or organised layout. They also aren't as close to each other as they could be. This in turn effects the over all strength and properties of the finished crank. But it is a quick process and the crank can be cast to pretty much near its final dimensions so minimal machine time is required.
    Mould manufacture is also fairly cost effective with this process.

    Below is a close up of a VW cast crank, notice the defined parting line and slightly rough texture the metal has taken when poured into the sand mould.

    [​IMG]

    And a close up on the counter weight showing sand like texture.

    [​IMG]

    And the picture below showing the micro structure. Notice how the carbon has clumped in some places, and also the general randomness of the material itself.

    [​IMG]

    Even on a cut cast crank I have you can see the carbon present on the cut face. This is the main reason why cast has such good wear properties as it is self lubricating to agree due to this carbon/graphite.

    [​IMG]


    Cast cranks can be flame hardened to improve wear resistance in particular areas.

    Flame hardening involves aiming gas flames to particular areas which require hardening.
    This is sometimes done on a jig having multiple flame jets aimed at, in this case the various bearing journals.
    Once the desired temperature is reached the crank is then quenched in molten salt and oil.

    Water is rarely used in this direct contact case as it extracts the heat so fast as cracking may occur.
    After flame hardening the casting then consists of a hard, wear-resistant outer layer of martensite and a core of softer grey Iron.

    Flame-hardened castings are stress relieved at 150 to 200C after quenching to remove any tension caused from the quenching process. It is at this stage that the final journal grinding can occur.

    Below is an example of a flame jig, although it is for a camshaft the principles are the same. Aiming the jets at just the bearing areas ensures that the crank still remains ductile in other stressed areas.

    [​IMG]

    That pretty covers the basics of cast cranks and how to recognise them, now onto forged cranks.

    2. Forged Cranks.

    These are a more robust crank than a cast crank for a few reasons.
    They are more commonly found in higher stressed engines and come standard in some 16v engines and almost all of the 1.8T engines. I do believe they feature in the new fsi engines too, although I have not yet got the pleasure of getting my hands on one>yet.

    A forge crank is made in a totally different way to a cast one.

    A set of dies are machined to the approximate shape of the crankshaft as below.

    [​IMG]

    These dies sit in a very large hydraulic press having a clamping force of many many tons.

    A hot bar approximately 150mm in diameter is placed onto the bottom die and the dies are closed.
    The bar is of high grade steel alloy containing all the various metals needed in order for the finished crank to fulfil its job.
    One benefit of this is the metal does not need to have certain properties required for casting, fluidity when molten, etc.

    Once the dies are closed the metal is squeezed in very tightly, this has the effect of making the metal more dense, packing the arrows closer together if you like, and also given the fact the entire bar is pressed into the shape of the dies the grain structure also follows the shape of the crank throughout too. The material is then both compacted and aligned better than with the casting process.

    Below is a set of forging dies for a flat plane crank, these dies are extremely costly to manufacture, one of the reasons why forged stuff is dearer than cast counter parts.
    Notice the four posts at the corners, these act as position and as limit stops.
    [​IMG]
    Here you can see the dies fitted to the press and the heated blank within.

    [​IMG]

    The rough forging being withdrawn.

    [​IMG]

    The dies are pressed together until the limit stops on the dies come into contact, once this happens the blank has been completely pressed and any excess is squeezed out the gap between the dies. It is this excess metal, or flash that makes a forged crank very easy to recognise. This flash is quite thick, sometimes as much as 10mm, as a result it has to be ground off before any finish machining can be done. This so called part line then ends up being quite wide and can be recognised instantly over a cast cranks faint part line.

    Here is a better view of the excess metal where it has been pressed out once dies were full.

    [​IMG]

    The grinding of this flash also adds to the cost of a forged crank.

    On a close up of a forged crank I have here the wide flash line can be seen easily.
    One of the main tell tale signs of a forged part.

    Forged on the right.
    A forged crank will also have smaller counter weights for the simple fact that the material is more dense and therefore heavier than that of the cast type.

    [​IMG]


    And the picture below showing the micro structure. Notice how its tighter and more organised looking than the cast shot.

    [​IMG]

    These type cranks are also hardened like the cast types but a different process is now used.
    Its known as Induction hardening.
    Its straight forward and a quicker and cleaner way of doing it as opposed to flame hardening.

    A coil is placed around journal. Current is passed through this causing the journal to heat up, once at the correct temperature coolant is then passed though the coil assembly and it rapidly cools the metal in this particular place causing hardening of the metal to a pre-set depth as with flame hardening.
    This also eliminates the danger of either overheating or burning the surface of the metal as with a flame hardening.

    [​IMG]

    Induction hardening also causes the surrounding journal material to take on colours, similar to the colours sometimes seen when a crank has been heated due to lack of oil.

    This colouration is a characteristic of this hardening process and can be alarming when seen for the first time on your own engine.

    The colouration can be seen below.

    [​IMG]

    Of course, forging has its limits too, single plane cranks can be forged easily as only a top and bottom die are needed to stamp a single plane crank as shown again below.

    [​IMG]

    A cross plane crank due to its 90 degree journal positioning cannot be stamped using the normal two die method so a change has to be made to the hot forging before it is cooled.

    The cross plane crank is stamped as a normal single plane crank in the beginning, that way it can be removed from the dies and a simple two die set up works fine.

    Before the forging cools the crank is placed into another machine which grips the big end journals and turns them 90 degrees and into their correct positions as shown below.

    [​IMG]

    Doing so this has the effect of twisting the already formed grain structure at the main journals.
    Although single plane forging is extremely tough, this is sometimes frowned upon as causing a disrupted or weak spot in a cross plane forging.

    This is where the billet crankshaft comes in.
     
    Last edited: Jan 1, 2010
  2. Brian.G

    Brian.G Forum Member

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    3. Billet Cranks.

    Billet cranks are the best type of crank you can have in your engine if you want to get the most from it.

    They start off again as a very high grade steel containing all the correct alloys needed to meet the demands. 4340 steel is normally used which contains nickel, chromium, aluminium, and molybdenum amongst other elements.

    The Steel blank is then forged to align the grain and compact all the molecules closer together as in the case of the forged crank.

    The dense blank is then ready for machining.

    [​IMG]

    These cranks are the dearest of all for many reasons.
    The main one being the amount of time needed to machine them, and also the fact that approximately 70% of the billet will end up as swarf.

    Here you can see a billet crank in various stages of production, it is from a Ferrari.

    [​IMG]


    Its pretty easy to tell a billet crank from any other, for a start it has no part lines or wide flash lines. They are usually very nicely machined to very exact specifications.

    [​IMG]

    [​IMG]

    They also require minimal balancing due to the uniform make up of the material and the extremely accurate machining carried out throughout.

    Billet cranks also have one major manufacturing benefit and that is the blank.
    You can xray the blank and carry out any other tests necessary during machining. That way you know your going to have the perfect crank once your done milling containing no irregular zones or pockets.
    This is not watched as close with cast or forged cranks.

    Machining is also a more controlled process over-all so any internal stresses or defects get ironed out through stress relieving during and up to the final machining.

    These type cranks are normally hardened at particular areas such as the journals through a nitriding surface hardening process.

    The crank is finished machined to the correct tolerances before this begins.

    The journals are heated in the presence of ammonia gas, the nitrogen in the gas soaks into the steel.
    The alloying elements in the crank form nitrides towards the surface and form a hard skin around the journal.
    This is over all an easier process on the crank than the other methods and your not grinding away any of it after.

    Care should be taken on regrinding a billet crank because this hardened layer is not as thick as with the other methods.


    Which one is better and why.

    Cast.
    Forged.
    Billet.
     
    Last edited: Jan 1, 2010
    HPR, Toyotec, infinity and 1 other person like this.
  3. danster Forum Addict

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    Excellent info there!:thumbup:

    The pics really show the difference between the cast and forged cranks.

    I found the 2.0 forged cranks are a couple of pounds or so little lighter than the cast ones.
    I weighed them when i was building a 2E 8v and an ABF 16v. Both were standard and not ground or lightened in any way.
    I have also used the forged one out of a Audi 6A 2.0 16v as i did not need the trigger wheel and presume a 9A 2.0 16v would be the same too.
     
  4. Brian.G

    Brian.G Forum Member

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    Indeed, they are a touch lighter due to them being more dense, therefore they can be made slightly slimmer but have still hold the strength.:thumbup:

    I have a bit left to fill in later on why one is better than the other, I want to keep it fairly simple and not turn it into a metallurgy session which can be a bit tiresome to read.
    It should still give a good insight to the different types and processes all the same.

    For anyone interested it was this thread that nudged me to do the above.
    http://www.clubgti.com/forum/showthread.php?t=204712
     
    Last edited: Jan 1, 2010
  5. 2dubnick Forum Junkie

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    great thread, only just had a skim read now but look forward to a good read later.

    Cheers Brian:thumbup:
     
  6. Neal H Forum Member

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    Well done Brian. Interesting and informative read. What would be useful would be to add which engine codes used which type of crank...
     
  7. Brian.G

    Brian.G Forum Member

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    Yes great idea, could be done here or in another thread? Maybe here as it would be kept altogether then? I dont know, up to the mods.

    The few Im aware of below.

    S=Short nose
    L=Long nose.

    With some work a long nose 06A crank can be made to fit the 058 block.


    1.8l 8v PG > Cast(s)
    1.8l 8v PB > Cast(s)
    2.0l 8v 2E > Cast(s)
    1.8l 16v KR > Cast(s)
    2.0l 16v ABF > Forged(s)
    2.0l 8v ABK, 3A, AAD, AAE, ADW > Forged(s)
    2.0l 16v 6A, ACE > Forged(s)
    1.8l 20vT AEB > Cast(s)
    1.8l 20vT AUG > Forged(l)
    1.8l 20vT BAM > Forged(l)


    Please add more if you know of any:thumbup:
     
    Last edited: Jan 2, 2010
  8. Brian.G

    Brian.G Forum Member

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    Edited, thanks a lot:thumbup:
     
  9. RobT

    RobT Forum Junkie

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    lovin this, nice one

    my lad has been making forged plastacine fish since christmas day :lol:
     
  10. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    1.8l 8v PG, 1H > Cast(s) 0261051013E
    1.8l 8v PB, GU > Cast(s) 0261051013 early supeceded by 0261051013E
    1.8l 16v KR, PL > Cast(s) 0261051013E
    2.0l 16v All > Forged(s) 053105101H
    2.0l 8v ABK, 3A, AAD, AAE, ADW > Forged(s) as above.
    2.0l 8v AGG, ADY, 2E > Cast (058 block)053105101K, Seat part #'s suggest use ABF unit.
    1.8l 20v ADR, > Cast(s) 026105101R ( manual) 3B Passat/8D A4
    1.8l 20v AEB, APU > Cast(s) 026105101R ( manual) 3B Passat/8D A4
    1.8l 20vT AGU, ARZ, AUM, AUQ, APX,APY, AMK, BAM > Forged (06A block) 06A105021
    1.8 20v AGN > Forged (06A block) 06A105021 Golf Mk4 N/A
     
    Last edited: Jan 2, 2010
  11. Brian.G

    Brian.G Forum Member

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    Fantastic!
     
  12. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    2.0 20v ALT > Forged 06A block 06A105021E 3B3 Passat and 8E Audi A4
    2.0 16v FSI AXW > as above
    2.0 16v TFSI early 06A105021E then 06A105021S and 06A15021AR

    Vortex thread with pictures what the TFSI cranks look like.
    http://forums.vwvortex.com/zerothread?id=3517106
     
  13. Brian.G

    Brian.G Forum Member

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    Great stuff, coming along well. Actually, I wonder could these be tidy'd into some form of table or something?
     
    Last edited: Jan 3, 2010
  14. mark25 Forum Junkie

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    I thought the crank in the Passat PB engine was different to the rest of the PB cranks.
     
  15. TheSecondComing Forum Addict

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    I have a 2E engine in the garage with a forged crank and rods, for some reason? Maybe a replacement?
     
  16. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Might be although Seat says that some may have the forged unit found on 16vs
     
  17. Hotgolf

    Hotgolf Paid Member Paid Member

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    I've had 2e cranks here nearly identical to valvers. They seem to swap and change every-so-often.
    The early cast 20v crank I borrowed not long back was the best cast cranks I'd seen in a long while. Totally even, with only the small amount of balancing required.
     
  18. danster Forum Addict

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    May be worth noting which cranks come with the trigger wheels, aswell as stroke, forged or cast, long or short nose.
    Heard the trigger wheel cranks are more awkward to have lightened because of maintaning the face the wheel goes onto.
    Couple of threads going on about the diesel block and crank at the moment and there are options on those cranks too.

    Diesel cranks.

    1Y, AAZ - no trigger wheel, 95.5mm stroke, short nose,

    AHU, 1Z - trigger wheel, 95.5mm stroke, short nose,

    AGP, AQM, AGR, ALH, AHF, ASV - trigger wheel, 95.5mm stroke, long nose,

    There may be a change in the way the timing belt pulley is held / located on the crank nose on some of the TDI cranks. D instead of keyway.

    Not had a chance to double check if these are cast or forged yet. I think cast but not 100%. Let me know and can edit.
     
  19. A.N. Other Banned after significant club disruption Dec 5th 2

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    If poss, it might be worth adding what cars these codes are out of. People know the mainstream ones, but AGR, ALH etc gets me a big fat fail.
     
  20. Brookster

    Brookster Paid Member Paid Member

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    Excellent thread Brian here's some extra info if .

    ABF Crank Standard 92.8mm stroke
    [​IMG]

    1Y Crank Standard 95.5mm stroke
    [​IMG]

    ABF Eurospec Billet Race Crank 92.8mm stroke
    [​IMG]

    All weights are in KG's
     
    Last edited: Jan 5, 2010

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