308 aluminum cam gears.....ouch | Page 2 | FerrariChat

308 aluminum cam gears.....ouch

Discussion in '308/328' started by Newman, Sep 21, 2021.

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  1. Martin308GTB

    Martin308GTB F1 Rookie

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    Yeah! Do you mean like this on one of mine? I have an OEM steel set now. Peace of mind.

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    Best from Germany
    Martin
     
  2. dave80gtsi

    dave80gtsi Formula 3
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    The aftermarket adjustable feature allows for easy and simple fine tweaking of the sprocket while the belt is on the car. The alternative is to remove the belt, advance the indexing dowel one way or another, and then reinstall the belt and see how close you have it this time.

    In theory one can remove and install the locking index dowel with the belt still on the car. But in my experience the dowel would not easily push into any alternate and previously unused cam timing holes. I've had to 'open up' the new dowel hole in the cam end with just a very light pass using a round file, likely removing minor manufacturing flash and/or years of road grime and debris.

    So, the aftermarket sprockets makes what can be a bit of a fiddly alignment job far easier to do, and with a finer degree of accuracy the first time.

    Just as a point of reference, my 1980 #33589 2Vi September 1980 car had OEM plastic sprockets. That was yet another one of the reasons why I went aftermarket with this kit in the first place.

    DM
     
  3. Newman

    Newman F1 World Champ
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    Correct, the belt was still on, I would say the timing cover kept it and the pulley from coming off completely.
     
  4. Newman

    Newman F1 World Champ
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    Yours are steel being a QV. Ive seen only a few boxers with plastic gears but 78-82 308's seem to run the plastic ones for the most part.
     
  5. Newman

    Newman F1 World Champ
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    Not installation error. Bolt was tight, lock tab is on properly. The gear failed plain and simple and the amount of holes in a critical area is a factor, no question in my mind. Cant go wrong with steel, you can still buy them new and the belts dont need a modern tooth design to provide reliability. There are literally millions of cars with this tooth design in use and on a boxer running 4 more valves per bank uses the same belt as the 308 and they dont fail either.

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  6. johnk...

    johnk... F1 World Champ
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    Looks like the pulleys were cast and suffered a brittle failure. With the nut it appeared that only the holes near the pin sheared. But, WOW, all the inner hole "ribs" failed.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Amazing that that didn't end in more grief -- you can see how the pin in the cam "moved" over two holes in the sprocket retarding the cam by ~45 deg.
     
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  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    So when you put the 308QV steel sprocket on a 308-2V cam do you have to bore out the center hole, or is it a direct fit (or are you using something other than a 308QV steel sprocket)?
     
  9. smg2

    smg2 F1 World Champ
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    Fascinating...I still don't think there's enough resistive force in the valve train to shear the pulley. Something obviously went wrong.

    Thanks for update and pics.. The witness marks are interesting...
     
  10. Newman

    Newman F1 World Champ
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    When I order pulleys I ask for 2V parts, my understanding was the QV didn't fit and I've never tried.
     
  11. Newman

    Newman F1 World Champ
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    I agree it wasn't sheared. I would say flexing as its being constantly pulled down and to the rear from the belt tension. That and a flaw in the material? Something like this doesn't happen with steel gears.
     
  12. dave80gtsi

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    It’s been a couple of days now since the last post in this thread, and before it disappears deep into the archives, I’ve been struck by something which (to me, at least) is quite curious.

    Reading thru the thread, it seems to me that there have been three (3) different topics, all intermingled. The first two:

    1) Pros / Cons: Round tooth aftermarket vs. squared tooth OEM belts, and:

    2) Pros / Cons: Plastic vs. aluminum vs. steel raw material for the cam sprockets.

    For both of these topics, I believe it is fair to say that different posters (all of whose opinions and experience I very much respect) can have different thoughts. Perhaps it is best to acknowledge that reasonable folks can agree to disagree up to a point, and to leave it at that.

    But it is the third topic which I believe merits a bit more focused discussion:

    3) The wide variation in the quantity and location of the various sprocket’s dowel indexing holes.

    To review, one of the posters here showed a picture of an OEM sprocket with three (3) dowel timing index holes (recopied here for continuity):

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    Then, there are my own personal 1980 OEM sprockets (the plastic ones, not that this matters for the moment) which feature five (5) dowel holes:

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    In my case, I replaced these plastic sprockets with Scott’s aftermarket pulleys which have a seemingly mirror-imaged set of ten (10) holes:

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    And finally, another poster showed a picture of a sprocket, noted to be from a 348 / TR, which features thirteen (13) holes:

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    Thus, we have identified at least four (4) variations in the number of sprocket dowel timing index holes.


    Taking a picture of one of my spare cam ends, one can see that there are three (3) dowel indexing holes, each of roughly 6 mm diameter. But opposite of these, there is a single hole which is about 5 mm in diameter:

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    This leads a curious person to wonder:

    a) It is easy to believe that the initial 3-to-5 sprocket dowel hole transition might have been instituted in order to give the engine assembly line technicians a bit more options.

    b) So, if we accept for the moment that five (5) holes is the “ideal” sprocket hole number, then how to explain the ten (10) holes in the aftermarket adjustable sprockets? In fact, one could easily be forgiven for thinking that just one single hole here could have sufficed, and that any needed timing tweaks could be readily handled thru the sprockets unique +/- 10 degree adjustability feature. So maybe even the “standard” five (5) holes might have been too many?

    c) But the real head-scratcher for me is to try to get a handle on the need for the thirteen (13) hole sprocket flavors. Granted, I don’t know 348 / TR models very well, but maybe those models use a pair of locating dowels instead of just one, thus requiring additional holes on the opposite side? How else to explain this many holes? It is very easy to see how this large number of holes creates a relatively weak section for the sprocket, and if the original OP’s aluminum aftermarket sprocket mimicked this design, then the failure mode as has been noted seems inevitable.

    d) Any good reason why the endplate of the cams themselves has that extra single odd 5 mm thru hole opposite the set of three (3) dowel indexing holes?

    Thanks - DM
     
  13. Steve Magnusson

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    #38 Steve Magnusson, Sep 24, 2021
    Last edited: Sep 24, 2021
    The early 3-on-3 hole pattern gives an adjustment resolution of 2 deg. They went to the 3-on-5 hole pattern to give an adjustment resolution of 1 deg.

    As I already posted, the later 3-on-13 (or whatever) hole pattern still gives the same 1 deg adjustment resolution as the 3-on-5 hole pattern, but doesn't require the Mechanic to change the belt-to-sprocket relationship in order to achieve that 1 deg adjustment resolution (like is necessary with the 3-on-5 hole design). With the 3-on-5 hole design, you don't just slap on the belt, and a pair of holes line up when the cam is in the right place -- you also have to pick the right place for the sprocket relative to the belt. With the 3-on-13 hole design, you can just slap on the belt, and a pair of holes will be lined up when the cam is in the right place (regardless of the sprocket's position relative to the belt).
     
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  14. Brian Harper

    Brian Harper F1 Rookie
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    I need help understanding this. Why does having 13 holes in the sprocket help with lining up with the three holes on the cams? Are you saying that you just don't have to be careful at all putting the belt on the pulley because half of the pulley has holes in it? (That part seems like the easiest part of re-assembly and cam timing by far!) Or that actually finding exactly the right pair of aligning holes is also somehow easier? I don't see how that would work.
     
  15. smg2

    smg2 F1 World Champ
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    The 348 is one belt for both banks and the back side drives the water pump. Yeah... Strange. The ring of holes makes it easier when juggling all the cam positions at once.
     
  16. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #41 Steve Magnusson, Sep 25, 2021
    Last edited: Sep 25, 2021
    Obviously, so do I ;). My mistake -- what was in my mind was the 348 and 355 designs where they increased the number of holes in the sprocket and in the cam to give an adjustment range (just using the holes without changing the sprocket-to-belt relationship) that gives a fine resolution and has a total range exceeding 1 pitch distance of the belt:

    348
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    355
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    That TR sprocket (with the added holes) is also used on 512TR and 512M where the SPC pics show the cams have 4 holes (even though the 512TR WSM only shows 3) -- but I don't have enough information about those to comment. I will say that the text in every Ferrari WSM about this is pretty darn thin on any real explanation/description.
     
  17. Brian Harper

    Brian Harper F1 Rookie
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    Ok, that makes sense to me. My only other DOHC engine experience with adjustable cams was in an old Alfa and it had tons of holes. I think 16 on one side and 15 in the other or something like that. It seemed way easier to manage than the 308 system. And all those holes add lightness. C'mon Ferrari!
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  18. pshoejberg

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    #43 pshoejberg, Sep 26, 2021
    Last edited: Sep 26, 2021
    Maybe there is a reason why it takes a team of several hundreds highly skilled engineers to keep a formula one team or a car manufacturer development department in business. I have always wondered what make people chose to swab out perfectly working and field proven super critical equipment with fancy shining and colorish stuff using the argument that it is easier to adjust? Maybe I misunderstood something here? We all know that in a few years ahead, when the 308 has become even more collectible than it is now, all that stuff will be binned and original spare parts will be in high demand. I fully accept that every one can do what he or she likes but it is never as simple as it seems. I can understand that lack of original spares or well known trouble components like the plastic cam gear can result in needs for alternative spare parts but due diligence is required. Sorry guys I couldn't resist.

    Best, Peter
     
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  19. mwr4440

    mwr4440 Five Time F1 World Champ
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    For those who have never timed a 3-hole(cam) / 5-hole(pulley) 3x8 before, ... it is VERY PAINFUL.

    It can take MANY ITERATIONS to get just one cam in place to the WSM specified +/- 1° crank.


    THE distance between the holes in the cam and the holes in the pulley, and where they are placed in each,

    AND the relationship between the belt drive gears and the cams,

    AND the degrees between the teeth on the pulley and valleys on the belt (and vice versa),

    ALL have interlinked mathematical relationships with each other.

    Move any one, cam, pulley, drive gear, dowel, tooth, belt, just one position, and you can screw up the WHOLE THING UP to the point the car may never run again, or never run 'right' again, until PROPERLY readjusted by a Competent Tech at North of $200/hr.

    Did I say it can be PAINFUL?


    Even IF you have the Timing Matrix Steve M. posted here years ago, if you can't keep the math straight, You Are Screwed (I couldn't, so I went thru over 100 trys before I got all 4 cams Indexed. Trust me, You don't want to do that.).

    DID I SAY ..... 'PAINFUL?'


    There is a 'Trick' to it, to do it quickly and easily, but those few who are 'in-the-know' AIN'T TALKING. And I don't blame them.


    So, AFTER you gone thru some pain, as you should for 'a great car story's sake' if nothing else, PM me and I'll send an automated, graphic spreadsheet I developed with Expert Help from Steve M above, that you can use to Index each cam to +/-1°* Crank, in just two spins of the motor.

    Yep. Just two.

    1st Spin, to see where the 'event' happens,

    [Put that one data point into the spreadsheet, Hit RETURN, and then do EXACTLY what it Graphically SHOWS you to do.]

    2nd Spin, to check your work.

    NEXT CAM.

    NEXT CAM.

    NEXT CAM.

    DONE.


    Total elapsed time: less than 60 minutes. :)




    * - With a little forethought and effort one can get much closer to 'PURRRRRRRFECT' Timing than +/- 1°. All my valves are within about 1/8th degree of 'Perfect.'

    A BIG Degree-Wheel helps.** ;)



    ** - Guess the distance between these two lines:

    | |


    And these two lines:

    | ...................................... |




    Yep. You guessed it.
    The distance is the same between the two sets: 1°
    :D
     
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  20. derekw

    derekw Formula 3
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    A couple of my plastic pulleys had fence cracks that showed up with dye penetrant. I seem to recall they used plastic to reduce noise (and they never expected the cars to last this long!)

    For this case I think Scott covered the essential things early on. The pins don't (or at least shouldn't) transmit any of the torque-- the friction from a correctly tightened pulley bolt does that. I think the stretch in that bolt would absorb the heat expansion of even an aluminium pulley. That leaves catastrophic failure due to a sudden overload or fatigue if the cyclic stresses-- bending from belt tension and torque from the rotation combined with stress concentrations from the geometry (the round pin holes and any notches or surface imperfections.) Medium carbon steel and 7075 aluminium have similar stress and fatigue properties but 6061 (which is more common and cheaper) is about half as strong. The anodising gives a hard surface which resists wear and corrosion but slightly lowers the fatigue strength at higher stress concentrations due to the brittleness of that surface layer. If the design or material is borderline (like a weaker alloy or poor quality material) then anodising may actually shorten the fatigue life.

    The pulleys I had made are 7075 and have 12 holes which was well below critical fatigue limits but this one appears to have 15 which might be pushing it if you are using a weaker alloy like 6061. I still suspect something else was at play (bolt loosened, over-tight tensioner, bad material etc.) It would be interesting to know the mileage on the pulley and where it came from.
     
  21. mwr4440

    mwr4440 Five Time F1 World Champ
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    #46 mwr4440, Sep 27, 2021
    Last edited: Sep 27, 2021
    Derek,

    By looking, I knew it wasn't yours as I think I own all your iterations. [I'm a 'Parts Collector' OEM and Indie.]

    Very GLAD You posted as to your Specs and process.



    I own Scott's (SMG) Too.


    And a steel set and a One-Piece aluminum set outta Berlin.
     

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