dourvin rocker arms
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default dourvin rocker arms

    Rather than hijack a for sale thread, I thought i'd ask start a new thread on rocker arms here.
    I just grabbed a magnet and headed out and checked a selection of cars and heads.
    The fuego and r25 have steel arms.
    the r21 arms I checked have alloy arms.

    Whats with rocker arms, Alloy/vs steel??
    Is there a difference in their application and performance???

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    I never really gave it any thought before, apart from feeling proud as punch when i lift my rocker cover and admired how smicko they look.
    The r21 top end is prety noisy compared to most fuego's. I wonder how much the alloy rocker arms contribute to this??


    Jo

  2. #2
    1000+ Posts Haakon's Avatar
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    Alloy rockers with hydraulic lifters in them from a late Douvrin V6 are the ones we want - that shuts up the rattly top end these things all have nicely

    These are pretty low output/low stress motor - I seriously doubt there is any noticeable difference in performance.
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

  3. #3
    Fellow Frogger! gsmack's Avatar
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    my understanding is the lighter the better for high revving engines reduces the possibility of valve bounce L

  4. #4
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    Rather than hijack a for sale thread, I thought i'd ask start a new thread on rocker arms here.
    I just grabbed a magnet and headed out and checked a selection of cars and heads.
    The fuego and r25 have steel arms.
    the r21 arms I checked have alloy arms.

    Whats with rocker arms, Alloy/vs steel??
    Is there a difference in their application and performance???

    I never really gave it any thought before, apart from feeling proud as punch when i lift my rocker cover and admired how smicko they look.
    The r21 top end is prety noisy compared to most fuego's. I wonder how much the alloy rocker arms contribute to this??


    Jo

    Alloy rocker arms are lighter than steel.

    The greater the mass (weight) of an item the more energy is required to get it moving.

    Heavier items once in motion have more kinetic energy (energy of movement) and therefore require more energy than a lighter item to slow down or stop.

    All this energy has to come from the engine. Lighter valve gear = less absorbed power.

    Also, lighter valve gear for the above reasons, is less likely to induce valve bounce.





    The more inertia an item

  5. #5
    1000+ Posts jo proffi's Avatar
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    Thanks for the answers guys.
    It all seems fairly logical, inertia being the main culprit.


    I suspect haakon is right in that the performance of my motor is not exactly going to notice much difference, but at the same time I can see the timing belt will have an easier task with the alloy especialy if I ever get around to fitting an after market ecu and upping the rev limiter a bit.

    After searching the net, I didn't come up with much comparative info between alloy and steel, but some of the guys on the gemini forum swear by the steel, as the alloy rockers crack. I guess thats motor-specific info though.
    Every other hit lead to some really bling looking roller rockers that looked like they came of a 1985 bmx bike.

    Jo

  6. #6
    1000+ Posts Haakon's Avatar
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    If you really want to toy with the rockers, get some Bitsmissing Shagna Ashtron rockers and look at tweaking them to fit.

    Not only are they hydraulic, they are rollers as well. And alloy. I have heard they can be made to work on the Douvrin.
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

  7. #7
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Haakon View Post
    If you really want to toy with the rockers, get some Bitsmissing Shagna Ashtron rockers and look at tweaking them to fit.

    Not only are they hydraulic, they are rollers as well. And alloy. I have heard they can be made to work on the Douvrin.
    For the dummy, how do hydraulic rockers work??


    Jo

  8. #8
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    Default Rockers with inserted bronze bearings - not as good?

    The only thing that I can add, is that the steel on steal rockers don't seem to cut into the Fuego rocker shaft with excessive wear, but on my old 68 Toyota Crown motor, the rockers had bronze bearings on the rocker shaft and they cut into the rocker shaft so much I had to replace the shaft. After the second replacement, I was considering turning the steel shaft 180 degrees with the other side bearing the pressure.

    The wear was very deep and this caused problems with an accurate setup for the tappets.

    Other than that the Toyota was remarkable for the small cost of operating it over the many years that I had it from new.

    I have often wondered about the wisdom of having bronze bearing surfaces in that area. Conventional thought of course is that bronze to steel should be ideally matched - but not in that motor.

    Very little wear on the rocker shafts of any Fuego's I have pulled apart..

    Ken

  9. #9
    Demannu-facturing! Demannu's Avatar
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    The change from steel to alloy rocker arms happened sometime in either the second half of 1987 or the first half of 1988. Haven't quite got it down to any more detail than that yet.

    Yes, the aluminiums weigh alot less, despite being much bigger and chunkier.

    The PRV 3 litres had hydraulic lash adjusters, but are very expensive to replace when they wear out.

    I adapted a set of TS Magna rockers with hydraulic lash adjusters and roller followers to fit a PRV piccolo tube, but you need a different profile camshaft to work correctly, which was never available on a PRV and after the trouble people have had having any camshafts made for them, let alone an untrialled profile. So I ditched the idea. Probably still have the rockers somewhere. The Magna ones are still steel, though.

    I have replaced my ZDJL rockers with alloy items from a later ZDJL. I will be replacing the hydraulically adjusted ones in the 3 litre PRV with manual adjustment alloy ones too.

    Hydraulic lash adjusters at high RPM can cause the oil to foam and get air bubbles in the adjusters, increasing the potential for valve bounce by separating the valve from it's spring by what essentially becomes a pneumatic ram.
    Scotty

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