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Thread: 3.9 Rockers - Cast Iron or Alloy?

  1. #1
    Join Date
    Dec 2008
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    3.9 Rockers - Cast Iron or Alloy?

    When I replaced my cam and lifters some months ago and shoved everything back in, I noticed that some of the pads on the rockers were slightly grooved, probably preventing rotation of valves. Nothing I could address then as the RRC is my only vehicle and had to drive it. It's been ok but feeling I should should address things.

    My question is in relation to the available parts - there are listings for cast iron or alloy rockers. What's the difference in functionality and longevity? Also, should I get new pushrods or is this a less critical issue as it is for the cam / lifters in using new parts with old.

    I did search for this but found nothing.

    Thanks.

  2. #2
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    valvetrain components are what is always referred to as a "matched set".

    Unfortunately, you are in a predicament.

    You will most likely need to grind the tips of the valves when you replace the rockers, and you will also need pushrods, and possibly lifters.

    The reason I say possibly lifters, is because depending on the quality of the lifter you purchased (with the cam or separately) they will already have a wear pattern from the ball seat of the pushrod. Certainly the camshaft and lifter base will already have an established wear pattern, but depending on the state of the pushrod/rocker and the preload you may find a need to replace more than previously thought.

    These wear patterns which are pre-existing, will only accelerate any wear on a new components contact point that it is being replaced with. Truly unfortunate for you, as it means head off if the wear is "visible"

    You could by all means simply replace the rockers and hope for the best, but they will soon be stuffed in no time flat, since the wear from the existing components is excessive - there should be no grooves in rockers ever. a slight surface dulling from extremely worn ones is more like normal wear pattern.

    Even so, it is normal paractice to inspect valve stem tips with a high powered loupe and see if there is any abnormal wear / ridges. Anytime you inspect components and fine excessive wear on one part, it's corresponding matching component surface will be afffected.

    From your description, sounds like it is well and truly gone beyond what is considered normal wear and as a result will be a more costly repair than previous.

    Best suggestion is to have an engine builder / machine shop look over it before you rush out buying bits and pieces. Some things might be recoverable, and you may be able to save $.
    Roads?.. Where we're going, we don't need roads...

  3. #3
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    I have rebuilt a few V8 rover engines, mostly obtain parts from UK.
    Both RPI engineering and Turner advise not to use cheap aftermarket rockers.
    The best ones are OEM, standard rover rockers. The contact tips are hardened steel,
    some of the flea bay cheap ones break or self destruct in a short time.
    From RPI.

    Why do the steel rocker shafts wear away and not the all-alloy rocker shafts that run on them?
    As an engine's internal parts start to wear out (cam, tappets and timing gear first), metal particles (swarf) are created and set loose to run around with the oil in your engine. Although your filter will trap most of the larger particles, oil filters (especially cheap or old ones) will not stop this swarf from reaching the vital soft metal components (cam bearings, main bearings, big end bearings and alloy rockers where it soon permanently embeds itself into the soft surface of the alloy and white-metal bearings, turning them into a very effective abrasive surface (the end is nigh). Consider this also, why do steel cranks need re-grinding? Because the white metal surfaces of the big ends and main bearings, with this abrasive quality, soon gouge into the hardened steel surface.

    Our advice for rebuilding this area is to re use genuine rocker arms only once closely inspected or buy new genuine arms. However if re using original genuine arms it is important to make sure that the abrasive quality that they may posses from previous years use and neglect is removed. The easiest way to do this is to simply lubricate some 1200 wet and dry paper and run it around the inside of the rocker arm lightly. This is not to remove material but in effect off a light hone to the surface to remove any sharp shards of swarf.
    Once this has been done the re assembly can take place on brand new shafts.

    Once this is done cleaning through the oil hole to the cup and then a thorough clean of the arms itself is the final step in rocker arm preparation.

    Why not use new aftermarket rocker arms
    Quite simply because we saw too many issues with the ones available, either with pads breaking up or bad tolerances to the shaft meaning too much oil flow to the head and low oil pressure.










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    These bearings are your worst nightmare. Any sign of copper means you need to do something quick.

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    Often closer inspection will show hair line cracks, don't ignore them, as this is what you can expect.

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    [TH="colspan: 2, align: center"]If the rocker shafts are worn, it is a sure sign that the surface of the softer aluminium rockers is contaminated with particles from existing engine wear. Replacing the shafts without the rockers is worse than doing nothing.
    Why? Because new shafts will be eaten away by old rockers and create even more damaging metal particles to cause yet more engine damage.
    Not the best thing to have after an expensive
    and time-consuming engine rebuild.

    If they are worn, replace them all.
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  4. #4
    Join Date
    Jan 2010
    Location
    Melbourne
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    When John Eales build my 5.2, I asked the same question and was happy to pay for Alloy-roller arms. He advised to use the OEM cast ones and said he never seen a broken one despite some MG people rev them full during entire races. m

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