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Zinc oil additive

Discussion in 'Norton Commando Motorcycles (Classic)' started by Foxy, Nov 26, 2010.

  1. MexicoMike


    Jan 31, 2010
    Assuming I'm seeing that pic correctly, that the 3rd lobe from the left is worn down, leaving a peak on the left side of the lobe:

    Frankly that looks like one of three things: Improper cam break-in OR lifters were removed and not replaced in the same position OR old lifters were re-used with a replacement cam. Of course, a defective new lifter or defective new cam could cause it as well.

    Improper cam break-in can ruin a new cam in 1000 miles but you don't usually see ONE bad lobe. However, putting used lifters back in a different location will grind down a cam quite rapidly. What is shown in the pic is typical of that sort of wear.

    Lifters have a convex surface when new. When they wear against the cam, the lifter surface can become concave. If that concave lifter stays where it was with the same cam it will work fine with no issues at all because the cam/lifter have worn-in together. But if the concave lifter is placed in a different position, it can quickly grind the lobe away. If a lifter is still convex and put in a different position, it MIGHT be fine; it might not. The "rule" is you ONLY re-use lifters if they are going back with the same cam they were with and in the same location. Frankly, NEVER re-using lifters is a safer rule! ;)

    If none of those things occurred with that engine, it may be a lack of oil (somehow - not sure how that would occur) to that one lobe/lifter. Since it only appears to affect one lobe, the choice of oil/additives is unlikely to be relevant. The only other thing that occurs to me re that wear is excessive valve spring pressure. But the only way that could occur is if someone put the wrong spring under that valve or if the coil was binding. Though if someone installed heavier springs and the cam wasn't as hard as it should be, that could happen.
    Last edited: Aug 21, 2018
  2. Deets55

    Deets55 VIP MEMBER

    Oct 3, 2013
    Same thing on mine, just different lobe. 30k on Speedo and upon disassembly engine appeared to have never been taken apart before. Large end bearings did not show excessive wear.
  3. maylar

    maylar VIP MEMBER

    May 13, 2007
    Engine had never been apart beyond a cylinder bore and valve guide replacement - I'm the original owner. The bike had one cylinder running poorly (duh) and some oil consumption, which led me to the teardown. Other than guides and pistons the engine was as delivered by the factory at that point. It's possible though not likely that I swapped lifters years ago, but I'm pretty anal about such things so I doubt it.
  4. MexicoMike


    Jan 31, 2010
    Interesting! Absent the issues that I posted in my earlier post, the only thing I could suggest is an improperly hardened cam. That does happen on occasion, even from well known cam suppliers. As I said, improper oil would have the same effect on all the lobes/rotating surfaces; it wouldn't single out one lobe.
    marinatlas likes this.
  5. Biscuit


    Sep 10, 2012
    At the shop I once worked at, we found 3 MK3s with knife edged cams like these last two pictures. It's pretty well documented that the MK3s did suffer from unevenly hardened cams, apparently some MK2s as well. I'd say more than likely these two examples suffered from "the soft cam syndrome" and not poor quality oil or improper engine work. My own MK3 needed to it's cam replaced too. It was always serviced with Castrol GTX 20w50 but at 38,000 miles or so, one exhaust rocker was needing adjustment quite frequently, always just a .002-003" too wide. Also a bit of fuzz was showing up on the magnetic drain plug. It still ran well, but I suspected the cam was on the way out and a teardown showed the beginnings of a bad lobe. The extra clearance, of course, was the result of accelerated wear on that lobes follower as the two parts could not get along anymore. - Pete

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