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20 thow pistons

Discussion in '"Stock" Alpine' started by bobbo, May 8, 2021.

  1. bobbo

    bobbo Gold Level Sponsor

    Just pulled the oversize pistons ( 20 thow. ) from my 1725. Notice they have a 4th groove just above the lower end of the piston skirt. Not an issue as I checked the rings I got from Classic Sunbeam, 4 rings supplied.
    Just wondering why the 4th groove? Looks like a second oil ring.
    Enquiring minds need to know.
  2. junkman

    junkman Gold Level Sponsor

    Couple of different trains of thought on the 4 ring deal. Some say over kill, not needed, others think they are necessary. The only time I used them I left the lower ring out as per advise from the the seller and had no issues. Far as I know the engine is still going.
  3. sunalp

    sunalp Platinum Level Sponsor

    I've used the 4 ring pistons a few times and , on advice from my machinist and a very knowledgeable
    friend, left the fourth ring off. Never an issue as they're not needed for this application.
    Not sure what application they'd be needed.
  4. bobbo

    bobbo Gold Level Sponsor

    Not much info on Google as to 4 groove pistons, or the reasons for a second oil ring, which is what I have on these 20 thow over pistons. Mostly chatter about extra drag from the 4th ring, loss of horse power etc. seems they were common in Ford flat-heads and diesel set-ups. Some indication they were needed to reduce oil consumption on mirror finished cylinders and not needed on cross hatched honed. Most say, just leave the secondary oil ring out. It would be nice if anyone has a clear direction for this. Not sure which way to go on this one.
  5. Filister

    Filister Silver Level Sponsor

    As I recall, the 4th ring was an oil control ring for high mileage engines in areas where proper machinery was not available for a proper overbore.

    I have left them off with no problem.
  6. bobbo

    bobbo Gold Level Sponsor

    Train of thought is " forgettaboutit" not required. So any one want a set of 4th groove rings? ( may-bee I'll post them on Free to a good home )
    Ill be leaving them out.
    Thanks all for your info.

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