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Thread: Which model piston

  1. #1

    Which model piston

    Does anyone have a good idea of which BMW motor this piston came out of? I was told it might be out of a R69s but I think
    the five rings say otherwise. Itís a 72+ mm Nural. Thanks, Michael
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  2. #2
    Liaison 20774's Avatar
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    Well, they don't look like the late 60s piston (3-ring) that came out of my R69S. Those are some really scooped out spots for the valves. My R69S had more flat sections in that area. I'm not sure what high performance engine from the 1960s those would have come out of. A 5-ring setup seems old school...I thought they had pretty much gotten away from that later in the 1960s. Here's pictures of my R69S pistons.
    PistonLetteringx.jpgWristPinEndx.jpg
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Quote Originally Posted by 20774 View Post
    Well, they don't look like the late 60s piston (3-ring) that came out of my R69S. Those are some really scooped out spots for the valves. My R69S had more flat sections in that area. I'm not sure what high performance engine from the 1960s those would have come out of. A 5-ring setup seems old school...I thought they had pretty much gotten away from that later in the 1960s. Here's pictures of my R69S pistons.
    PistonLetteringx.jpgWristPinEndx.jpg
    Yes, the piston is domed with no flat spot and the 5 rings seem to make it pre 1960. I was hoping somebody would know what a original R69 (not S) piston would look like. I got the piston from Blue Moon
    for a display I have and I think they just had it sitting around for years.

  4. #4
    Liaison 20774's Avatar
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    I'm sure Vech at Bench Mark Works woud know. Let us know what you find out.

    Added thought...the R67 series in the early to mid 1950s also had 72mm pistons. Not high compression but maybe the pockets were needed to accommodate the valve train at the time.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
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    Reminds me of some of the old Alpha-Romeo pistons from many years back.
    Dave Hutton '78 R100S (mfg 7/77)

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