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  • Engine Build Question......

    I am currently checking the specs on my 2.5L project.

    My main bearing oil clearances measured out at .0027", .0032", .0031", .0029", and .0029".

    For those of you who have built S-14s, isn't this a bit loose? From what I have been able to uncover, .0027" is supposed to be max.

    It leaves an interesting quandary. The way BMW sizes their bearings, you get a red dot crank and red dot bearings, and they are supposed to go together. As far as I know, no other sizes are available unless you go way oversize and have the crank ground. Since my crank, bearings, and block are all brand new, that seems like a ridiculous route to take.

    I was curious if there is some variation among "red dot" bearing shells, and if another set might spec out slightly different.

    I would greatly appreciate any input or suggestions, thanks.

  • #2
    Those aren't far off. Remember that each ten thousandth of an inch is 100 MILLIONTHS of an inch. You could have the shop play with the block and bearing caps to get things closer if you really have to. Some of that also depends on temperatures and measurement technique. Maybe email some of the S14 engine building gurus such as Checca, Fields, Stroes et al to get their POV too.

    Stan

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    • #3
      Thanks for the input Stan. Actually, I am the "shop". This is a DIY project.

      I may be obsessing too much about the slight excess clearance. I have read that .0025-.0035 is generally what most "racing" motors use. But, usually those stats are with regard to pushrod American V-8s. In the USA, most people regard those as the only high performance motors. I am not sure the specs are applicable to our S-14s.

      What is interesting to me, is that BMW doesn't really offer any way of adjusting the clearance. If you have a red dot crank, you use red dot bearings, and that is that. I imagine a lot of shops would have just relied on that, and assembled the engine without even measuring the actual clearance.

      On the other hand, bearing clearance is a critical measurement. The BMW specs I have uncovered dictate .0012" to .0027". That is what I am fretting a bit about.

      Any engine build gurus listening that can give me some perspective?

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      • #4
        You need to post this on the SIG. You would get an answer from all three of the Guru's, and many more I am sure.

        T

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        • #5
          Originally posted by Ironhead
          Thanks for the input Stan. Actually, I am the "shop". This is a DIY project.

          I may be obsessing too much about the slight excess clearance. I have read that .0025-.0035 is generally what most "racing" motors use. But, usually those stats are with regard to pushrod American V-8s. In the USA, most people regard those as the only high performance motors. I am not sure the specs are applicable to our S-14s.

          What is interesting to me, is that BMW doesn't really offer any way of adjusting the clearance. If you have a red dot crank, you use red dot bearings, and that is that. I imagine a lot of shops would have just relied on that, and assembled the engine without even measuring the actual clearance.

          On the other hand, bearing clearance is a critical measurement. The BMW specs I have uncovered dictate .0012" to .0027". That is what I am fretting a bit about.

          Any engine build gurus listening that can give me some perspective?
          I applaud the fact that you're taking this project on yourself. Reminds me of the couple who rebuilt their own S14 in their garage that was in the Roundel last year.

          88 M3 - LACHSSILBER/M TECH
          89 M3 - ALPINEWEISS II/SCHWARZ
          85 323I S52 - ALPINEWEISS/SCHWARZ
          91 M TECHNIC TURBO - MACAOBLAU/M TECH


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          • #6
            You need to post this on the SIG. You would get an answer from all three of the Guru's, and many more I am sure.
            Done, thanks for the advice.

            I applaud the fact that you're taking this project on yourself. Reminds me of the couple who rebuilt their own S14 in their garage that was in the Roundel last year.
            Did their engine grenade on startup?.....=b

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            • #7
              Here's some related material on what Gustave found with his aftermarket rod bearing clearances.

              Stan
              Last edited by Stan; 04-26-2003, 12:11 PM.

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              • #8
                i would also like to partake in some engine building here in teh next little while... maybe next summer... my gti 16 valve needs freshening, and altho its tempting to just do a valve job and some new rings, its also tempting to get stupid and throw the whole works at it. if that is the choice i make, and parts start showing up at the house by the dozen, then im going to need to learn a few things about it myself, as being a poor college student, paying somebody for labor just isn't gonna happen.

                :borg: <--- that looks more like terminator after he got his face banged off with that huge steel I beam...

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                • #9
                  The loosest you want to go is .0025. Generally between .0020 and .0025 is what you want them to be for the rod bearings AND main bearings on an S14.

                  318is 2litre

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