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Best way to ream to 0.944"?

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  • Best way to ream to 0.944"?

    I'm trying to rebuild an engine and I installed some new wrist pin bushings in my connecting rods. Only when I went to install the wrist pins did I find that the bushings are shipped deliberately undersized so they can be reamed to fit the wrist pins. Since I have a drill press and mini-lathe, I wondered if there was a way to do this myself.

    I can buy an 'H' sized hand-reamer, but the wrist pin bushings are split bushings, so each blade of a straight hand reamer might hang up in the split seam (there's not much of a split -- the two ends are pretty well wedged against each other -- but I can still feel a notch there with my finger). So rather than ream by hand, I wondered if I could use a hand reamer in a drill press or lathe spindle to keep that split seam from messing things up? Either under power, or just spinning the chuck or spindle by hand.

    Unless there is such a thing as a large spiral-flute adjustable reamer? I see a few of them on eBay but they are way too small for a hole nearly an inch wide.

    One thing that worries me is the tolerance of the final bushing ID is .0005" (half a thou), and I'm not sure that I, as a newbie, can hold this tight of a tolerance. My dial calipers are only accurate to .001", for example.

    Any suggestions? I accidentally ordered 4 sets of wrist pin bushings when I thought they were sold individually, so I can mess up quite a few of them before I give up and go to a real machine shop.

  • #2
    Don't power a hand reamer.....they are too aggresive for that......

    Split bushings can be reamed......how close can you get without me doing the math.......

    For first time attempt you may bellmouth the bushings by hand......

    How much under are they?

    Are they bronze?

    They make small hones for this in auto specialty tool stores if you are close to final size already......crude might even be a fine flap wheel or some emery in a slit rod and patience......how many rpm, what kind of engine?

    .0005 never changes but an antique stationary pump verses a 2 stroke dirt bike will be different applications.......grin
    Last edited by hardtail; 12-31-2010, 08:42 PM.
    Opportunity knocks once, temptation leans on the doorbell.....

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    • #3
      The old bushings were bronze-colored. The surface of the new ones is silver, but I see a layer of bronze underneath, where I drilled through for the oil holes.

      They are .020" undersize right now.

      Hm, a brake master cylinder hone might be about the right size. Not sure if .020" is considered "close" though.

      This is for a VW 1.6L turbo-diesel of about 100HP.

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      • #4
        Originally posted by tylernt
        The old bushings were bronze-colored. The surface of the new ones is silver, but I see a layer of bronze underneath, where I drilled through for the oil holes.

        They are .020" undersize right now.

        Hm, a brake master cylinder hone might be about the right size. Not sure if .020" is considered "close" though.

        This is for a VW 1.6L turbo-diesel of about 100HP.
        I wouldn't recommend the brake hone either......the hand reamer would probably be the better way to go.......the brake hone will probably bellmouth faster.......can you accurately measure the reamers settings and bore after?
        Opportunity knocks once, temptation leans on the doorbell.....

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        • #5
          Originally posted by hardtail
          can you accurately measure the reamers settings and bore after?
          Not really, my dial calipers are only accurate to .001". Can I just ream a bit at a time until the wrist pins just barely fit in the bushings?

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          • #6
            Check here: http://www.lavallee-ide.com/
            If need be, you can order a custom size, though the price might be a little high.
            ----------
            Try to make a living, not a killing. -- Utah Phillips
            Don't believe everything you know. -- Bumper sticker
            Everybody is ignorant, only on different subjects. -- Will Rogers
            There are lots of people who mistake their imagination for their memory. - Josh Billings
            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
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            • #7
              something like this ?:

              http://www.victornet.com/subdepartme...ml?id=T8diwShT

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              • #8
                Originally posted by RussZHC
                Hey that's it, a spiral flute adjustable hand reamer that goes up to the right size! $99 though... so now the question is, is a $36 straight flute reamer going to be "good enough" or is the spiral flute really needed for this split bushing?

                Pic:

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                • #9
                  I would suspect that you have more than one problem here.

                  Reaming to a tolerance like that with an adjustable reamer is in the realm of art, not science. You should get them all within .002-.005 before trying to hit a specific finish size. In other words if you sneak up to the proper adjustment on the first one, adjusting and measuring 4-10 times, and then think that the reamer is set to ream the other rods that still have .020 in them, the reamer will almost surely cut oversize.

                  The previous comment about bellmouth is right on. To that I would add squareness as a major concern. Without a jig to guide the reamer you have no way of knowing if the hole you just spent 15-45 minutes reaming to a nice push fit is anywhere near parallel to the bore in the big end of the rod.

                  Not wanting to throw cold water on your plans, just trying to help someone avoid some of the mistakes I have made.
                  Dave

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                  • #10
                    Spiral will work better.
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      Originally posted by becksmachine
                      The previous comment about bellmouth is right on. To that I would add squareness as a major concern. Without a jig to guide the reamer
                      Let's say I sweep a dial gauge in my drill press chuck on the machined face of the conrod big-end bore (same way you tram a mill). Assuming this machined face is square to the big-end bore, I can adjust my drill table to get the rod square to the quill. Now I just use my drill table to hold the small-end of the conrod, put light pressure on the quill, and turn the reamer by hand.

                      Workable?

                      Admittedly, this is a crummy Chinese DP but I hope the reamer is self-centering enough when turned by hand that a bit (well, actually, a lot) of runout in the DP is not going to hurt anything.

                      Not wanting to throw cold water on your plans, just trying to help someone avoid some of the mistakes I have made.
                      Much appreciated.

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                      • #12
                        This might be better done at an automotive engine rebuilder's shop. They are set up to do this job with all the tools and measuring equipment and can hone it out to a .0001 (and yes, rod end clearances are a matter of a few ten thousandths) with ease. You have to keep the rod bore exactly parallel to the crankshaft while you do it. Can you do that in your shop? Guaranteed? It's important...if the bore isn't parallel, the oil film is going to be compromised when the engine is running. One end of the bushing is going to have much tighter clearance on one half of the stroke and the other end will have the same problem on the other half of the stroke, and on the opposite side of the bushing. If it cuts through the oil film, you will be into metal to metal contact and all that implies.

                        I'm not saying this can't be done in a home shop environment, just that there is more to it than meets the eye.
                        Since this is in a VW 1.6L turbo-diesel engine, it stands to reason that it is something you want to have right the first time since it's a LOT of work to correct it if problems arise.
                        Location: Saskatoon, Saskatchewan, Canada

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                        • #13
                          I had a lousy time using an adjustable reamer. Never again. Grab, stick, go off centre, and that's after setting up a jig to keep it in line.

                          If you were worried about grabbing at the split line, the worry would be in case your bush turned, wouldn't it ? Can you make a small fitment to go into the oil hole you drilled and stay just below level. This would prevent the bush from turning, split or not.

                          Anyway, when you say .944" do you mean .9448 ? If so, then that's 24mm. Standard metric size.
                          Richard - SW London, UK, EU.

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                          • #14
                            Edited to remove wrong post.
                            Last edited by Arcane; 12-31-2010, 10:30 PM.
                            Location: Saskatoon, Saskatchewan, Canada

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                            • #15
                              Arcane has the right ideas. You cannot successfully ream those bushings with anything other than a special purpose fixed spiral reamer or a spiral fluted 'expansion' reamer (not an 'adjustable' reamer). They could be accurately sized with a Lisle Small Bore Hone or similar tool. These have controlled expansion, not spring loaded.

                              After sizing the holes the rods would need to be checked on an alignment fixture. All told, replacing pin bushings is not a simple job and you are well advised to take your rods to an automotive machine shop. They will likely use a Sunnen hone to size them. Even regular machine shops are often not well equipped to do this type of work.
                              Last edited by Don Young; 12-31-2010, 10:41 PM.
                              Don Young

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