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Thread: Cylinder boring

  1. #1

    Default Cylinder boring

    I picked up an old Buma "AU" 2.2" to 4.2" range boring bar with mike and tools etc last week, sorted out the electricals and got it working, did some test bores with it, sofar so good, after a search on the web only found manuals for the "APM "and "JBM" at lathes uk

    This has a 1/4 HP motor what you expect for depth of cut?
    so far tried 0.010" and it seems to do that easly with a good bore finsh
    so for a +0.020 over bore, a 0.010 cut then 0.007 cut and leave 0.003" for the hone ? or strait to 0.017" cut and remaining 0.003 for the hone ? what do you guys think ?

    It has silversoldered carbide tooling and a diamond hone on the back of one of the pullys and jigs for the angles, how often to hone ? a quick touch up every bore ? or when the finish becomes bad ?

    if i wished to fit liners how much interferance would be required on the bore

    Similar to a Repco or Kwikway/ VanNorman

    looking here

    "http://bbs.homeshopmachinist.net/showthread.php?t=39959&highlight=cylinder+boring"

    its a similar machine with out the stand
    would the honing be done in the same stand ?

    any thing to watch out for when using it

    Any information would be appreciated

  2. #2
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    Default

    Just my opinion, but .003 seems like a lot to hone out. Why not shoot for .001 or .0015.

  3. #3
    Join Date
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    If you leave .001, what will you do if you have .002 taper? He's got it right. Make the first cut .010, see that you are straight and reasonably round, go close to size.
    While I agree that a cardinal rule of honing is to do as little as possible, .003 is nothing. 2-3 strokes with roughing stones and you'll be at .001-.0015. Change to finer stones and go for the finish.

  4. #4
    Join Date
    Sep 2009
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    NW Illinois USA
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    I have not used power honing equipment so can't comment on that.

    I use a Lisle rigid hone driven by a heavy duty drill motor on engine blocks bored with my old school Kwikway bar. I have good luck leaving .001 on the diameter for honing. Works for me.

    I also use a torque plate while honing. If your cylinder walls flex a lot with fastener loads you may want to either use the torque plate while boring as well or leave more material than .001.

    Not sure about liner intereference recommendation. I would shoot for about .001 on diameter for a 4 inch bore. Strongly suggest a step at the bottom of the bore for the liner to seat against.
    Last edited by strokersix; 06-07-2011 at 10:44 AM.

  5. #5
    Join Date
    Jan 2002
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    Western, Kentucky
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    When I did automotive machining we never left less than .003" in an engine cylinder for honing. If you leave any less than that, you don't remove all of the tool marks left by the boring tool. This leaves high peaks and deep valleys that will shorten the life of new piston rings. Of course, we used a rigid power hone to finish sizing the bores.

    I have heard that the old timers would bore an engine and not hone it or hone it very little and then run it for a while with a new set of sacrificial rings until the rings were worn out and the engine began smoking. It was then tore down and a second set of rings were installed on the now smooth cylinder. Don't know if this is true or not.
    "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

  6. #6

    Default

    Leaving .003" to hone is a long standing idea that was meant to insure removing all traces of tool marks from boring. It might have also been the suspect recommendation of the folks who sell honing stones! Anyhow, nice idea if you have room at the bottom of bore to overstroke enough to maintain straightness but it's a lot of work. Maybe some of the newer power honing equipment with shorter stones & automatic dwell (stopping at the bottom) does a better job but if you are using a Sunnen type hone in a drill or manually stroked honing cabinet and leave .003", on a Chevy 350 for instance, the main bearing webs prevent stroking through the bottom. You will end up with cylinders too tight at the bottom, or, if you get the bottom big enough the top will be too big.
    Long time users of quality Kwik-Way, Rottler, & Van Norman machines learn to sharpen & maintain bits to give the best finish possible, bore to within .0015" of finished size, a few strokes with medium grit brings you almost there, and finish up with the proper finishing stones for the rings you are using. Microscopic inspection might reveal some trace of tool marks under the cross hatch but lots of experience proves it's not an issue.
    Unless you are flooding with massive amounts of honing oil the heat generated with lots of honing causes cylinders to grow. Hone .003" to size with minimal coolant, check it next morning, and you will be undersize again. I'm with the folks who say leave less to hone. You'll end up with more consistent size bores, less taper, less work, and lower stone cost. If you are dealing with main web obstructions at the bottom be sure to rig a proper depth stop to avoid crashing and breaking stones, hones, & bones! Been there, done that!

  7. #7
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    Quote Originally Posted by johnd
    Anyhow, nice idea if you have room at the bottom of bore to overstroke enough to maintain straightness but it's a lot of work.
    When I would do 350 Chevys I either let the boring tool bore past the bottom of the cylinder to just above the main web or I would use a die grinder to grind that area away for stone clearance. Never had a problem keeping bores straight to less than 0.0005". Yes, I was using a Rottler honing machine and I did adjust the stone length depending on the length of the cylinder versus the diameter, but there is no reason it couldn't be done with a manual rigid hone and a drill motor.

    Many a 350 Chevy have been "bored" 0.030" over using only a Sunnen CK10 or a CV616 honing machine and nothing else. Not exactly the way I would want it done, but it works.

    One thing is for sure, you don't want to use the old spring loaded hones or flex hones to try to bring cylinders to size. They are just for breaking the glaze when doing a ring job.

    Quote Originally Posted by johnd
    Microscopic inspection might reveal some trace of tool marks under the cross hatch but lots of experience proves it's not an issue.
    I have to respectfully disagree with this one. The OEM's spend lots of time and money getting the cylinder finish right for engine longevity and oil consumption.
    Last edited by 3jaw; 06-07-2011 at 02:54 PM.
    "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

  8. #8
    Join Date
    Oct 2004
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    i have a buma

    no photos ..pics are gone

    http://bbs.homeshopmachinist.net/sho...highlight=buma

    all the best.markj

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