Survey Rod and Main Oil Clearances

Discussion in 'PSI Superchargers Tech Questions' started by Mike Canter, Mar 9, 2005.

  1. Mike Canter

    Mike Canter Top Dragster
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    Given that it is a roots blower motor an aluminum block with aluminum rods with 60wt oil what are your thoughts and recommendations on rod and main oil clearances.
    The main jounals are 3" diameter and my rod journals are 2.374" diameter.

    I currently use .0035 on my rods and .004 on all the mains.
     
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    Mike Canter, Mar 9, 2005
  2. aj481x

    aj481x Member

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    I would agree, but not any more than that. You will find people who have success at .002 and at.005 and wouldn't consider changing. It probably isn't as critical as we think, and we know these bores aren't round at full load. IMO ;)
     
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    aj481x, Mar 9, 2005
  3. Mike Canter

    Mike Canter Top Dragster
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    Come on guys, anyone have any more data than that.
     
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    Mike Canter, Mar 10, 2005
  4. Ken Sitko

    Ken Sitko Super Comp

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    If you're talking about a hemi, I find that .0040 to .0045 on the mains is good, any more that and you might run into blackening issues when you push it hard. I wouldn't go less than .004 though.

    Brand new rods will usually start our pretty big, even up to .006", but the rods will collapse afer by about .002 only a few runs; I have measured some that only have .0025 clearance after a dozen runs. Some teams resize their rods after 8 or 10 runs to bring the clearance back to .004 or so.
     
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    Ken Sitko, Mar 10, 2005
  5. Ken Sitko

    Ken Sitko Super Comp

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    Sorry, a bit of bad grammar there.

    If you're talking about a hemi, I find that .0040 to .0045 on the mains is good, any more that and you might run into blackening issues when you push it hard. I wouldn't go less than .004 though.

    Brand new rods will usually start our pretty big, even up to .006", but the rods will collapse by about .002 after only a few runs; I have measured some that only have .0025 clearance after a dozen runs. Some teams resize their rods after 8 or 10 runs to bring the clearance back to .004 or so.
     
    #5
    Ken Sitko, Mar 10, 2005
  6. Mike Canter

    Mike Canter Top Dragster
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    Thanks Ken, the rod closing up would explain why Brad Anderson uses such a wide clearance off .006 to .008.

    This is what I have found out so far.

    Clevite states that for the correct oil clearances you first multiply the main or rod journal diameter by .001" and if high performance add .0005" to that answer. So if a 3.00" diameter journal that is 3 times .001 = .003" plus .0005 = .0035". Now that is for 30 wt to 50 wt oil in a non blown application. For 60 wt and 70 wt oil it appears that multipling the first answer by 1.5 vice adding .0005 brings it closer to what I found blown racers use. So for a 3.00 journal x .001" = .003 time 1.5 = .0045" and this always appears to be the prefered clearance bracketed by .004 to .005".

    Now Brian at GRP Rods told me that when our aluminum rods get heated to 200*F the journal may expand as much as .003" and the only thing holding the bearing in was the brass dowel and the oil pressure. Now ain't that scary. Now he did say to not try and compensate for that in the rod clearances. Brian did also state that the rods will close up some after a few runs.

    I then called Brad Anderson's shop and talked to the guys back in the block area and they said that their motors have a .0045 main bearing clearance and a .006 to .008" rod clearance. Again scary for me but if it closes up after a few runs then OK.

    It appears to me that the oil clearances are directly proportional to the journal diameter but only appears to be really critical for the mains and as long as you have a wide enough rod clearance and good oil pressure that the rods are just not as critical.

    So what do you think?????
     
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    Mike Canter, Mar 10, 2005

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