Main bearing clearance...how should I adjust?
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Main bearing clearance...how should I adjust?

  1. #1
    Super Moderator HammerDown's Avatar
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    Question Main bearing clearance...how should I adjust?

    Clevite P bearings in mains

    1) .0029

    2) .0025 (sand the back of the shell a smidgen) ?

    3) .0035 (x-bearing or run it)?

    4) .003 (run it)

    5) .0032 (x- bearing or run it)?


    Hopefully I'll be sizing my H rod bearings tomorrow > all rod/crank journals measure the same and rod big-ends are within .0002
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Hmm to be a full thousandth off from 1 bearing to the next is kind of alot. I think you are still within factory specs though. Is it the crankshaft that is off dimensionally?

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    Senior Member VAMI's Avatar
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    Is it to late for a line hone?Looks like the housing bores vary in size since the crank is within 2 tenths.

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    Senior Member VAMI's Avatar
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    a X bearing will give you .001 more.a ***-1 is tighter

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    Senior Member Morg's Avatar
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    Have you measured the saddles without the bearing?

    Are you getting consistent measurements??
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    No secrets Morgan.

  8. #7
    Super Moderator HammerDown's Avatar
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    Quote Originally Posted by VAMI View Post
    a X bearing will give you .001 more.a ***-1 is tighter
    I thought X bearings could come either way tighter/looser
    What's a *** ?
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

  9. #8
    Super Moderator HammerDown's Avatar
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    Quote Originally Posted by Morg View Post
    Have you measured the saddles without the bearing?

    Are you getting consistent measurements??
    Consistent before room temperature changes (morning vs afternoon) and when I measure in the same location.
    I just bore gauged the saddles again...I know I'm fighting a tenth or two as it's cooler in my basement, then it warms up mid day.

    No bearings in and zeroing the bore gauge on #1

    1) 0
    2) .0002 tight
    3) .0004-.0005 loose
    4) .0004 loose
    5) .0002 loose

    Think I'll just run what I have vs ordering two more sets of bearings to fight a few tenths either way.
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Senior Member VAMI's Avatar
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    for example 743 hx means hard brg with plus .001. 743-1 .001 less clearnace my *** just was the part number.

  11. #10
    I'm No Expert Shaun's Avatar
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    Quote Originally Posted by HammerDown View Post
    Consistent before room temperature changes (morning vs afternoon) and when I measure in the same location.
    I just bore gauged the saddles again...I know I'm fighting a tenth or two as it's cooler in my basement, then it warms up mid day.

    No bearings in and zeroing the bore gauge on #1

    1) 0
    2) .0002 tight
    3) .0004-.0005 loose
    4) .0004 loose
    5) .0002 loose

    Think I'll just run what I have vs ordering two more sets of bearings to fight a few tenths either way.
    No expert here but shouldnt this be done by setting the mic to specific measurment (in my case 2.9375) and zeroing the dial bore from that? Seams like going off #1 is a bad idea, what if #1 is out of spec? Now your basing the others off it.

  12. #11
    UMPBA.ORG sleekcrafter's Avatar
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    Did you check to see if the bores are round?
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  13. #12
    Super Moderator HammerDown's Avatar
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    Thumbs up

    Quote Originally Posted by Shaun View Post
    No expert here but shouldnt this be done by setting the mic to specific measurment (in my case 2.9375) and zeroing the dial bore from that? Seams like going off #1 is a bad idea, what if #1 is out of spec? Now your basing the others off it.
    Shaun, you're correct...I just did the "zeroing out" for a quick comparsion.

    HOWEVER...last night I set my mic at 2.9375/6 ( middle of the spec) and had at it. I belive acceptable run is between 2.9378 - 2.9373

    1) .0002 tight

    2).0004 tight

    3) this one's fuc*ed > measuring right of the oil hole it's .0002 loose >measuring left of the oil hole it's .0005 loose!

    4) .0002 loose

    5) .0001 loose

    Hopeing I could move #1-4 main bearings around, I then miced the thickness, nope..all exact!

    If I could bring #3 oil clearance down to .0028 - .003 I be happy.
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

  14. #13
    Super Moderator HammerDown's Avatar
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    Thumbs down

    Quote Originally Posted by sleekcrafter View Post
    Did you check to see if the bores are round?
    Perfect circles...no
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

  15. #14
    UMPBA.ORG sleekcrafter's Avatar
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    Quote Originally Posted by HammerDown View Post
    Shaun, you're correct...I just did the "zeroing out" for a quick comparsion.

    HOWEVER...last night I set my mic at 2.9375/6 ( middle of the spec) and had at it. I belive acceptable run is between 2.9378 - 2.9373

    1) .0002 tight

    2).0004 tight

    3) this one's fuc*ed > measuring right of the oil hole it's .0002 loose >measuring left of the oil hole it's .0005 loose!

    4) .0002 loose

    5) .0001 loose

    Hopeing I could move #1-4 main bearings around, I then miced the thickness, nope..all exact!

    If I could bring #3 oil clearance down to .0028 - .003 I be happy.
    Seeing you posted the torque spec your builder wanted, and the torque ARP lists, you gan go up in torque on that journal, and see what that nets you...
    Upper Midwest Power Boat Association
    DRAG BOAT RACING UMPBA #926


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