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Thread: Crank bearings

  1. #1

    Default Crank bearings

    Got a new project car 86 gt with a 302. Opened the motor to check it out and I noticed the main thrust crank bearing has .010 on it. But none of the others do. I was told the motor was never opened up before. Is this a normal thing from the factory. Name:  971D1E65-6FF4-45A8-98D6-D7B4613CABC8.jpg
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  2. #2

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    If I had to guess, ".010 U.S." means 0.010" under-size, a non-never-opened-up-before replacement bearing. If never opened up before (lol... why does everybody tell us whatever BS comes into their mind that they have no clue about, to sell things? Nevermind, answered my own question, lol... or there was some sort of mishap at the factory and the middle thrust main journal was required to be ground "10-under"... which sucks for the next guy, needing to buy two sets of bearings... who knows), all of the main journals should measure 2.2482-2.2490", and all of the rod journals should measure 2.1228-2.1236". A "10-under mains/rods" crank will have main journals at 2.2382-2.2390", and rod journals at 2.1128-2.1136". Better measure all of the journal diameters prior to getting new bearings.
    Last edited by Walking-Tall; 08-07-2018 at 04:15 PM.
    Mike
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  3. #3

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    Ill measure them and let you know what they are. I got part numbers of the thrust bearing and the other 4 mains. Idk if that will help determine if just the middle is .010 under or all of them. Thanks

  4. #4

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    This was a super quick measurement to give you an idea but cranks 1-5 were 2.247 2.245 2.247 2.247 2.249 and Rods were 2.120 and one was 2.121

  5. #5
    FEP Supporter BMW Rider's Avatar
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    My guess would be the thrust faces are the oversize.

  6. #6

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    There ford factory bearings by the looks of it but I’m not sure. If the thrust is oversized than the rest have to be also because the tolerances are so close together. As for the rods they don’t match what walking tall list so I’m not sure if those are original or not. But they are stamped ford with a long part number like the mains.

  7. #7
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    That is a ford bearing , and the date is June 83 .
    clowns to the left of me , Jokers to the right

  8. #8

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    Quote Originally Posted by BMW Rider View Post
    My guess would be the thrust faces are the oversize.
    This would be my guess as well. Notice BMW Rider said thrust faces are oversize. This is independent of the shaft size portion of the bearing. It means the flange portion of the bearing perpinducular to the journal is .010" thicker than a std bearing would be at the flange. If you will measure your thrust bearing from outside flange to outside flange I can confirm this for you. Bearings with oversize thrust are available, just not nearly as common. So, don't panic it's solvable.

    If you are accurately measuring your rod journals, then they are under spec. However, if they are not out of round and have acceptable taper, then with .001 undersize bearings, your clearances may still work out especially if the housing bore of your connecting rods is on the tight side.
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  9. #9

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    I’ll measure that for you when I get home tonight. So you want the thrust face to the other thrust face dimensions. And I measured them with digital calipers the best I could. Here’s a pic of the one rod bearing factory markings. Name:  66F8C6CA-3C93-4373-B245-F15610A09DE4.jpg
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  10. #10
    FEP Power Member Ourobos's Avatar
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    Those are with a micrometer or a caliper?
    1986 CHP SSP Coupe

  11. #11

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    Caliper that I had lying around in the garage. Going to mic them later tonight. Just did it quick running out the door.

  12. #12

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    Quote Originally Posted by 80Merccapri View Post
    Iíll measure that for you when I get home tonight. So you want the thrust face to the other thrust face dimensions. And I measured them with digital calipers the best I could. Hereís a pic of the one rod bearing factory markings. Name:  66F8C6CA-3C93-4373-B245-F15610A09DE4.jpg
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    Calipers are ok for the thrust face to thrust face dimension I requested.

    For crankshaft journals, they need to be measured with a micrometer, preferably of good brand like Starrett or Mititoyo. Micrometer also must read in .0001" increments to detect taper and out of round. Not to discourage you, but measuring round journals with a mic takes a bit of practice to get good repeatable results. I would really recommend someone with experience do this for you or at least show you how it's done.
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  13. #13

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    Alright I’ll get those to you later tonight. And thanks for the heads up my dads been a machinist for over 30 years so I’ll have him help me out to make sure it accurate. I’ll report back once I get those measurements. thanks everyone

  14. #14
    FEP Super Member gr79's Avatar
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    While in engine plants, have walked past running production crank depts at Ford and GM.
    Errors happen. Dept runs 24/7. Lots of machinery.
    They wont scrap a crank or block because of an error than can be corrected.
    Crank or block fails inspection, tag and set it aside for rework, reclaim it later.
    Crank journal may have got nicked in process handling or something.
    Other internal engine parts are select fit too.

  15. #15

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    Thrust bearing measures 1.130

  16. #16

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    Quote Originally Posted by 80Merccapri View Post
    Thrust bearing measures 1.130
    Well, that is the correct width of a standard thickness thrust bearing. A .010 over thrust should measure about 1.143.
    I'm not sure why your thrust bearing is marked that way... It could have gotten mismarked when manufactured. I have personally seen a bearing marked .010 that was actually .020.....

    The good news being that it looks like a regular old standard replacement bearing set should work. Well as previously mentioned, as long as the journals are not out of round, have acceptable taper, and the finish is acceptable. Since you have someone to help you measure, I'll go ahead and give you the specs to look for. Out of round should not exceed .0001" and Taper (front to back) should not exceed .0004, although I like to see no more than .0002 for a performance application. Feel free to ask me any questions and I'll do my best to help.
    '79 Fairmont Futura
    '79 Mercury Zephyr wagon
    '83 LTD Wagon - future Mustang "Sport" Wagon
    '84 Mercury Capri RS - 5.0 5spd
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  17. #17

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    I appreciate all the help. With all the journals being similar size even with a caliper they are most likely the same size and the thrust bearing wasn’t Put in because of a nicked journal that needed machined. I’m going to get them measured with a mic here and know for sure. But it seems like a std bearing set might be it.

  18. #18

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    I agree the next step is to mic that thrust journal. If it is the correct diameter for a standard journal (2.2482-2.2490) then the thrust bearing shell must have been mismarked by accident.
    '79 Fairmont Futura
    '79 Mercury Zephyr wagon
    '83 LTD Wagon - future Mustang "Sport" Wagon
    '84 Mercury Capri RS - 5.0 5spd
    Owner of Victory Engines and Machining, LLC
    g2G

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