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Thread: Merlin 540 Main Bearing Clearance?

  1. #1
    Junior Member APPRENTICE
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    Aug 2004
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    Vancouver Island B.C.
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    Merlin 540 Main Bearing Clearance?

    Just going to assemble my motor, Checked main bearing clearance and I have .004 on the mains. I am using a dial bore gauge to messure. Very reputable machine shop did the machine work, Line bore, who specilizes in race engines and manufactures his own aluminum rods, tells me this is where he builds them, some as hi as .005? What do you think. He does build and dyno's many race engines in our area. When I dropped off my engine there were 3 other Merlin blocks sitting on the floor waiting in line.
    Thanks.
    1 OTHER NOTE! The main bores are supose to be no more than 2.938 and they are 2.940, Crank shaft is a little fat so I end up with .004 clearance. But don't I lose some of the crush on the bearing with the larger bore size?

  2. #2
    Senior Member RACING JUNKIE jmarksdragster's Avatar
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    Jul 2007
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    Florida
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    On everything I've read on the subject, if you get your rods around .0027 to .0033 you will be fine, mains .0033 to .0038 gets you in the ballpark. .004 mains won't hurt, but you can run a half set of .001 under to tighten up .0005, coated bearings will get about .0002 more if it concerns you. My SB2 ended up with .0028 rods and .0033 mains. Small or large journal sizes won't matter (or big block), you still need minimum clearances to get a proper wedge of oil. Check this post.
    http://speedtalk.com/forum/viewtopic...ring+clearance
    Mark Whitener
    http://racingfuelsystems.myfunforum.org
    __________

    Good work isn't cheap, and cheap work can't be good.

  3. #3
    Senior Member RACING JUNKIE
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    Quote Originally Posted by jmarksdragster
    On everything I've read on the subject, if you get your rods around .0027 to .0033 you will be fine, mains .0033 to .0038 gets you in the ballpark. .004 mains won't hurt, but you can run a half set of .001 under to tighten up .0005, coated bearings will get about .0002 more if it concerns you. My SB2 ended up with .0028 rods and .0033 mains. Small or large journal sizes won't matter (or big block), you still need minimum clearances to get a proper wedge of oil. Check this post.
    http://speedtalk.com/forum/viewtopic...ring+clearance
    Thanks Mark for bringing that post over, it's one of the most informative post i've seen in a long time, many shade tree mechanics have never heard of oval rod honing and the same people run too tight a clearance on their engines and wonder why they lose bearings.

    Zip.


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