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Thread: Main cap walk

  1. #1
    396_WAYS_TO_SPIT
    when does it happen? What causes it? Does it happen with studs in a 2 bolt main? Does anyone offer main stud girdles for BBC?

  2. #2

  3. #3
    78Eliminator
    when does it happen? What causes it? Does it happen with studs in a 2 bolt main? Does anyone offer main stud girdles for BBC?
    Morg has a girdle in his sled. He is on alky and beats his motor pretty regularly and just had it apart to look at the mains. There was no evidence of any walking. Fiat48 had just balanced his rotating assembly and they also installed the girdle. Let Morg and Fiat tune in here and tell you what make the girdle is. I don't think studs in a 2 bolt or even a studded 4 bolt is going to stop anything from walking on a Gen IV block if it wants to walk. Lots of things cause cap walk from what I understand. Lots of horsepower and a bad rotating balance would do it.

  4. #4
    wsuwrhr
    You forgot incorrect torque and poor fasteners.
    But yea, what he said.
    Morg has a girdle in his sled. He is on alky and beats his motor pretty regularly and just had it apart to look at the mains. There was no evidence of any walking. Fiat48 had just balanced his rotating assembly and they also installed the girdle. Let Morg and Fiat tune in here and tell you what make the girdle is. I don't think studs in a 2 bolt or even a studded 4 bolt is going to stop anything from walking on a Gen IV block if it wants to walk. Lots of things cause cap walk from what I understand. Lots of horsepower and a bad rotating balance would do it.

  5. #5
    SmokinLowriderSS
    Stresses of that darned crankshaft trying to leave the engine cause it, and I don't think there is any real way to STOP it absolutely. Prevent it to a point, or minimize it, sure.
    Main stud girdles. I'm sure they exist for big Chevys, but:
    Summit only shows one for Ford mains.
    Jeggs doesn't show any.
    I KNOW they exist for Olds'.
    If they do exist somewheres, some of the racers and engine builders on here'll have a line on them.

  6. #6
    Senior Member
    Join Date
    Feb 2009
    Posts
    2,347
    We did put one of those girdles on my deal. Sort of an experiment.
    They need a bunch of work for clearance. I needed to grind for crank, oil pump drive, dipstick & oil pan clearance.
    My motor spins around 7500 to 7800 rpm when at a decent altitude. Pretty long runs.
    The mains showed no walk at all, zip, zero, nada.
    I would think the girdle helped. But I think the main reason is an absolutely straight line hone, correct clearances & a balanced rotating assembly.
    Now I have a few other things going for me. 3.76" stroke & injected alky. If this deal had a blower on top it may have been a different story. But my deal is just a used up 427 60 over with GM heads. Nothing special. Took it out of the family station wagon.
    The block is a 4 bolt.

  7. #7
    Senior Member
    Join Date
    Feb 2009
    Posts
    2,347
    Try here:
    http://cgi.ebay.com/ebaymotors/BILLE...tegoryZ33613QQ ssPageNameZWDVWQQrdZ1QQcmdZViewItem

  8. #8
    BrendellaJet
    How about the aftermarket blocks, mine has dowel pins to locate the main caps. Doesn't that help?

  9. #9
    Fiat48
    I suspect the dowel pins (Merlin) helps or stops the cap walk. But I built two of those and they never come back so I can look and see.
    However the Dart 541 (splayed cap, no studs...factory bolts) I built a few years back has just come home for a blower upgrade and the caps have not walked a bit. The whole motor looks excellent. I will reuse every bearing and even the rings.
    Remember 4 bolt splayed caps or dowel pins is not the whole story. Merlins and Darts have better oiling systems and the blocks are much stouter. And the crankshaft stiffness is a player.
    I was impressed enough by Morgs deal that I would use a girdle on any of the Chevrolet blocks. For those I think it is a must have in my opinion.

  10. #10
    Machinist
    Like was said above, if you have a good balance job, a straight line bore, and good fasteners, it's hard to walk the caps on a BBC. If any of the above are bad, the girdle is not going to help much.

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