Crank snout deflection

Discussion in 'PSI Superchargers Tech Questions' started by Bjs344, May 23, 2020.

  1. Bjs344

    Bjs344 Member

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    im working on an external crank support for a new combo. This has a mandrel coming off the front of the blower pulley to spin a belt drive pump. The blower pulley is also a little farther from the front main than a BBC. I’m a little worried about the stiffness of the crank support so I added a diagonal link with an adjuster in it thinking I could maybe preload it a little in the opposite direction of the belt. I can’t pull a belt right yet but decided to see if I could measure any deflection at the end of the mandrel by preloading my adjusters. Too my amazement I can crank the mandrel down about .010”

    I guess I could just be measuring the crank moving around in the bearings magnified by the long snout and mandrel.

    Anybody ever measure crank deflection when pulling a belt tight? I run 8mm and pulled it pretty tight on the last combo to keep it from breaking the belt. Like <1/2” side to side cold which would get down to just about nothing when hot.
     
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  2. TOL

    TOL Active Member

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    Curious about a few things. Is your blower pulley back flange offset toward the crank hub plane? Are you truly measuring crank deflection or pulley deflection? .010" is a bunch. Why is your pulley out further then a normal BBC? Ever thought about doing a hub bearing support with a center flange pulley like an RCD hemi? Just an idea.......
     
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    Last edited: May 23, 2020
  3. Bjs344

    Bjs344 Member

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    I’m measuring deflection at the end of the mandrel. Mandrel sticks out through the crank support for a fuel pump pulley.

    Crank pulley is a standard rear flange (I guess that’s what you call it?) that is bolted to a harmonic balancer. So no way to move the belt backwards other than take the balancer off. I know, I know, blower motors don’t need a balancer..... but I made a decision and am oing to stick with it at this point until it flys or flops.

    Also, as far as I know, nobody had ever bolted a 14-71 to an LS so I just felt like I was in unknown territory and using the balancer was worth the extra snout length as long as I can support the end of it.
     
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  4. Bjs344

    Bjs344 Member

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    Also, I can get the deflection without much force (the adjusters crank pretty easy) and then it stops. So I must just be rocking the crank around in the bearings. Or squishing the front main a little:(
     
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