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  •  » Indexing Bellhousing

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    12/23/2018 8:41 PM  #1

    Chaplin
    Senior 24-7 FYI Addict

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    Registered: 3/14/2015
    Posts: 1,027

    Indexing Bellhousing

    Ok, I need a little help here.  I understand the process of indexing the bell, but after watching a bunch of videos and trying to make my dial indicator work, it doesn’t make sense that the results people are getting are accurate.

    If I stick the magnetic base for the dial indicator on the flywheel, it seems to me that in order to get accurate readings, the base of the dial indicator would need to be dead center of the crank centerline, but it doesn’t look like anyone gives any consideration to getting the base of the dial indicator centered. For example, if you pushed the base of the dial indicator as far as you could in one direction, wouldn’t that cause the measured run out to be significantly greater 180 degrees from the magnet base than it actually would be if the magnet base were dead center in the crank centerline? 

    I figured I’d check the runout on my stock T-5 bell, but I am beginning to regret ever starting down this path!

     

    12/23/2018 9:49 PM  #2

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,300

    Re: Indexing Bellhousing

    Figure it like this.  If you have a fixed point mounted to the flywheel, 2” off center, and that point rotates about the centerline of the crank, it will form a perfect 4” diameter circle.
    The dial indicator base equates to that fixed point. The indicator’s measurement pin will then measure how far the hole in the bellhousing is from that 4” circle.

    You are not trying to measure the diameter of the hole. You are trying to determine how far off center the hole is.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    12/23/2018 10:27 PM  #3

    Bentworker
    I FYI 24-7

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    Registered: 9/17/2017
    Posts: 475

    Re: Indexing Bellhousing

    You'll get that "AH HA" moment soon.

    No guarantee that what I am typing will bring that moment to you any sooner (maybe later).

    1) Pull the spark plugs.
    2) Get out your favorite ratchet or breaker bar to turn the crank over.
    3) Break out the magnetic base, arm and dial indicator.
    4) Carefully apply that base anywhere you see fit (that is flat) on that flywheel.
    5) Adjust the arm and indicator so that the tip is riding on a good machined surface in the center bore of the bell housing, with it oriented so you can read it and the geometry correct so what you read on the dial is actually what is going on in reality.
    6) Carefully sweep the indicator 360 degrees (by turning the crankshaft), taking readings every 90 degrees.
    7) Use offset dowel pins if needed to correct error.
    8) Measure again to check correction.

    Why the location of the base does not matter is this.  No matter where you slap that base on the flywheel the center of the radius is always going to be the center of the crankshaft as you turn the crankshaft.  Most of the error is going to come from improper indicator geometry.

    Make sure you have your indicator set up correctly.  If not calamity can ensue.  Nothing catastrophic, but if not set up as designed you can get some readings that are way off.  Good news is that the geometry won't change much as you sweep 360, so even though your reads might be off, they will all be off by the same factor.  So your reads might indicate you need to move the bell housing .020" to the right, but because you had the indicator stylus arm set up at a 45 degree angle to the work instead of 90* the bell housing might only be .014" to the right.  So you go out and buy some offset pins to move it .020" and then measure your hard work and now realize you are now .004" to the left.



    Clear as mud?
     

     

    12/24/2018 6:50 AM  #4

    TKOPerformance
    Hyper FYIFORD ADDICT

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    From: Newark, DE
    Registered: 12/15/2014
    Posts: 7,526

    Re: Indexing Bellhousing

    Its worth noting that I've never seen a factory bellhousing that required correction.  The only time this has ever been an issue for me was working with aftermarket scattershields.  What we found was that at high RPM at the end of the track (1/4 mile) the trans could not be pulled into 4th gear.  In 4th you are directly coupling the input and output shafts, and when those two shaft centerlines are not aligned the slider simply won't engage the input shaft. 

    BUT, like I said, with a factory bellhousing the tolerances always seemed to be well within spec.  I think the difference is a cast and machined part vs. a hydroformed or stamped part in terms of how tight the tolerances can be in production. 

     

    12/24/2018 11:08 AM  #5

    Chaplin
    Senior 24-7 FYI Addict

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    Registered: 3/14/2015
    Posts: 1,027

    Re: Indexing Bellhousing

    Thanks guys. That makes sense and I understand it conceptually but was having a hard time visualizing it in my mind.

    I used a different magnetic base and dial indicator this morning and was able to get repeatable results and everywhere I measured was within .003 of zero, so that’s fine.

    TKO- The only reason I decided to check the factory bell is because of the aftermarket block- wasn’t sure if there’d be a variance with it from a factory casting. Apparently there isn’t! 

    If I get some more time this afternoon, I’ll throw on the clutch and pressure plate and bolt up to the trans and get it ready to drop in the car some point later this week.

    Last edited by Chaplin (12/24/2018 11:08 AM)

       •Thread Starter
     

    12/24/2018 1:14 PM  #6

    TKOPerformance
    Hyper FYIFORD ADDICT

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    From: Newark, DE
    Registered: 12/15/2014
    Posts: 7,526

    Re: Indexing Bellhousing

    Understandable.  Anytime you are using nonstock parts its a good idea to check it.  The last couple engine builds I've done the machine shop file fit the rings for me.  I still checked each top and second ring prior to installation.  I never found an issue, but I know what happens if you don't check.  Years ago a guy I work with rebuilt a 454 for his boat.  He was out in the shop bolting it together and I asked him how the bearing clearances looked.  He looked at me cockeyed as if to say "what do you mean?"  So I said "you checked them with plastigauge at least, right?"  He said "it all just came back from the machine shop; it's fine".  Well, it wasn't fine.  Somehow he got a set of standard bearings and a crank that was cut 0.010" undersize.  This wasn't discovered until the engine was back in the boat and test run.  To say it lived a short and unhappy life would be a bit of an understatement.  During the second assembly I watched him using a micrometer and dial dial bore gauge to check the clearances.  Overkill IMO, as plastigauge would have shown him if he had a problem, but I suppose the bill he had from the first go round made him gun shy.  When should a 45 year old man listen to a 20 year old kid?  When the 20 year old kid's built more engines than he has

     

    12/24/2018 9:50 PM  #7

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,300

    Re: Indexing Bellhousing

    Set the gauge up so the measuring tip of the gauge points from the crank center outward to the point where you take your reading. That way, the dimension on the gauge is the actual dimension.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

     

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