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Technical SBC Distributor Cam Gear Noise

Discussion in 'Traditional Hot Rods' started by 73SD, Dec 19, 2017.

  1. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Just replaced the factory dizzy on a 1990 5.7 (non roller cam) with a Summit house brand billet unit. It's making a heck of a whining noise now. I've taken measurements between both units and they are pretty much spot on with each other. The only thing I can see different is the "top land' area of the new dizzy gear is a little more narrow. Also, the I.D. of both gears are .491".

    Any ideas?
     
  2. Deuces
    Joined: Nov 3, 2009
    Posts: 18,476

    Deuces
    Member
    from Michigan

    What kind of metal is the old stock gear made of???
     
  3. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    That's a good question. I hate to say I "assume" it's melonized. The dizzy I ordered was supposedly a factory replacement for this model engine. The dizzy gear on the new one's specs is melonized.

    Ive read several contradicting articles on cam material in the mid 80s to mid 90s. Some state melonized gears were common even as far back as 85. This is my question, Should the dizzy gear be iron instead of melonized even though mine is a roller block that came factory with a non roller cam?
     
  4. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Here are the two for comparison -
     

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  5. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,507

    dirty old man
    ALLIANCE MEMBER

    One thing that can happen when changing distributors on SBC is that the replacement could be longer than the original, enough to bottom out on the oil pump shaft and push down enough to bind up the gear on pump shaft inside pump to bottom out and press on the bottom plate of the pump.
    This is why some of the replacement hipo distributors have a top collar that is movable vertically and locked in place with a set screw.
    A close comparison of the length from bottom of collar to botrtom of dist. gear may give you some insight on this.
    Also, if you have run it enough for the cam gear to shine up the gear on dist. a comparison of location of the shined area on a vertical plane between the 2 dist. gears may offer some clue.
    You say that the cam is non roller, but the block is OEM for roller. If you bought dist. specifying '90 engine, you may well have a dist. with gear for roller cam. Who knows? The manufacturer is most likely in China if it's Summit brand, so that may be a problem.:eek:
     
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  6. Terrible80
    Joined: Oct 1, 2010
    Posts: 748

    Terrible80
    ALLIANCE MEMBER

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  7. TagMan
    Joined: Dec 12, 2002
    Posts: 6,009

    TagMan
    ALLIANCE MEMBER

    On a helical gear, which is what the distributor gear is, the contact area of the gear tooth is dependant on the hob (cutter) used to form the tooth, as well as machine settings. The final tooth form must match the gear tooth on the cam, if not, there could well be noise. I'd pull the distributor and use gear tooth marking compound, reinsert the dist, and turn the engine by hand while putting light pressure on the rotor shaft. Then pull the distributor and check the gear tooth pattern. You might want to check it against the older unit and see how it compares.
     
  8. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
    Member
    from Central Ca

    Terrible80 likes this.
  9. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Yea, your last quote could very well be correct.
    Both distributors measure within just a few thousandths of each other with one exception. The oil pump drive blade inside the dizzy gear extends down about .0265" farther than the factory one. Here's my concern now, if my cam needs an iron dizzy gear and this one is melonized how much damage has or may have been caused by running it about 20 minutes? There are no shiny wear marks on the new dizzy gear but I looked at the cam gear with a bore scope and see some really shiny marks on it.
     
  10. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,247

    2OLD2FAST
    Member
    from illinois

    Why not just swap gears ??
     
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  11. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Well that's kind of what I'm leaning towards. My only concern is any damage the new gear could have already caused to the cam gear.
     
  12. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,247

    2OLD2FAST
    Member
    from illinois

    In all likelyhood , you haven't damaged the cam ...
     
  13. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,507

    dirty old man
    ALLIANCE MEMBER

    The distance between the bottom surface of the stop collar machined onto dist housing to the bottom of the dist gear on the 2 different dist. is what is critical on the possibility I'm talking about. If you get some sort of oil soluble marking compound to as suggested by Tagman, you can at least tell where the 2 gears are meshing.
     
  14. BJR
    Joined: Mar 11, 2005
    Posts: 6,295

    BJR
    Member

    ddn072211adcomedyGa_981059a.jpg
     
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  15. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

  16. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,507

    dirty old man
    ALLIANCE MEMBER

    After reviewing my last post, I'll add that the distance that the pump drive cross bar is recessed into the bottom of the gear needs to be factored into the equation when comparing length difference between the 2 distributors protrusion into the engine.
    Been 2 days since your last post 73SD, anything further to report?
     
    ottoman likes this.
  17. put 2 or 3 gaskets under it and see if it's better.
     
  18. jimvette59
    Joined: Apr 28, 2008
    Posts: 772

    jimvette59
    Member

    That Summit gear is wrong it has the wrong pitch. Call them and let them know . JMHO
     
    Last edited: Dec 21, 2017
  19. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Been out of town for the last few days. Going to the shop this afternoon and will give an update this evening. And yes, the drive tang recessed into the gear is .0265" longer than the stock one so that's what I'll check first.
     
  20. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    It definitely appears to vary somewhat from the original. I know the "top land" of the new gear is more narrow for sure. As far as the pitch being different, I was under the impression there is only one standard pitch on all sbc drive gears. I could very well be wrong though. I called Summit and spoke with tech. They just said it sounds like a bad distributor; send it back and we'll give you another. Not much of an answer in my opinion.
     
  21. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Yes, if the gear drive tang turns out to be too long I'll add the difference in a thick gasket/shim to accommodate the difference.
     
  22. Gr8laker
    Joined: Sep 15, 2011
    Posts: 58

    Gr8laker
    Member
    from Michigan

    Is the degree of helix on the gear teeth the same between the two distributors?

    Sent from my SM-T377V using The H.A.M.B. mobile app
     
  23. jimvette59
    Joined: Apr 28, 2008
    Posts: 772

    jimvette59
    Member

    Don" get to deep into the design of the gear . It is the wrong gear send it back . Old machinist. JMHO
     
  24. scrappybunch
    Joined: Nov 16, 2011
    Posts: 306

    scrappybunch
    Member
    from nj

    If you move the housing up with shims, keep an eye on the oil passage groove. It supply's oil to the r/s lifter galley. Honestly don't understand why your messing with it, send it back try another brand.
     
  25. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    It "appears" to be. The two will mesh with one another.
     
  26. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    I'm not arguing that. It's definitely different than the old one. Just for comparison I ordered another gear from a local parts house and it looks exactly like the one on the summit distributor. It doesn't make since. I know the distributor is factory stock and is the correct one for the motor. I'm thinking these replacement gears are for roller cams and not a flat tappet as used in the pickup engines.
     
  27. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    With the distributor installed and clamped down I can move the distributor shaft up and down so I would't think the whining is coming from the shaft being in a bind with the oil pump.
     
  28. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    The reason I was trying to make this one work was because I needed to get my truck back on the road as soon as possible. The other oem type distributors summit offered at the time had an estimated ship time of mid January before shipping. If I could find a NOS GM unit I'd buy it and be done with it.
     
  29. 73SD
    Joined: May 29, 2017
    Posts: 32

    73SD

    Just an update. Ordered a different brand distributor and installed. I still have the same issue. I've installed dozens of distributors in sbc engines and never ever ran across this before. Took all measurements on this one and everything is in spec. The gears looks almost identical to the factory unit. The spec on the gear is iron. Only thing left to try is find a factory GM unit and install and see what happens. If it does the same thing I figure the cam gear has been damaged by the first unit installed.
     

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