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Technical What is this white powder stuff?

Discussion in 'Traditional Hot Rods' started by Rodsports, Feb 15, 2020.

  1. Rodsports
    Joined: Sep 24, 2018
    Posts: 25


    G' day guys,

    Im hoping that someone can tell me what this white powder is. I pulled the heads (Ebelbrock aluminium) off my flathead today and some of the bolts have this white powder on them.

    When I put the heads back on should I coat the length of them with a light grease?

    Any advice would be appreciated.


    Flathead bolt.jpg
    rod1 likes this.
  2. redoxide
    Joined: Jul 7, 2002
    Posts: 602

    from Scotland

    I believe that some of the head bolts enter the water jackets. To prevent leaks bypassing the head bolts a sealant is applied to the threads . It may be the residue from the sealant . Although withdrawing the bolts would clear the threads so the other cause may be electrolysis a reaction between the steel bolt and the ali head, there would be corrosion damage to the head around the bolt holes if that were the case . If the bolts were reluctant to come out the head , the residue would catch in the threads as the bolts were pulled through..

    Given that the threads are clogged it might be the latter .. but looking closely the clogged threads are toward the top of the thread so there is a chance that is sealant residue that hasnt entered the tapped hole in the block ..

    What condition are the heads in around the bolt holes ?
    Last edited: Feb 15, 2020
  3. Rodsports
    Joined: Sep 24, 2018
    Posts: 25


    G'day Redoxide,

    They're fairly clean and the bolts came out easily. When I built the motor I used a thread sealer (a GM dealer product). The heads are clean as well.
    Your electrolysis theory makes sense, would a cause be from a poorly grounded block?
  4. redoxide
    Joined: Jul 7, 2002
    Posts: 602

    from Scotland

    You usually find that the head sacrifices some of its material in and around the area the dissimilar metals come into contact. If the heads are clean with no sign of electroysis damage, it might just be the sealant residue .. ?

    Im not any expert in this stuff , a wee bit research might answer the question of earthing. Its something to go on though.

  5. Torana68
    Joined: Jan 28, 2008
    Posts: 1,253

    from Australia

    What’s the hole that passes through look like cause that looks like alloy corrosion.
  6. demon452
    Joined: Dec 23, 2007
    Posts: 391

    from Michigan

    I use stuff called Indian head. It's a shellac gasket compound. I have been using it for years and never had a coolant leak around any bolt. But like everything else. Clean clean clean prior to applying
  7. It looks like liquid Teflon residue?
    I think GM head bolts are coated with a similar product .
    At least that is what a few sets of aftermarket GM head bolts I have purchased had on them .

    bchctybob likes this.
  8. flatout51
    Joined: Jul 26, 2006
    Posts: 1,019


    Some flathead head bolts pass into the water jackets. That's thread sealant. Get some permatex thread sealant before reinstalling them or you'll have a water leak.

    Sent from my SM-G977U using The H.A.M.B. mobile app
    Petejoe likes this.
  9. H380
    Joined: Sep 20, 2015
    Posts: 461

    from Louisiana

  10. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 26,632

    Jalopy Joker

    caused by aluminum reacting to dissimilar metal in water - common - to help prevent that need to run a sacrificial anode - some for use where normally drain petcock installs - some special radiator caps have anode attached - search on, etc
    Last edited: Feb 15, 2020
    kevinrevin and loudbang like this.
  11. Cocaine for a thousand Alex
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 48,679


    Aluminum oxide.
    bedwards, warbird1, BLACKNRED and 3 others like this.
  13. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    It's the stuff that kept that bolt from breaking off way down in the block!
  14. Not corrosion or galvanic. Galvanic would be between the alum head and what it touches, the block or bolt. Not the steel bolt in the cast iron block. It's thread sealant. Clean the bolts and use new sealant when putting back together.

    Sent from dumb operator on a smart phone
    Desoto291Hemi and bchctybob like this.
  15. AmishMike
    Joined: Mar 27, 2014
    Posts: 546


    ^^^ agreed. & run a tap down block holes
  16. oldolds
    Joined: Oct 18, 2010
    Posts: 3,153


    I was always told to not use a tap to chase threads. I was told it will cut new metal every time it goes in the hole. They make thread chasers that do not cut metal. They look similar to a bolt with a line cut straight down the bolt across the threads. At least that is what a machinist friend showed me.
    dirty old man and bchctybob like this.
  17. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,492


    Another vote for using a thread chaser instead of a tap.
  18. BJR
    Joined: Mar 11, 2005
    Posts: 6,898


    Kudos to the members of the Hamb. When I read the title asking about white powder, I was expecting this to go down hill fast. It didn't, guess I'm the only member with a warped mind.:eek:
  19. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 3,126

    Dick Stevens

    Thread chaser is the right thing to use, not a tap!
    warbird1 likes this.
    N2hotrods likes this.
  21. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    I took an extra bolt, used the Dremel to cut two vertical slots thru the threads opposite each other. Ran it up and down each hole a couple of times with acetone atf mix then used a brass spiral brush to clean up. Worked well.
  22. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,640


    Yes I was young and dumb when I did mine , all my studs seep because of it
    Desoto291Hemi likes this.
  23. Rodsports
    Joined: Sep 24, 2018
    Posts: 25


    Thanks guys, Ive been away with work for a few days so havent been able to respond. Back at it this weekend so will provide an update - really appreciate your help.

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