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Technical My favor with the spark plug gods has run out.

Discussion in 'The Hokey Ass Message Board' started by gimpyshotrods, Aug 21, 2020.

  1. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
    ALLIANCE MEMBER

    I somehow managed to put together a high compression engine, and run it, with no issues, until now.

    Sunday was time for its first spark plug change, and this time, I was not so lucky. Several plugs were closed up nearly all the way, by making contact with the pistons.

    Do I need to break down and by a bulk pack of plugs, and keep swapping them until I get lucky, or, do conical seat 18mm spark plug indexing washers exist?

    My search says they either no longer exist, or never did.

    Do I adapt out to 14mm? That's a thing that I have seen done. The adapters are $6ea. They, alone, might be enough to fix this. My question then would be, what plug, at 14mm conical, is the equivalent of an Autolite 46?

    Anyone have any insights on this?
     
  2. swifty
    Joined: Dec 25, 2005
    Posts: 1,702

    swifty
    Member

    My son runs 2 washers under the plugs on his blown flathead due to the high-lift cam and the relationship of plug and valve, not due to a plug/piston thing. I'm not a flathead person so don't know if they are 18 or 14mm, I could check out one of his engines in my shed but someone else may be able to give you the answer before I make the trip over the yard. I do know that he will only use NGK plugs on all his engines.
     
    loudbang likes this.
  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
    ALLIANCE MEMBER

    It is the plug seat that is the problem. Mine are tapered, or conical, and would require a conical washer.

    Many 18mm plugs have flat washer seats. Those folks are lucky, as they only need a ground parallel flat washer, or two.
     
  4. 41rodderz
    Joined: Sep 27, 2010
    Posts: 5,194

    41rodderz
    Member
    from Oregon

    What engine ? Since the plugs are hitting you can try a shorter plug but if they are to far into the pocket your engine is not going to run great. I have known racers that were fanatical about indexing plugs but you are going to have to do some testing. Maybe google different plug makers to see what length they have on threads . Two things . Do other foreign makers use different plugs thread lengths then say U.S. / Canada. Now if you use an adaptor you could modify with work , to get the plug in far enough if you don’t hit it out of the gate. If your indexing your plugs with an adaptor you may get a few more gray hairs indexing the adaptors to.
     

  5. swifty
    Joined: Dec 25, 2005
    Posts: 1,702

    swifty
    Member

    Is it possible to find a shorter plug which is equivalent to the Autolite 46 and is suitable for your engine/application. You may have to buy just one 18/14 adapter and check out your plug, piston relationship. Do you have a spare head that you could use? If it works then $48 is a cheap fix. Here in Oz plugs alone are over $6 each. Best of luck.
     
  6. 41rodderz
    Joined: Sep 27, 2010
    Posts: 5,194

    41rodderz
    Member
    from Oregon

    Did you check with Jegs or Summit for indexing washers ?
     
  7. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
    ALLIANCE MEMBER

    Plugs are $2.79 USD here.
     
    loudbang likes this.
  8. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
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    Yup, 14mm, only.
     
  9. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
    ALLIANCE MEMBER

    It is a healthy Ford 200 inline 6.

    The current plugs have only 0.438" of threads. It is hard to imagine shorter than that. I don't need to index them, per se, I just need the elbow on the ground turned a little. The adapters have a hex on the top, so that makes the threads deeper. There are a whole lot more choices in 14mm plugs. I might stand a better chance in that arena, in terms of getting a good depth, and position.
     
  10. 41rodderz
    Joined: Sep 27, 2010
    Posts: 5,194

    41rodderz
    Member
    from Oregon

    I think your right if the plugs are the short ones . I like that you built a in liner. What type are your pistons ?
     
  11. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 715

    TrailerTrashToo
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    loudbang likes this.
  12. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
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  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
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    They are Silvolites.
     
  14. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 715

    TrailerTrashToo
    ALLIANCE MEMBER

    OOPS - Reading is fundamental...
     
    scotty t likes this.
  15. blowby
    Joined: Dec 27, 2012
    Posts: 6,858

    blowby
    Member
    from Nicasio Ca

    Might be out of luck on the washers. How about trimming into side electrode?
     
    loudbang likes this.
  16. How hard would it be to make some out of dead-soft copper sheet?
     
  17. BJR
    Joined: Mar 11, 2005
    Posts: 6,507

    BJR
    Member

    What about 18mm copper O rings?
     
  18. dalesnyder
    Joined: Feb 6, 2008
    Posts: 401

    dalesnyder
    Member

    Is it possible to trim the electrode and move the gap to the side .
     
    bchctybob, Black_Sheep and loudbang like this.
  19. I just looked up the Autolite 46 and noticed it’s a projected tip plug. Could you use a non projected tip plug?


    Sent from my iPhone using The H.A.M.B. mobile app
     
  20. v8flat44
    Joined: Nov 13, 2017
    Posts: 546

    v8flat44

  21. Moriarity
    Joined: Apr 11, 2001
    Posts: 19,155

    Moriarity
    SUPER MODERATOR
    Staff Member

    If you just need to turn the ground elbow some , how about putting the plugs in a lathe and machining the seat so the grounds turn out of the way, might take some trial and error, mark the outside of the plug with a sharpie, machine a little, reinstall and repeat.....
     
  22. squirrel
    Joined: Sep 23, 2004
    Posts: 46,847

    squirrel
    Member

  23. Paul
    Joined: Aug 29, 2002
    Posts: 15,024

    Paul
    Editor

    Last ditch effort, pull the head and carve a slight dimple in the pistons...
     
    lippy likes this.
  24. jebbesen
    Joined: Aug 18, 2015
    Posts: 461

    jebbesen
    Member
    from Winona, MN

  25. The elegant solution. . . If you can pull it off.
    ;)
     
    Truckdoctor Andy likes this.
  26. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,137

    Ebbsspeed
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    bchctybob likes this.
  27. jimmy six
    Joined: Mar 21, 2006
    Posts: 7,112

    jimmy six
    Member

    Check Mc Master and other sources for plain copper washers. I have used them as crush seals on tapered fittings and sealed leaks. This should be no different. I know extended tip give more power depending on the application but 90% of the 50’s engines did not use them. In my racing since I have custom pistons made to get very high compression I too must make sure plugs are not hitting.
    I’m sure there are available copper washers in different thickness to help with this problem. Spark plugs will work with 3/8” of thread.. SBC’s were originally that way and so were the stove bolt 6’s. Cast iron head is very forgiving...Good luck.
     
  28. King ford
    Joined: Mar 18, 2013
    Posts: 1,380

    King ford
    ALLIANCE MEMBER
    from 08302

    Often a spark plug that indexes to between 10 and 2 o’clock in one hole will be incorrect in another hole. It’s standard fare in north east big block modified racing circles to buy 2 boxes of plugs, put a sharpie mark on the outside indicating the ground electrode and swap them around until you get everyone happy!
     
  29. lippy
    Joined: Sep 27, 2006
    Posts: 4,962

    lippy
    Member
    from Ks

    Do you have a domed piston? Lippy
     
  30. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,630

    gimpyshotrods
    ALLIANCE MEMBER

    I'll try that first, since I accidentally proved it works, with the first set of plugs.
     
    bchctybob and TrailerTrashToo like this.

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