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Nut/ Thread size on Glow Plug Electrical Connection M18

Discussion in 'Ask All Sailors' started by Loose Ends, Nov 13, 2017 at 7:27 AM. Add this thread to a FAQ

  1. Loose Ends

    Loose Ends

    Joined Feb 9, 2011
    54 posts, 0 likes
    Catalina 27
    US Forked River NJ
    Anyone know the thread size on the glow plug electrical connection nut. Dropped one somewhere under the engine yesterday. I could take the other one off to check the size, but my luck it will end up lost also.

    Thanks,

    Bill
     


  2. Michael Davis

    Michael Davis

    Joined Jan 5, 2017
    210 posts, 40 likes
    Beneteau First 38
    Ca Saturna Island B.C. Lyall Harbour Saturna Island
    If the M-18 is anything like the M-12 it will NOT start without glow plugs. It's been about 7 years since I rebuilt my M-12 and replaced the plugs. They were only about $12 Cdn each and came with the nut. I think 4mm. but you should have a couple of spares anyway. From any diesel place or Kubota dealer..... Universal tends to overcharge I think.
     


  3. jviss

    jviss

    Joined Feb 5, 2004
    1,984 posts, 121 likes
    Tartan 3800
    US Westborough Westport, MA
    I feel bad, I just threw out three burnt out glow plugs, with the nuts, which I had held on to for over 10 years! The nut is special, it's knurled, and there's a slot and an angle at the top into which you can insert a screwdriver.

    I found inexpensive replacement glow plugs at clubplug.net. Currently $5.65 for NGK-Y103K, the glow plug in the Universal M25, which is a Kubota D-850. The part from Universal is part number 299685, priced at $64.90 each. These are exactly the same.

    But, I digress. I suggest you buy a spare set, and use one of the new nuts. I have some spares, still, and will measure the thread on one a bit later.

    jv
     


  4. Loose Ends

    Loose Ends

    Joined Feb 9, 2011
    54 posts, 0 likes
    Catalina 27
    US Forked River NJ
    Yep, Knurled, little slot in the top. I guess since it is round that made it roll easier off the top of the engine.
    I will probably buy a spare and use the nut. But if a 10/24 8/32 etc will work, that would solve the problem.
    If you get a chance to measure I would appreciate that.
    Maybe I should just drop the other one and see where it rolls to LOL

    Bill
     


  5. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,370 posts, 328 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    The terminal nuts on many glow plugs, for Japanese engines, are metric. If the lower portion of the glow plug threads into a metric block the terminal nut on-top will also be metric.

    The most common size terminal nut I see for Kubota blocks is M4 X 0.7 pitch. Most glow plugs are usually use a coarse thread pitch not a fine pitch.

    I am not a fan of those older serrated thumb screws and much prefer a serrated flange nut as many glow plugs today will ship with, or a standard nut and lock washer if you can't find a serrated flange nut..

    If you don't want to remove the other nut just hit the hardware store and grab two metric nuts in M4 & M5 sizes and one of them will fit. It will cost you less than $1.00 to try. If I recall correctly NGK only has two terminal nut sizes they use for all their glow plugs and those are M4 and M5 if my memory is correct.
     


  6. Loose Ends

    Loose Ends

    Joined Feb 9, 2011
    54 posts, 0 likes
    Catalina 27
    US Forked River NJ
    Thank You for the metric info.
    I want to change them to a serrated flange nut as I believe it would afford a better electrical connection anyway.
    The knurled nuts just never seem to stay firmly in place in my opinion.
     


  7. jviss

    jviss

    Joined Feb 5, 2004
    1,984 posts, 121 likes
    Tartan 3800
    US Westborough Westport, MA
    I just measured it, I get M4x0.5, meaning, a 4mm diameter with 0.5mm thread pitch.

    I like the nut that comes with them, as one can use a screwdriver on them; that's what that slot is for!
     


  8. Loose Ends

    Loose Ends

    Joined Feb 9, 2011
    54 posts, 0 likes
    Catalina 27
    US Forked River NJ
    Thanks to all, I will buy a couple metric nuts (and a few spares) and get this taken care of.

    Bill
     


  9. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,370 posts, 328 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    Bill,

    I happen to be in the shop early today and am waiting on something to cure. I grabbed about six glow plugs from Kubota blocks or Westerbeke blocks, & some M4 and M5 nuts I had kicking around to try them out. while waiting for the glass to kick off.. I have 3 NGK glow plugs, 2 Champion glow plugs and 1 Beru. All of them take an M4 X .7 pitch nut. You should be pretty safe trying an M4 X .7. I also have a brand new 10mm NGK I just found, a Y-114T, and it is also M4 X.7... If your plug takes an M4 X .5 those nuts are "non-standard" stock for your average home center or hardware store. If yours are M4 X .5 these nut can be found at McMaster Carr or other specialty fastener suppliers such as Fastenal.
     


  10. jviss

    jviss

    Joined Feb 5, 2004
    1,984 posts, 121 likes
    Tartan 3800
    US Westborough Westport, MA
    It will be interesting to see. I measured the terminal thread on a NGK-Y103K. I didn't use my thread pitch gauge, but with a digital caliper across two threads I measured 1mm, as close as I could get with a magnifier. I'm not home now, but when I return I'll get out the metric pitch gauge and see.
     


  11. jviss

    jviss

    Joined Feb 5, 2004
    1,984 posts, 121 likes
    Tartan 3800
    US Westborough Westport, MA
    Maine is right, it's an M4x0.7.

    It turns out my Chinese metric thread pitch gauge is worthless! However, I measured again, by measuring the displacement of the nut over ten turns, and got 7mm. So, 1 thread = 0.7mm.

    jv
     



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