18MM sparkplug for lawn mower?

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Is it possible to get an 18MM spark plug for a lawn mower?
And does anyone have a brand/number for one?
The original plug was 14MM (a Champion RJ19LM) but it seems the previous owner drilled out the hole and it is now about 18MM. (I hope it is exactly 18mm, but I won't be able to tell until I buy a plug.)
The recommended 14MM plug has what I think is a short reach. The threaded part of the plug is 3/8" long, and if one includes the electrodes, the distance from underneath** the washer, past the threaded part, to the end of the ground electrode is 1/2".
**Maybe the "reach" is measured from above the washer. If so, both lengths should be 1/16 inch less.
I bought this Craftsman lawnmower second hand, and when I got home, the mower looked even nicer than I thought, but had no spark plug. I took plugs out of my two old mowers (which don't work or don't work well) and the hole was too big for them. I went to Sears and all the plugs they had for sale had the same size threads as the ones I had tried, 1/2 inch in diameter, which I guess is 14MM.
I think the hole is 18MM now.
Thanks
Meirman
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meirman wrote:

Similar thing happened to me when I purchased a used snowblower. Someone had stripped the plug threads in the head, as I discovered when I tried to start it up.
The most economical fix for me was to buy a new head, gasket and plug. IIRC it cost me less than $15 for all. A helicoil kit or getting a helicoil installed by a shop would have cost me more. <G>
Just my .02,
Jeff
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(W1BSV + Brass Rat '57 EE)
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wrote:

Someone has either drilled and tapped the hole for an old style Ford 18mm plug, or they have drilled and tapped the hole for a heli-coil insert and the insert has somehow come out.
The best option is to remove the head and have it repaired or replaced, using the correct spark plug.
-- Road Dog IBA#12795 '99 ST1100
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sounds like someone's already drilled and tapped for a HeliCoil and the insert came out. if you're friendly lawn mower mechanic won't loan you his tool kit and sell you a $2 insert, you can probably rent the HeliCoil spark plug tool kit. Hardware store sells a kit for $40 with a few different height inserts.
My mower shop guy loaned me his full HeliCoil kit with a healthy cash deposit and a promise to be right back. Free tips and tricks too.

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For the rest of us, what is a HeliCoil, and how does it work?
Thanks !!
--James--
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On 11/30/2004 6:20 PM US(ET), James Nipper took fingers to keys, and typed the following:

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Thanks for the link on the HeliCoil !!
Well, I learn something new every day !! Are these ususally available in places like Home Depot, Ace Hardware, etc ??
Thanks !!
--James--
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On 11/30/2004 8:59 PM US(ET), James Nipper took fingers to keys, and typed the following:

Probably an automotive store, like 'Advance' or 'Autozone' would be better.

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Of course it is. http://www.championsparkplugs.com /
Select "Search by Plug Construction" toward the bottom of the page. The owner's manual or listing for the original plug will give you the reach and heat range, look up the same or similar in an 18mm.
Note: Lawnmowers aren't real picky about heat range, just stay close to the original.
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meirman wrote:

Just find a similar mower / engine on the curb on trash day, and scavenge the head.
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Sure - just go to your local NAPA store and ask them for an 18MM Champion. Just make sure the length of the thread isn't longer than the thread on the original plug so it doesn't hit the top of the piston. I use them in tractors and I used to use them in my old snowmobiles. Should be about $1.75.

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wrote:

If it's a Briggs and Straton, their web site has a guide based on model number.
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meirman wrote:
<snippage> I

Use the head from one of the other mowers if it the same brand of engine. (and same or close horsepower rating.) Just compare them while they're off to make sure they are not different. You can probably even re-use the head gasket if you are careful taking it apart..
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Just weld it shut, then drill and re-tap the threads.
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"Oscar_Lives" wrote:

Um, he was looking for practical advice. Meirman, forget Sears, go to an automotive parts place like Autozone or small engine repairman. They should be able to help you.
- HPT
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On Fri, 10 Dec 2004 00:48:15 -0000, High Plains Thumper

That's quite practical if it really was drilled out and tapped.

Oh yeah, the minimum wage flunkies at sears or autozone would know what to do with a drilled out spark plug hole. NOT.

That would work. The small engine repairman would .... wait for it....
Weld it shut and then drill and re-tap the threads.
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Reason why I said *Autozone* is they *do* carry some small engine parts.

After there is no hope of finding a spark plug to fit ... and provide he has the tools to do it or some he *subcontracts* to do it.
Then it may be just as well to get another head from a small engine salvage shop (aka small engine repairman).
- HPT
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Or just repair the old head!
Hey, while you got it off, that would be a great time to mill it down and increase the compression for more power!

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"Oscar_Lives" wrote:

I've never seen a pimped lawn mower, may be a first!
- HPT
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<< The small engine repairman would .... wait for it....
Weld it shut and then drill and re-tap the threads. >>
Any machine shop would simply install a Helicoil. Takes 10 minutes, the part is $1.20. Done hundreds of them in everything from VW's to Mercedes. Simple.
Joe
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