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.
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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,
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.
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
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.
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
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.
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
Reason why I said *Autozone* is they *do* carry some small
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
Then it may be just as well to get another head from a small
engine salvage shop (aka small engine repairman).
<< 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.
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