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Discussion Starter · #1 ·
3rd mowing this spring on an STX38.
She suddenly dies and after checking the majors, I discover that the new plug's ceramic has broken (sliding up and down the post. So, I replaced it and after starting up the same thing happens.

I pushed her back to the garage and am puzzling why this is happening. I don't think throwing in a 3rd plug is the answer. Do I need to clean out the cylinder before replacing the spark plug a 3rd time?
 

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I've never heard of the ceramic breaking from anything other than getting hit by something. Cleaning the cylinder head wouldn't have anything to do with it. Is there something out of place that might have banged the plug? It might even be that you just got two defective plugs in a row.
 

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motorhead is right, I would think if something internally was hitting, you'd REALLY KNOW IT!! :)
Might be a run of bad plugs. Where did you get them? Maybe someone dropped the box??
 

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Discussion Starter · #4 ·
puzzled owner of 2 broken plugs

Both of the prior plugs came from the kits JD sells. I made sure the gap was correct (040) and did not overtighten (there's a lock washer below the threads). The first broken one was from a new kit. The 2nd was the one I used all last season.

I have another plug -but am I risking serious damage to the cylinder and piston head? You would think that pieces of the ceramic would tear something up.

Thanks for the replies and any other insight.

p.s. I am a big Packer fan originally from Marinette, WI. Home of Mickey-Lu Bar-B-Q. Best darn burgers in the state - really.
 

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I'm going to second the notion that you got some bad plugs. Mind if I ask what brand they were?

Not to get too far off track, but you mentioned Marinette/Menominee, the gateway to the U.P. Go through there a lot and I've been to Mikey-Lu Bar B Q! I'll second what you said, they do serve up a pretty darn good burgers.

Speaking of good food, Schloegels in Menominee, MI has some good stuff on their menu, and looking out over Green Bay is pretty nice while you eat. Then Hereford and Hops in Escanaba serves up good food and micro brews. Travel a little further up on US 2 to Clydes in Manistique for the burger voted best in the U.P. For those with a hearty appetite, try the Clyde's Burger, 3/4 pounds of good eats.

Darn, all this talk about spark plugs has made me hungry.
 

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Discussion Starter · #6 ·
broken plugs

These are Champion brands(RC12YC) - right out of the kit.

The 2nd failed plug worked all of last season.

It seems unlikely that it would fail now all by itself.

I can put in the third - but I can't help but think that the broken pieces of ceramic are in the cylinder and that starting up will either pulverize the pieces or tear up the piston head.

By the way, I will be up there (WI) in July for some salmon fishing and will try the 3/4 pounder on the way - if you're gonna go - go big!
 

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They have small attachments for the shop vacs that have reducers and little hoses you can buy and you can use a piece of vacuum hose (Black-thin walled) and stick it in the spark plug hole and either suck it up or pull it out if it sticks to the end.
I have a set and they are handy ;)

 

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Discussion Starter · #8 ·
Shop vac to fix my Deere - like some fantasy repair!

I have to clean out the vac first so I'll know I grabbed something.

Again - this sounds like a natural mating ritual betwixt the garage occupants - ha!

Thanks, and I'll post my results.
 

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Discussion Starter · #9 ·
Broken plug solved with a hammer - really.

First offf - I want to thank you for your suggestions - they led us down the right path.

I walked across the way to my friend Nevio. He is Croatian and has lived in the US for most of his life. He is also one of the handiest people I know.

I showed him the plugs and he had me start the mower with the plug out - and he said he saw something spit out. (Yes - he had on safety glasses and was standing out of the line of fire.)

He said the only way to know was the pull the head off and look.

So, a dozen or so bolts later the piston is exposed and Nevio looks at me and says, "How are you running an engine on a bolt?" The cylinder head was kinda chewed up and had in imprint of some threads. He used a ball peen hammer to smooth things out. The valves were miraculously untouched! After reassembly - no dice until Nevio recalls that the cylinder may need to be in all the way - Voila!!
 

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By the way, I will be up there (WI) in July for some salmon fishing and will try the 3/4 pounder on the way - if you're gonna go - go big!
Make sure you're hungry before you order it. It's a family run place and most likely the owner will fry it up for you and his daughter will serve it. Good stuff, eh!

Glad things are looking up for the STX.
 

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Holy cow. Tough machines to put up with chunks o stuff rattling around in the combustion chamber.
 

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Discussion Starter · #12 ·
Tough machine indeed

After pounding out the dents, we reassembled and had to redo since we discovered that the cylinder needed to be all the way in the cylinder before it would start (valves out of sync?).

It is running but losing power when engaging PTO. I think my friend turned the idle speed screw instead of the fuel mix screw when adjusting the mix.

I need to find a sandbag so I can adjust the carburetor by myself (with the PTO engaged). As for the untouched valves - I am guessing they are made from a harder metal than the piston face and that is why they were untouched.

Still - I think many an owner would have just purchased a new one after seeing the damage. Maybe I am a little stubborn too....
 
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