Spark Plug with No gap

[msengstock]

Hi, I was just doing the annual tune-up on my x728 (58 hrs) everything went fine up until I got around to replacing the spark plugs. One of the spark plugs had basically no gap. The side electrode was bent down touching the center electrode ... This is my first full on tune up, so its the original plug. I used the tractor during the winter for snow removal and did on ocassion (2 or 3 times) note a "clunk" coming from that side of the engine upon starting (one clunk as it started nott continuous as it ran), but never really noticed any loss of power at idle or full throttle or anywhere in between - I guess I wouldn't if the plug was that way all along. What could cause this - or could have it just always been that way?

Just curious. Oh and the plus was black, so there was some combustion going on it there I guess.

I did start up the engine and let it run with the new plugs in, and checked them - an they are still properly gapped so I'm assuming the piston isn't slamming into plug.

Thanks for any info.

 

[elad]

Probably got dropped on a hard floor at the factory and not checked by
the caring assembly person. There is a lot of those caring people alive
today. That's a shame too. elad

 

[greenmule]

Well its a good thing you checked them but why replace them at 50 some hours?

 

[ToadHill]

I'd put in a properly adjusted plug and run the engine for a while then check it again. If it happens again I'd call the dealer, it could be that the bearings are wearing, the connecting rod has streched , or the wrist pin has oblonged its hole in the piston.

 

[RWolf]

Also could be the wrong plug and is extended into the cylinder to far and the piston is hitting the tip just enough to bend it (clunk?). You could also have something floating around in the combustion chamber and the clunk could turn into a bang and broken mower.

 

[mfreund]

I would do a compression test on the cylinder. If it was not firing you could have had gasoline washing down the cylinder walls. The gas removes engine oil on the cylinder walls. This will cause compression loss.

If that cylinder had something in there you would already know
I agree with the dropped plug on assembly line.

Let us know what you find and what dealer says

 

[msengstock]

Good idea - I'll check the compression. At first I thought it was a case of the wrong type plug, but that wasnt the case.

 

[C-Range]

I can't believe it didn't make a noticeable difference in the running of the engine. Personally, I'd put that plug back into the plug wire socket, ground the body of the plug to the engine block, and crank the engine to observe the spark characteristics, if any. Maybe you were luckily getting just enough spark somehow to combust the charge.

Also, if the piston were striking the plug, odds are that you would see some kind of deformation in the metal. I'd clean all the soot off chemically (not mechanically) and look very closely at the tip of the plug for impact scars.

Further, consider looking down into the combustion chamber with the piston at TDC, and see if the piston has any marks on it. You might need a miniature flexible wand flashlight or something for illumination.

If there are any marks to be found, I'd raise holy **** with the dealer and demand a new machine. That's not a good way to start off a 20 year commitment. Chances are, though, the plug got damaged during assembly.

 

[msengstock]

Well, after looking alot closer the old plug had a very small hard to see gap - there was some spark, so it was probably just misfiring which might explain the occasional 'clunk' when starting it. Just ran it full throttle for 10 minutes and checked the plugs - the gaps are still good. Gotta think if it was hitting the piston, it would have already.

I do have to say now that the plugs are both gapped the same, it does run alot nicer and the the exhaust on startup isn't as rich (no black residue on the back of the loader bucket after starting) and the exhaust isn't nearly as smelly.

I'm guessing the fool that put it together on the assembly line missed the hole and slammed the plug against the engine (or dropped it) when putting it in.

 

[C-Range]

Great news. You might still want to do a thorough compression check to make sure everything is nice nice.

Nice machine by the way. I had the salesman writing up the paperwork for the 4WD/4WS version of one of those until I noticed the 2305 across the room and said, "What's thaaaat?!" The 728 was sure fun do drive around in the snow at the dealership though.