Spark plug gap goes to zero in minutes

drumgod828 · Jun 5, 2012

I have an s21esn and my spark plug gap goes to zero after a few minutes of running. What could be causing this? I already added a new plug and reset it a bunch of times. Now it looks pretty beat up (from the mower, not me)

scott47429 · Jun 5, 2012

sounds like theres something in that cylinder to me it could be as simple as carbon that has broke loose from the piston but i would pull the plug and look in there with a light you may have to pull the head

Mtn.Mike · Jun 5, 2012

Are you sure that the plug is the right length? It sounds as though the piston may be hitting the electrode.
Make sure that the plug is the right one and not too long.

Mike

Two-Stroke · Jun 5, 2012

Mtn.Mike said:
Are you sure that the plug is the right length? It sounds as though the piston may be hitting the electrode.
Make sure that the plug is the right one and not too long.

Mike

That sounds like the most likely explanation. I hope the piston isn't damaged.

scott47429 · Jun 5, 2012

if it was the piston hitting the plug the engine wouldn't run it would just hit and not start he said the plug gap goes away after running

drumgod828 · Jun 5, 2012

It is definitely not the plug. This started with the plug that I was using from last season and I had already used the mower a dozen or so times this year. The previous gallon of fuel I adding some seafoam and this gallon I added some marvel mystery oil to help clean out some carbon. I figured this would be easier than taking it apart and cleaning it manually. The carbon idea put forward earlier sounds like it might be the case. I think I am going to drain the fuel and take it apart to see what's up.

scott47429 · Jun 6, 2012

good luck let us know what you find

drumgod828 · Jun 6, 2012

As near as I can tell, part number 9 in this diagram: http://www.partstree.com/parts/disp...=0&ilIF=G&ilRE=8&ilSH=0&ilEG=0&ilRO=0&ilSC=21
came loose and entered the engine. The sides of the piston are pretty scratched up and BTW there was a ton of carbon. It's obvious the previous owner did little to maintain this mower. I suppose it's a testament to how good these mowers are.

Anyway I found several other issues including a bad ring, bad lower bearing and bad seals. I am going to completely rebuild it and I'm sure it will perform well for me again.

scott47429 · Jun 6, 2012

well that happens but at least you found the problem and now can fix it I'm sure it will be as good as new when your done let us know how it turns out and no alot of people don't maintain there mowers the way they need to

drumgod828 · Jun 8, 2012

Well it's done and running. I let a local shop hone the cylinder. Tally: new piston, new rings, new lower bearings, new seals-top and bottom, new drive pulley, went with a new carburetor, new spark plug, greased the drive section and pressure washed it. It looks amazing and runs very well.

Spark plug gap goes to zero in minutes

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