Spark Plugs

Shawn in PA · Jun 12, 2011

SM got a pretty steady miss on #1 cylinder. Just did the head gasket about a month ago, and changed out the plugs, wires, cap, rotor, points ect. So I proceeded to check the manifold studs, and all were tight. Passed the propane test. I suspected a stuck valve, but after a compression check, it turns out that wasn't the case. All the valves were set to tolerance and still tight. No bent rods. Timing wasn't off either. Turns out, the new Autolite spark plug in the number 1 hole had failed... Swapped in a D-21 from my H and it purred as it should. Moral of the story, start with the simple stuff first, and don't assume new parts don't fail right out of the box...lesson learned. Shawn

Charlie M · Jun 12, 2011

I run D21 plugs in my H, M and 300U all the time. Today's gas needs a hotter plug and the D21 plugs have worked fine for me.

rustyfarmall · Jun 12, 2011

(quoted from post at 14:11:34 06/12/11) SM got a pretty steady miss on #1 cylinder. Just did the head gasket about a month ago, and changed out the plugs, wires, cap, rotor, points ect. So I proceeded to check the manifold studs, and all were tight. Passed the propane test. I suspected a stuck valve, but after a compression check, it turns out that wasn't the case. All the valves were set to tolerance and still tight. No bent rods. Timing wasn't off either. Turns out, the new Autolite spark plug in the number 1 hole had failed... Swapped in a D-21 from my H and it purred as it should. Moral of the story, start with the simple stuff first, and don't assume new parts don't fail right out of the box...lesson learned. Shawn

Did it fail? Or did it just get a speck of carbon bridging the gap? If you just recently had the head off, no doubt you loosened some of those carbon deposits in the chamber of the head and also on top of the pistons. That sort of thing will happen with any brand of spark plug.

F-Dean · Jun 12, 2011

I have had good performance from D21 spark plugs, too!

Owen Aaland · Jun 12, 2011

(quoted from post at 18:57:35 06/12/11) I have had good performance from D21 spark plugs, too!

I've also seen terrible performance from D21 spark plugs. It depends how the tractor is being used. On my I-2444 the work fine. that tractor seldom is run above half throttle and is used almost exclusively for loader work. In my Super C the sames plugs perform poorly. That tractor runs a six foot Woods mower so it is always running full throttle under a good load. D-21s will cause it to run on when shut off and also has preignition problems. You need to choose a plug that runs hot enough to keep the oil burned of the electrode but yet run cool enough not to cause other problems. Depending on how a tractor is used will determine which plug is best for you.

Shawn in PA · Jun 12, 2011

There was nothing bridging the gap of the electrode. It did have a very weak spark when I pulled it and grounded to the block. Swapped wires to verify that it wasn"t the wires. Also swapped dist cap and rotor too. I"m guessing it shorted internally. I"m not saying a Champion plug is better than an Autolite, or vice versa. I was simply stating that it occurred, with essentially an out of the box plug, for which I assumed would have performed properly. I just so happened to pull a D-21 from the H that was sitting one bay over.

Spark Plugs

Shawn in PA

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Charlie M

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rustyfarmall

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F-Dean

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Owen Aaland

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Shawn in PA

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