Case D Tractor Spark Plugs and compression numbers

primerk5 · Aug 3, 2016

The Plugs in my friends D are D-21 Champions. They had Anti Fouling caps installed on them. He is going to pick up new plugs this evening. What would the best plug be for this machine? I was reading online that D-21s were a hotter plug.

I see D-21 cross's to Autolite 386

What did they come with. I looked at the parts book and it has a case number I can't cross reference.

Also,

What compression should we expect from a good engine. We are seeing 110 lbs on every cylinder.

Thanks

oldproudvet · Aug 3, 2016

If plugs are fouling, and it isn't being used hard, go with a hotter plug. The actualy compression number isn't that important,
but the cylinders being close to ea other is. Cranking speed, carbon build up etc etc all enter into the actual number but if the
cylinders are with in 10% of ea other, you're good to go in that area

Klyde · Aug 3, 2016

If your going to use champs, use D-18Y. Projected tips last longer with crap gas.

John Saeli · Aug 3, 2016

Several things can cause fowled plugs, including ignition & engine internals. First & foremost, trash the Champions, & install Autolite 3116 Plugs. The 3116 Plugs are extended tip, non-resistor, whereas the 386 are resistor plugs. Also, check your wires, be sure you have copper core wires & not the "radio suppression", or "silicone" wires. Poor wires will fowl plugs. Resistor wires & resistor plugs will also shorten the life of a magneto.

primerk5 · Aug 3, 2016

I guess I should have said he just got this tractor. This is how it came and it hadn't run in a number of years. Previous owner just bought and resold it, so we don't know any history. I wouldn't say the plugs are fouling out. 3 of the plugs see ok just carboned some. the electrode on the 4th is eaten up some but it appears to had to much gap. I don't know if it really needed the anti fouling caps. That was the way we found it. I had never seen those before so we didn't remove them just in case they needed to be there. Will definitely go for a non resistor plug though.

It seems to run pretty good, but there is a miss every now and again.

Thanks for the help thus far.

1370rod · Aug 3, 2016

John is it OK to use the 3116 plugs as a replacement for all 386 CASE applications? Rod.

John Saeli · Aug 3, 2016

Rod: Never heard otherwise. Like I said, I prefer the 3116 because they are non-resistor, whereas the 386 plugs are resistor type. Bad for a Mag.

1370rod · Aug 3, 2016

Thank John, I will give them a try, Rod.

mEl · Aug 4, 2016

Been using Autolites for years since we had a run of fouling problems with the D16s which were the recommended plug for a lot of applications, I now use 3116 in everything that called for the D16. I use the 3116 exclusively even in performance applications after boring, stroking and raising compression. I find it interesting that Champ felt the need to go with different heat ranges in tractors that used to be D16. I was always a Champ man as were many of you but I feel that the change in gasoline in the 70s had something to do with it.

primerk5 · Aug 4, 2016

Couldn't find autolites locally in stock, so he settled for champions for now. It is running much better. We are seeing oil in the cylinders. (plugs are wet) It runs with very little smoke though. We don't know how long it has been sitting without running. Perhaps its just stuck rings.

Looks like we might have to pull the top off the transmission eventually. It gets stuck in gear some how and won't come out of reverse right away. within a couple of seconds of fiddling we can get it out of reverse.

Case D Tractor Spark Plugs and compression numbers

primerk5

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oldproudvet

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Klyde

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John Saeli

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primerk5

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1370rod

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John Saeli

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1370rod

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mEl

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primerk5

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