What is the spark plug thread for a 2N (compression test)

lastcowboy32

Well-known Member
I picked up a compression tester to help figure out my 2N's hesitation and why one plug is getting fouled.

I was previously told to get an elbow for the compression tester to make it easier to connect it without removing the gas tank.

What are the threads on a 2N head for the spark plug?
 

14mm Really? The compression tester has an adapter for that, but I was reluctant to use metric thread on an old tractor.

I wonder if it's just close enough to an English size to work.

I might have to experiment to get an elbow that I can put in-line with my compression tester, and I'm probably going to be hard-pressed to find an elbow with metric threads.

I have the hot plugs already; so I don't think that's an issue. Plugs are brand new, and my spark/timing and such is good. That cylinder must either have a piston/ring issue or a valve issue.

I've also noticed a little bit of oil/compression leakage at one of the head bolts. Assuming that the cylinder at the radiator is cylinder 1, the cylinder just behind it (2?) is the one that is fouling its plug. Just behind that plug, in the middle of the head, there is a head bolt that also helps to hold down the tube that holds the wiring harness (the tube that runs right over the center of the engine between the head and the gas tank).

That bolt has little tiny oil bubbles erupting around it when the tractor is running....maybe it just needs to be tightened...and I'm not sure if it's related to my plug fouling/hesitation issue.
 
I removed the ceramic from a sparkplug & brazed it to an el along with a "anti-fouler' adapter for the gauge to screw into.
 
(quoted from post at 15:40:03 11/16/15)
14mm Really? The compression tester has an adapter for that, but I was reluctant to use metric thread on an old tractor.

I wonder if it's just close enough to an English size to work.

I might have to experiment to get an elbow that I can put in-line with my compression tester, and I'm probably going to be hard-pressed to find an elbow with metric threads.

Experiment all you want but the threads are 14 x 1.25 mm and if you bugger them up you will be experimenting with a thread repair insert kit.

TOH
 
(quoted from post at 13:14:27 11/16/15)
(quoted from post at 15:40:03 11/16/15)
14mm Really? The compression tester has an adapter for that, but I was reluctant to use metric thread on an old tractor.

I wonder if it's just close enough to an English size to work.

I might have to experiment to get an elbow that I can put in-line with my compression tester, and I'm probably going to be hard-pressed to find an elbow with metric threads.

Experiment all you want but the threads are 14 x 1.25 mm and if you bugger them up you will be experimenting with a thread repair insert kit.

TOH

Well, that's why I came here to ask. I would have never in a million years thought of metric threads for a 1940's vintage American tractor. It also means that I can't just use plumbing parts. I like the idea of using old spark plugs and soldering to a plumbing elbow. That would guarantee that I don't ruin any threads.
 
(quoted from post at 16:50:52 11/16/15)
(quoted from post at 13:14:27 11/16/15)
(quoted from post at 15:40:03 11/16/15)
14mm Really? The compression tester has an adapter for that, but I was reluctant to use metric thread on an old tractor.

I wonder if it's just close enough to an English size to work.

I might have to experiment to get an elbow that I can put in-line with my compression tester, and I'm probably going to be hard-pressed to find an elbow with metric threads.



Experiment all you want but the threads are 14 x 1.25 mm and if you bugger them up you will be experimenting with a thread repair insert kit.

TOH

Well, that's why I came here to ask. I would have never in a million years thought of metric threads for a 1940's vintage American tractor. It also means that I can't just use plumbing parts. I like the idea of using old spark plugs and soldering to a plumbing elbow. That would guarantee that I don't ruin any threads.

I guess you will be even more surprised tolearn your1940's vintage tractor is full of metric parts ;-)

TOH
 

Touche'

Our other tractor is a 2000's vintage Chinese tractor. I call it "The Kung Pao." That friggin thing has metric, English and some bolts that you just clamp a vise-grip on and hope for the best.

I thought that I could get away from that with the old Ford, but I guess not.

This question has spurred me to do a little reading. All sorts of theories abound on the internet about why spark plugs are all metric. I throw my vote behind the fact that they were invented in Germany.

But really doesn't matter. All I know is that I just saved myself a whole lot of frustration and saved the tractor's head from a whole lot of abuse by asking.

:)
 
(quoted from post at 17:38:05 11/16/15)
Touche'

Our other tractor is a 2000's vintage Chinese tractor. I call it "The Kung Pao." That friggin thing has metric, English and some bolts that you just clamp a vise-grip on and hope for the best.

I thought that I could get away from that with the old Ford, but I guess not.

This question has spurred me to do a little reading. All sorts of theories abound on the internet about why spark plugs are all metric. I throw my vote behind the fact that they were invented in Germany.

But really doesn't matter. All I know is that I just saved myself a whole lot of frustration and saved the tractor's head from a whole lot of abuse by asking.

:)

The principal metric component you will encounter on the N-series is radial ball bearings - again invented in Europe and used by Ford. Off the top of my head I don't know of a single instance of an imperial series ball bearing being used. You will even find a very few components that are hybrids - e.g. metric shaft with an imperial thread pitch Ahhh - the good old days before we had real manufacturing standards. :roll:

TOH
 
(quoted from post at 01:17:09 11/17/15) I picked up a compression tester to help figure out my 2N's hesitation and why one plug is getting fouled.

I was previously told to get an elbow for the compression tester to make it easier to connect it without removing the gas tank.

What are the threads on a 2N head for the spark plug?

All the new testers I have seen in the last 41 years came with with a flexible hose that fits no mod's needed...

I googled a cheap P.O.S. gauge it even comes with a flexible hose...
http://www.harborfreight.com/compression-test-kit-8-pc-69885.html
 
Just for examples, Model T Fords had spark plugs with 1/2" NPT pipe threads. Model A Fords had spark plugs with 7/8"-18 fine threads.
 
hey Cowboy........check behind yer ears, are they still wet??? Compression has nuttin' to do with hesitation; thatza function of yer carbie. As fer elbow on yer compression tester, early el-cheepo compression testers used a rubber cone to fit straight in to yer sparkies hole. You might have noticed there is a gastank in the way fer a straight-in scheme. Modern compression testers now have a screw-in at end of flex hoze and kenn fit almost ennywharr .......HTH, Dell
 
Ford N-Series spark plugs: Champion H10, Champion H12, AutoLite 437, and other brands are 14mm x 1.25mm thread pitch. Don't think compression is your problem though...

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<font color="#FFFFFF" size="3">*9N653I* & *8NI55I3*</font>​
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Bruce,

I see what you mean. I have to look more closely at my compression tester. It has a number of adapters. One for 14mm, one for 18mm and one for "14mm long reach."

So, all of those will be metric threaded at one end to mate with the spark plug hole, but they may have an English thread at the end that mates with the compression tester. If that's the case, I could get an elbow with English threads to go between the adapter end and the tester.

Might work, and I saw your advice about taking the tester to the hardware store with me.

All good.

As for those who say that compression isn't the issue, I say, slow down. What could a compression test hurt?

I've gone through my ignition and replaced all of the parts that were screwing up my spark.

I have all new screens in my fuel system and excellent flow to the carb.

I don't have a stuck float.

I have adjusted my carburetor according to my F0-4 manual and some advice on here.

And yet, the engine starts a little harder than it should.

It sounds a little "chuggy" as if compression is coming out of the exhaust.

It has one spark plug that gets fouled. Doesn't smell like fuel, looks like oil.

It hesitates when the throttle is opened up or when it's put under load.

According to my F0-4 manual, this could be caused by a valve problem. All of the symptoms match up.

I don't like the black oily stuff on the spark plug; because that could be a ring problem with that cylinder.

Seems that a compression test wouldn't hurt.

I'm also keeping in mind a recent post by SoundGuy on another person's question, saying that, if it is a ring problem, I may not see a difference in my dry/wet compression tests; due to the oil already leaking past the ring making every compression test of the cylinder a "wet" test.

Thanks all for the help. It's sort of now become a mission of mine to make this engine purr.
 
" but they may have an English thread at the end that mates with the compression tester. "

No.

Not "may".

Will have.

Minimum acceptable pressure is 90 lbs w/ the lowest pressure reading w/in 75% of the highest reading. Run the engine to operating temp, turn it off, remove all 4 plugs, remove the breather hose & make sure the choke and throttle are both open. Crank it at least 5 compression strokes or until the gauge stops moving. Write down the first compression reading (that is the valves seating) then write down the reading after 5 strokes or when it stops increasing. You should have two numbers for each cylinder. Then, add a tablespoon of oil to each cylinder & repeat the process, but you only need the final reading for each cylinder. Write down the results & post back for help figuring out what it all means.
75 Tips
 
(quoted from post at 13:26:25 11/17/15) " but they may have an English thread at the end that mates with the compression tester. "

No.

Not "may".

Will have
75 Tips

When I do this, I'll post a picture of the business end of the compression test kit that I bought. It's kind of odd, with a double-stepped male thread on it...sort of like a 14mm male thread with an O-ring tacked onto the end of the 18mm male thread with it's own O-ring. There is no surface (like a hex or square) between the two threads that would allow me to easily take one out of the other...I'm also not sure if this little sucker is crimped onto the end of the hose, or if I can turn it off to find an English thread.
 
(quoted from post at 03:19:35 11/18/15)
(quoted from post at 13:26:25 11/17/15) " but they may have an English thread at the end that mates with the compression tester. "

No.

Not "may".

Will have
75 Tips

When I do this, I'll post a picture of the business end of the compression test kit that I bought. It's kind of odd, with a double-stepped male thread on it...sort of like a 14mm male thread with an O-ring tacked onto the end of the 18mm male thread with it's own O-ring. There is no surface (like a hex or square) between the two threads that would allow me to easily take one out of the other...I'm also not sure if this little sucker is crimped onto the end of the hose, or if I can turn it off to find an English thread.

You are making a project out of a simple test... The stepped end on yer hose will work screw it till the o-ring makes contact then snug by hand....
 
(quoted from post at 22:44:10 11/17/15)
(quoted from post at 03:19:35 11/18/15)
(quoted from post at 13:26:25 11/17/15) " but they may have an English thread at the end that mates with the compression tester. "

No.

Not "may".

Will have
75 Tips

When I do this, I'll post a picture of the business end of the compression test kit that I bought. It's kind of odd, with a double-stepped male thread on it...sort of like a 14mm male thread with an O-ring tacked onto the end of the 18mm male thread with it's own O-ring. There is no surface (like a hex or square) between the two threads that would allow me to easily take one out of the other...I'm also not sure if this little sucker is crimped onto the end of the hose, or if I can turn it off to find an English thread.

You are making a project out of a simple test... The stepped end on yer hose will work screw it till the o-ring makes contact then snug by hand....
eah, it is always easier to 'talk' than 'do'.
 
Better to talk first, so that damage done by the "do-ing" is minimized.

This isn't some project tractor. This isn't something that I'm getting paid to work on for the hundredth time.

I don't have the luxury of messing up; because down time equals manure piling up in the barn.

I also don't have the experience of having done this over and over and over.

I want a high probability of doing it right the first time.
 
(quoted from post at 18:18:04 11/17/15) Better to talk first, so that damage done by the "do-ing" is minimized.

This isn't some project tractor. This isn't something that I'm getting paid to work on for the hundredth time.

I don't have the luxury of messing up; because down time equals manure piling up in the barn.

I also don't have the experience of having done this over and over and over.

I want a high probability of doing it right the first time.

You have the hose with a combo 18/14mm fitting on the end and you have been assured the plug hole is 14mm. I don't know about you but I am darn sure screwing them together isn't going to "mess anything up" or cause you any down time ;-) Take the safety off and pull the trigger.....

TOH
 
You have the hose with a combo 18/14mm fitting on the end and you have been assured the plug hole is 14mm. I don't know about you but I am darn sure screwing them together isn't going to "mess anything up" or cause you any down time ;-) Take the safety off and pull the trigger.....

TOH[/quote]

Right. It will have to wait for the weekend, though. I use the tractor in the AM to clean the barn...off to work...then it's too late to fiddle around with it on a weeknight and ensure that it will be ready to go in the AM.

I have the starter off of our other tractor to have it rebuilt for the winter. So the old 2N is the lone ranger for the moment.

I studied my compression tester for a minute or two last night when I got home. That combo fitting is crimped onto the hose. There is no place to take it off to find an English thread for an elbow.

If I do try to rig up an elbow, it will need to have 14mm male thread for the spark plug hole and a 14mm female thread for my compression tester to go into.

My point is...if I hadn't posed this question, I would have never suspected a metric thread, and I would have been looking at English threaded elbows to make my life easier and would have possibly ended up cross threading something.

The hose on the tester is flexible, and there's a good chance that I can thread the combo fitting straight in and still get under the gas tank.

If it gets to be a pain, I have a couple of old spark plugs and such around. I can do the trick described in one of the previous responses to rig up a 14mm male to 14mm female elbow.
 

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