Question about valve clearance 8N front mount

[HeyObie]

Been having problems with my 8N for a couple years. Used to run great. Does not have enough power to run my 5" mower. It is not electrical. It had the problem when it was 6 volt. Switched to 12V because I could never get the regulator and generator working. New wiring. Fried points and square coils. So I went to electronic ignition. New plugs, new copper plug wires, new cap, new rotor and new distributor. Still ran the same.

Been through 3 carbs and 2 fuel shutoffs. Still ran crappy.

I had checked the compression before I started all that and it seemed fine to me. Just checked it again today. All 4 cylinders would pump up to 110 cold on the 4th cycle (30, 60, 90 then 110).

The plugs always looked good to me, but when I pulled them again the other day, number 1 did not look so good (dark from bad combustion). 2 and 3 and 4 looked clean and good.

So I measured the valve clearances. My understanding is that COLD, Intake valves should be .12-.14 and Exhaust should be .14-.16 Here are my readings from 4 cylinder to 1 as if you were looking at the engine:

4 (E-.14 I-[color=red:2242102600].15[/color:2242102600]), 3 (I-.[color=red:2242102600]15[/color:2242102600] E-.16) 2 (E-.16 I-.12) 1 (I-.[color=red:2242102600]16[/color:2242102600] E-.[color=red:2242102600]18[/color:2242102600])

So cylinder 1 looks bad.

SO here is my Question. If the exhaust valve on #1 has a gap of .18, would that mean that the compression is good because it is not opening and since the cylinder can not rid itself of exhaust properly, it may have problem igniting since the cylinder is full of exhaust?

One of my symptoms was igniting in the exhaust pipe. Would this explain it?

Thanks, Obie

 

[R Geiger]

0.002" over the max is not very much and I don't think it would effect the compression you are getting. I don't like the low compression reading you are getting at first. been awhile since I have checked one but that don't sound right.
number one is the one closest to the radiator by the way.

 

[HeyObie]

I agree Cylinder 1 is closest to the radiator. I am showing from left to right as if you are looking at the tractor. The gap is off .02 not .002... is that significant? I think the compression takes a second to build up because it is filling up my gauge and hose.

 

[Gantt]

my valves or about the same as yours measured. slightly out. i have not used any equipment other than a disc harrow with mine but it seems to run ok. i would not think this was a valve lash issue

 

[Duner Wi]

Just to be clear. What you write is .180 thousands for # 1 ex.Do you mean .018 thousands or do you really have .18 hundreds of an inch. Big difference. Honest I not trying to cause trouble.

 

[R Geiger]

(quoted from post at 12:33:25 04/13/20) I agree Cylinder 1 is closest to the radiator. I am showing from left to right as if you are looking at the tractor. The gap is off .02 not .002... is that significant? I think the compression takes a second to build up because it is filling up my gauge and hose.

Do believe you should revisit the FO-4 service manual.
Tappet clearance (gap) should be 0.010-0.012" for intake and 0.014" to 0.016" for exhaust! If it is off by 0.020" you have problems.

 

[HCooke]

"The plugs always looked good to me, but when I pulled them again the other day, number 1 did not look so good (dark from bad combustion). 2
and 3 and 4 looked clean and good."

What spark plugs are you using? Might want to try new plugs. I recommend NGK 3112 over autolites. Your compression numbers seem ok to me.

 

[HeyObie]

I am sorry. My decimal point is off. You were correct. .018

Plugs NGK B4L

 

[Eman]

A few thousandths difference isn't going to make a tremendous difference. I'd say most N series mine included haven't had the valve clearance checked in decades. Your compression looks great and the way it pulses up is normal. You should have the throttle wide open when checking as you're measuring compressed air and if the throttle is closed it restricts the air entering the cylinder. My 8N has 1 cyl with low compression and it still pulls my mower and bushhog with no problems.

 

[HeyObie]

I have the intake/exhaust manifold off because i was going to pull the head so there is no intake restriction when i did the compression test. I am at such a loss. These tractors are so forgiving.

I am missing something obvious.
3 carbs, 2 fuel filter cutoffs, 6 volt to 12 volt to electronic ignition, new plugs, new wires, good compression, firing order 1,2,4,3.
New manifold gaskets, no visible cracks on exhaust manifold

It has more power when i pull the choke out about 1 inch which to me means that i am reducing air to the cylinder to make the mixture rich. hear gas firing in the exhaust pipe at times.

 

[HeyObie]

I have the intake/exhaust manifold off because i was going to pull the head so there is no intake restriction when i did the compression test. I am at such a loss. These tractors are so forgiving.

I am missing something obvious.
3 carbs, 2 fuel filter cutoffs, 6 volt to 12 volt to electronic ignition, new plugs, new wires, good compression, firing order 1,2,4,3.
New manifold gaskets, no visible cracks on exhaust manifold

It has more power when i pull the choke out about 1 inch which to me means that i am reducing air to the cylinder to make the mixture rich. hear gas firing in the exhaust pipe at times.

 

[a32vickyhotrod]

Ignition timing can effect power, and or the mechanical advance weights, also cylinders 2 and 3 plug wires being switched. Have you checked these items?
Is the engine acting like it is missing or running smoothly? Have you checked the governor to see if it is working properly?

 

[jimtrs]

(quoted from post at 11:46:42 04/15/20) I have the intake/exhaust manifold off because i was going to pull the head so there is no intake restriction when i did the compression test. I am at such a loss. These tractors are so forgiving.

I am missing something obvious.
3 carbs, 2 fuel filter cutoffs, 6 volt to 12 volt to electronic ignition, new plugs, new wires, good compression, firing order 1,2,4,3.
New manifold gaskets, no visible cracks on exhaust manifold

It has more power when i pull the choke out about 1 inch which to me means that i am reducing air to the cylinder to make the mixture rich. hear gas firing in the exhaust pipe at times.

First things first
STOP buying stuff you probably don't need.
Valve clearances you state are not your problem. Stop overthinking it. Valve clearances are problems when non-existent, or WAY too large.

It is not electrical. It had the problem when it was 6 volt. Switched to 12V because I could never get the regulator and generator working.

You say not electrical, but how do you know this. Just changing parts does not rule out the entire spectrum of electrical. 12 volts from 6 volts will have very little to no impact on how well your tractor runs. That changes the charging system, not the ignition system. Though as you found out, some changes do need to be made to the ignition system when going to 12 volts, hence your fried coil.

One of my symptoms was igniting in the exhaust pipe. Would this explain it?

How do you know your backfiring into the exhaust pipe? This can be caused by a variety of reasons:
Firing order wrong (easy to do with a front mount)
Ignition timing too far off (hard to next to impossible to do with a front mount)
NO Valve clearances (Sounds like you got clearance)
Valves Sticking (very possible)

I was going to pull the head so there is no intake restriction when i did the compression test

[b:2022a478d5]Stop and don't do it![/b:2022a478d5] Extremely unlikely there will be anything you will need to do there, and troubleshooting comes to a stop with the cylinder head removed. With your manifold off, make sure it is good (no leaks between intake and exhaust portions)

It has more power when i pull the choke out about 1 inch

Huge clue! As you state this makes your fuel mix rich. Just cause you changed carbs DOES NOT rule out fuel issues. Carbs need to be adjusted properly and cannot be sucking air anywhere except through the throat of the carb. Carb mount to manifold and manifold to cylinder head are likely areas to be sucking air. That would make for a lean mix. Lean mix can cause heat, in turn causing a host of other problems backfiring, burning up spark plugs, overheating etc.

110 for compression (if correctly done) are great numbers to have.

Time to stop for a moment, re-think your troubleshooting, and start diagnosing again.

CALLING @Bruce(VA)

 

[HeyObie]

Ignition timing can effect power, and or the mechanical advance weights, also cylinders 2 and 3 plug wires being switched. Have you checked these items?
Is the engine acting like it is missing or running smoothly? Have you checked the governor to see if it is working properly?

I have moved the timing all the way advance all the way retard and in the middle has some effect but is not the problem.

I have the top of the tractor off - gas tank. The wires are clear as day. Cylinders from radiator to back of tractor are 1,2 3,4. Wires on distributor cap go counter clockwise 1, 2, 4, 3 as marked in distributor cap

Engine fires right up. Idles fine but really likes me to hold the choke. Must hold choke longer than i am used to. This is my second 8N. Owned 8Ns for 33 years. when i give it more gas it takes it but hesitates but will rev up.

I feel it is fuel mixture related. Improves when choked. On level ground, i can drive the mower and get it up to speed if i choke it. But it is weak as a kitten. If i go uphill with mower running it will crap out.

I do not know how to check the governor. It responds when i give it full throttle

As far as spark is concerned, it looks solid to me. I have a spark tester. I tested again today. I set the gap at 1/4 inch. Testsd each cylinder. Consistent across all 4. Solid WHITE spark.

 

[a32vickyhotrod]

Sounds like you have covered all the bases on this one. That choke thing gets my attention. I would bring your RPM's up to full throttle and turn out the high speed jet until it starts to stumble and then take it for a ride and see what the power level is under load.

 

[soaked]

Are you using an aftermarket Marvel
Schebler clone carb? If so, it may have
the wrong economizer jet. If a 1/16 th
drill bit will pass through the jet, its
too big.

Spec is 9n9914 and is .046.

Will start and run ok to 1/2 throttle,
then struggle, surge, because of lean
condition caused by the wrong jet for a
8n.

In the pix, the screw driver shows the
port the jet is located.
Zoom in to see the jets on the wires.

John

 

[HeyObie]

Jim,

Gotta go get dinner but will respond to your items. As far as air leaking into the system, this is what I did last year. I pulled the manifold. I have a large table belt sander. I put the manifold on there and ground it done until everything was clean as a whistle. I took a single edge blade to the block and cleaned well. Got new gaskets for the engine side and carb side. I put high heat sealant on it (i know that may not be right thing to do, but wanted to fill any gaps). No difference.

I do not see any problems with the manifold. Looked at it real hard 5 minutes ago. No visible cracks. It is really hard to see what is going on inside where the intake and exhaust meet.

I just remembered that I tested it last year (i have it off right now). What I did last year was to pour water into the intake ports and see if it leaked down. The water levels did not move, so I assumed it was good. I will try again.

When I get back I will describe the gradual degredation of the tractor and where I am now

 

[HeyObie]

When I could not figure out the problem and my guess was carb, I bought one from this site. After a year or so passed (been limping along for 3 years with this problem), I read that some of these carbs can cause problems. So I bought another one to see if I got lucky. So I bought another one from this site. Same results. I even adjusted the float to put more fuel into the bowl. Nope

I will check on the orifice size,

 

[kossuth]

(quoted from post at 09:27:13 04/15/20)

(quoted from post at 11:46:42 04/15/20) I have the intake/exhaust manifold off because i was going to pull the head so there is no intake restriction when i did the compression test. I am at such a loss. These tractors are so forgiving.

I am missing something obvious.
3 carbs, 2 fuel filter cutoffs, 6 volt to 12 volt to electronic ignition, new plugs, new wires, good compression, firing order 1,2,4,3.
New manifold gaskets, no visible cracks on exhaust manifold

It has more power when i pull the choke out about 1 inch which to me means that i am reducing air to the cylinder to make the mixture rich. hear gas firing in the exhaust pipe at times.

You say not electrical, but how do you know this. Just changing parts does not rule out the entire spectrum of electrical. 12 volts from 6 volts will have very little to no impact on how well your tractor runs. That changes the charging system, not the ignition system. Though as you found out, some changes do need to be made to the ignition system when going to 12 volts, hence your fried coil.

How do you know your backfiring into the exhaust pipe? This can be caused by a variety of reasons:
Firing order wrong (easy to do with a front mount)
Ignition timing too far off (hard to next to impossible to do with a front mount)
NO Valve clearances (Sounds like you got clearance)
Valves Sticking (very possible)

Stop and don't do it! Extremely unlikely there will be anything you will need to do there, and troubleshooting comes to a stop with the cylinder head removed. With your manifold off, make sure it is good (no leaks between intake and exhaust portions)

Huge clue! As you state this makes your fuel mix rich. Just cause you changed carbs DOES NOT rule out fuel issues. Carbs need to be adjusted properly and cannot be sucking air anywhere except through the throat of the carb. Carb mount to manifold and manifold to cylinder head are likely areas to be sucking air. That would make for a lean mix. Lean mix can cause heat, in turn causing a host of other problems backfiring, burning up spark plugs, overheating etc.

110 for compression (if correctly done) are great numbers to have.

Time to stop for a moment, re-think your troubleshooting, and start diagnosing again.

CALLING @Bruce(VA)

ITTO..... You most likely have a fuel air/carb issue. But you need to check a few other things quickly to rule them out.

It s unlikely but you could have a leaking intake manifold gasket. Take a propane torch "unlit" and pass it around the flange of both the engine block and carb base. If the engine changes it s behavior with propane passing by a flange you have the problem.

This is also unlikely but make sure your spark is good and strong. A strong spark will have a light/bluish color to it. If the spark is yellowish that indicates the spark is weak spark and choking the motor helps light off the fuel mix due to the weak spark.

After you check the two above items out and come to the conclusion both are ok then we can get serious about your carb issue. The carb likely either has the wrong jets installed or a passage is blocked. The carb needs to be:
1. Completely stripped
2. Check all the jets and replaced if found to be wrong size
3. Run a very fine wire through the passages. Don t force anything.
3. Run the carb and all the parts/pieces for about an hour in a ultrasonic cleaner and when complete blow out everything with compressed air. Those dunk tanks just don t have the cleaning power they used to.

After this check your fuel tank and make sure it s not flaking rust inside. If so you need to deal with that ASAP because you ll be right back in the carb if you don t.