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9n Not Starting. Low compression?

B

boxcheyvman

New User
Hi all!

I Just bought a 9N. The PO informed me that the engine had low compression and would not start. The PO did a full tune up and carb rebuild. I have hot spark and gas. The rotor roughly points to tdc.

When I got it home I put my thumb over all the holes and I couldn't keep it on there when I turned the the engine over so I was thinking it might have enough compression to run?

It will cough on either but it never catches. I just thought I would ask you guy what you think before I tear it all apart.
 
Tell us how you are checking for fuel and
spark. Use a compression meter to check
compression

What do you mean by "the rotor points to
tdc"?

The rotor is in the distributor which is on
the front of the tractor if you have a 9N.

TDC means top dead center which refers to a
piston.

Before you do anything, get a set of
manuals. See tip # 39.
75 Tips
 

Hey thanks for replying. I have the shop manual.

Im checking for spark with a spark tester and with a spark plug grounded to block. Nice big fat blue spark. I do not however have an open air spark tester just one with a light bulb that flashes.

Im going to borrow a compression tester tomorrow. I have read that its possiable for engines to run with 70 psi compression?

Rotor points to correct cylander at tdc using a wire to feel for tdc. This is rough estimate but i confident its in the ball park.

Thanks.
 
A simple thumb test say yes it has compression but how many pounds of compression does it take to make you not be able to hold your thumb on a plug hole?? Simple answer is not as much as needed for it to run and start like it should.You need to do a true and correct compression test both dry and wet. Anything less them 90PSI is to low for it to run well if at all
 
The fact that the PO did a full tune up and carb job before putting it up for sale as a non-running tractor makes alarm bells go off in my head. If poor compression was the
problem, why waste time and parts on a tune up? Was the machine running before the work was done? There are many opportunities while messing with the ignition and carb
to screw it up so it won't start. And these machines will run, if not well, on shockingly little compression, long enough at least long enough to do a good diagnosis and try out
some of the easier cures.
 
Need to do that compression test. But you can probably pull start it. I've got one that almost won't start once it's been setting for a long time. But once you do crank it, it cranks easy and runs fine.
 
Make sure that the valves are not sticking. A compression test will help to determine that. These old flatheads are notorious for that especially f you don"t use the tractor much.
 
I agree with Fuddy Duddy.
Pull start it!
Pour about 2 tablespoons of Marvel Mystery
Oil down each plug hole. Let it sit for a
day or two.
Then make certain you have good spark to the
plugs and fresh gas to the carb. You might
want to hook a temporary fuel tank like from
a lawnmower to insure a good flow of fresh
gas to the carb. Then hook a strap to it and
pull start it.
Put it in 3rd gear and pull it about 12 mph.
An old engine will almost Always start one
more time that way.
Once it has been run for a while it will
start again.
 

Ok compresion test time.

Cylinder 1 next ro rad-60
2-20
3-90
4-60

Then put 2 tsp of ATF.

1-120
2-60
3-100
4-110

I was like ok this is really bad. But it should run. So i tried starting fluid and after choking it and coaxing it it ran for a few seconds. In those few secconds it smoked out of the exhaust and crankcase and alot of back crud came out of the exhaust.

After few times of this the head was warm because i have the hood off and rad tank etc. So i decided to rerun a compresion test i dont know if you consider this dry or wet but here it is.

1-110
2-95
3-110
4-95

So im thinking valves were sorta stuck and the rings are worn. Really after i get it running i think a rebuild might be i order but im hoping to get a year of brush hogging out of it.
 
Boxer.........9N compression specs: 90psi min. Good runnin' 9N's run about 110psi. New overhauled engine about 125psi. Yeah, stuck valves and rings, good bet. Me? Runner like ya stole it. Change filter and oil in FALL. I use 20-50wt oil. .........oily Dell
 
If the tractor hasn't been run for a while
you are likely to have low compression
numbers. So IMO doing a compression test at
this point is mostly a waste of time.
Get the tractor running and go run the snot
out of it for a few hours - or days. And I
mean hard work like plowing or brush
hogging. Then if you want to check
compression you will get some meaningful
numbers.
Myself, I would be more interested in how
much it smokes and how much oil it uses.
As for a rebuild...
Over the years I have seen SO many of these
engines get rebuilt.
Half of them by newbies who thought they
could DIY and end up with a pile of junk and
the other half done by a professional shop
that charged them most of a couple grand.
Then, to go along with their rebuild they
get caught up in the restoration craze and
end up with 4 Grand +
in a tractor that has no live hydraulics,no
live PTO and on 9/2Ns, goofy brake pedals,
no real drawbar and no position control.
I know this board is all about Ns so saying
this will be an affront to some but you will
be much better off getting that tractor
running good and sell it to the next guy.
Then add the 2 Grand and buy a better
tractor.
Example:
I know where there's a Ford 650 that has
good tin and tires, runs good, fenders a
little rough but useable. Comes with a Ford
rear scoop, a 6' back blade and a near new
boom pole. Could be had for about 3 Grand.
A 650 has live hydraulics (not live PTO) and
is WAY more tractor than an N.
 
Numbers like the last set are encouraging. I too would run it for a while and see how it does provided it has decent oil pressure. You need to make it run reliably before additional testing can be done (lift function, tranny function). Since the numbers came up, I would change the oil and filter and determine if fuel and/or spark is causing the short run time.
 
I've got one that burns so much oil about every 4 gallons of gas you have to stop and clean the plugs and ad a quarts or more of oil.
But if I wanted to I could still get out there and bush hog with it.
It does still show 35# oil presser when hot.
I would change the oil and ad MMO and/or seafoam to the gas and oil. Then run it a while like that.
See what happens.
 
boxcheyvman,
When you compress air in a gas engine, the air is heated, like in a diesel. Without good
compression, the fuel/air mix will not burn properly. It's just that simple. Without good
compression, you have a warm weather engine.

Flat head engines used to burn valves, don't know why. Recently I had to grind the valves on a 20
hp kohler command. One cylinder would carbon up the plug, the other cylinder just fine. Both
cylinders shared the same carb. Compression tests 140 psi, leak down test, 95%, all good. But the
slightly burnt valve, under operation conditions, leaked enough pressure out the valves, there
wasn't complete combustion. I finally removed the bad head, lapped in the valves and now all is
fine. So even compression tests and leak down tests don't always tell the full story.

Now you have to decide do you want to rebuilt the engine?

I've always said if you want to buy a used car, do it on a very cold day and see how it runs.
 
One way to help an engine with low compression start is convert it to 12V. I would do that before spending big bucks on a rebuild.
Some guys hate to see an alternator hanging on the side of these tractors but it is a viable option.
 

Yep the tractor is already 12 volt and i did not have to pull start it to get it to run a bit so that is encouraging.

Its running out of gas and dying the spark is great, so im going to tear into the carb tonight.

If i can avoid a rebuild i can live with a smoking engine. i bought this tractor for 400 bucks thinking i would need to do a rebuild if i can get away from it i will be very happy.

I'm into boating and therefore very familiar with the idea of "if i just do this one thing it will be great" its best to just leave an old boat running OK than it is to spend thousands to get it to run only marginally better.
 
You are right, the faster you spin the engine, the warmer the air gets. I love alternators, have one on Jubilee and one on Farmall C. Only problem with Jubilee was the 6v starter drive would shear off when it was extremely cold. After two starter drives in sub zero temps and chipping a tooth on flywheel, I bought a 12v starter. Couldn't buy a 12v starter for Farmall C so I installed an old 12v 180CCA lawn mower battery. Both engines were rebuilt and have good compression. Problem solved. I'm a big fan of 12v tractors over the old 6v.
 
(quoted from post at 10:59:19 02/12/16)
Yep the tractor is already 12 volt and i did not have to pull start it to get it to run a bit so that is encouraging.

Its running out of gas and dying the spark is great, so im going to tear into the carb tonight.

If i can avoid a rebuild i can live with a smoking engine. i bought this tractor for 400 bucks thinking i would need to do a rebuild if i can get away from it i will be very happy.

I'm into boating and therefore very familiar with the idea of "if i just do this one thing it will be great" its best to just leave an old boat running OK than it is to spend thousands to get it to run only marginally better.
Click to expand...
efore you 'tear into the carb, verify flow through the sediment bowl valve's tiny passages, sediment bowl screens, and elbow at carb inlet screen. Remove carb bowl drain plug & see if it will flow enough to fill a pint container in 2 minutes or less. If it will, then all the above are OK. Might save you some time & trouble.
 
If you are starving for fuel, you should have a strainer in the elbow at the carb, a screen in the sediment bowl and a screen inside the tank on top of the sediment bowl.
The one in the tank only really protects the fuel going to the aux fuel when the shut off is all the way open. when the knob is only opened to the two turn setting, that stand pipe is not protected. I had one that the main stand pipe got plugged and it would only reun for 15 seconds or so. I ended up replacing the complete sediment bowl.
 

The PO bypassed the the tabk. Infact the tank isnt even on there. Its just a broken fuel line and temporary gas tank. So ill check flow and neddel valves.
 

Not in the snese your thinking. The choke plate is not bound up and the air filter unit is off.

But in order to get it to even catch i sprayed starting fluid into the barrel of the carb put my hand compleatly over the carb inlet and crank the tractor. I tried using my hand as a choke and depending on what the engine was doing i would give it more air or less.

Im honestly thinking the float is stuck or something simple.

I got great vacuum while cranking and running so i think my intake manifold should be ok. I dont see any cracks or leaks. And havent got it running long enough to test it any other way.
 

Well the tractor runs like a top now. I mean it smokes like a freight train but it runs good and starts easy.

It ended up being a stuck float that was also miss adjusted.

I just wanted to thank all the guys that gave me a hand, It was very appreciated!

While im here though I had one last question, Can I run a real heavy oil like 20W-50 to help seal these old rings up?

Thanks,
James
 
" Can I run a real heavy oil like 20W-50 to help seal these old rings up?"

I'd be afraid of bearing wear at a cold start w/ oil that heavy.

Please enlighten me on how the viscosity of oil is going to seal rings. That's a new one to me.
75 Tips
 
I do all the service on Mark's tractor (early 8N w/front mount dist). It is badly worn out, but with 12 V system and Minnesota cold (no heater), it does start. I know the engine has not had O.H. for the last 30 years, and maybe never. Compression is low and oil press hot is about 5 psi. You sure don't need much compression to start the thing even at 0 F. Good spark, valves acting as they should, fresh gas (even with ethanol!!), and the dang thing starts and runs. Mark is a special needs adult who has little knowledge of the mechanicals, little patience, and is strong as an ox. He used to shear off the rear wheel bolts by dropping the clutch until I took all the fluid out of the rear tires (reduced traction = less shock loading to the drive train). This tractor is used often (like a car) and abused all the time. I can't believe it still starts and runs with its low compression. I don't think these engines need any compression to start if the spark is set just a bit retarded.

Paul in MN
 
The heaviest I'd run is 15w40 personally, and if in arctic conditions, I'd drop that to a more energy saving oil.
 

Ok sounds good. The thought process was thick oil will have a harder time getting by the rings... maybe im the only one who thought that.

I have 30 psi oil pressure at a fast idle (i still need to fine tune the carb) and i know the PO cahnged to oil recently so i guess thats good.

I guess ill just leave it alone maybe run seafoam in the gas as others have sugested.

I live near st louis mo so its not artic but its definitely cold right now.

Thanks
James
 
I too am in Missouri the Lake of the Ozarks area and I run 20W-50 O'Reilly's brand oil which is Valvoline by the way year round in all but one of my machines. Never had any problem due to oil in the almost 36 years I have lived here. Only machine I do not run that oil in is my 1935 JD-B that was my grand fathers and in it I run 60W oil but it smokes very badly but it also has not been opened up since maybe the 50s if not longer then that
 
I pass threw St. Louis every week day.
I've all ways heard to run heavier oil in a worn engine too.
If you are going to let it set for a while, put some ATF in each cylinder.
More you let it soak the more the rings can loosen up.
 
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