48 cub , it runs....

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Zip Code: 81505
Tractors Owned: 1948 Farmall Cub
Location: Grand Junction Colorado

48 cub , it runs....

Postby ktinsley12091960 » Tue Mar 30, 2021 9:50 pm

Got the top off of my 48 cub this evening. See Pictures. Two of the plug holes had oil around them. When I ran the compression test they measured (front to back) 35,45,30,60 psi. I can start this tractor with a hand crank and drove it 2 miles. Should it even run with compression this low? I did the compression test by turning the engine over with the hand crank. Does this sound like a rebuild or a valve adjustment? :help:

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Don McCombs
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Tractors Owned: "1950 Something" Farmall Cub
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Location: MD, Deep Creek Lake

Re: 48 cub , it runs....

Postby Don McCombs » Tue Mar 30, 2021 9:57 pm

Put some Seafoam in the fuel and oil per the instructions on the can. Then continue to run it hard.
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Tractors Owned: 1956 Farmall Cub with Fast Hitch, F-11 plow, Disc, Cultivator, Cub-22 mower
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Re: 48 cub , it runs....

Postby Glen » Wed Mar 31, 2021 12:34 am

They have said on here that using the hand crank for a compression test turns the engine too slow.

They say use the starter.
Charge the battery fully first.
Remove all the spark plugs when doing the test.
Open the throttle fully so the engine can get air for the test.

The engine probably has more compression using the starter.

The Cub service manual says a Cub engine has 120 lbs of compression. That is probably for a new engine. They work with some less than that, about 90 lbs or more is ok.

The throttle rod is not in the clip at the rear of the head, in your pic. It needs to be securely in the clip, to keep the rod from flexing, so the throttle works right.
I would put the rod in the clip, and bend the clip mostly shut at the side closest to the bolt that holds it on the head.
Before bending the clip shut, I make sure the rod stays in about the position of where it would be in the clip, side to side.
Bend the rod right or left, if needed, so it says in about the right place by itself.
Hold the rod near the front end of it, if it needs bending, so it doesn't put force where the rod attaches to the governor arm.
Then put it in the clip, and bend the clip mostly shut.
Be sure the rod is loose some in the clip, so it doesn't bind.

While you have the hood off, I would oil the throttle arm pivot, at the governor, they commonly get tight on the pivot pin, from no lube. That is the arm the long throttle rod connects to.
Below is a pic from TM Tractor of the arm, oil it with motor oil where the cotter key is, and the other end of it also.

One of the experts on here said to use Seafoam in the oil for 2 oil change periods, to help free stuck piston rings, help oil burning, and help compression.
Seafoam is sold at auto parts stores.
The 1949 Cub owner's manual says change the oil every 120 hours of use.

If the rings are wornout, the additive won't help much.

I saw in one of your pics, I think, the Cub has silicone core spark plug wires.
They have said on here to use only solid copper core spark plug wires on a Cub.
I had a problem with the points in a Cub burning too fast, metal would move from one point to the other.
I asked at the Case IH dealer, the man I know there has been there for over 40 years.
He asked me, does the Cub have suppression spark plug wires, or resistor spark plugs, I said yes it has the resistor wires.
He said change it to solid core wires. He said the Cub ignition system was not designed for resistor core spark plug wires, or resistor spark plugs.
It makes the balance in the system wrong, and the points will burn, and metal will move from one point to the other.
I changed it to solid core wires.

TM Tractor has a new set of solid core wires, it say in their listing, if you have any interest. :)

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Re: 48 cub , it runs....

Postby radioguy41 » Wed Mar 31, 2021 5:23 am

You can't get any meaningful readings using a hand crank.
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