Dry compression test

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Jim Becker
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Re: Dry compression test

Postby Jim Becker » Sun Oct 25, 2020 10:40 pm

Rick Spivey wrote:. . . the only thing I read in all this is the possible engine knock on occasion. I'd probably try to pinpoint the cause of that, . . .

And if you have good oil pressure, I probably wouldn't worry much about that either.

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Glen
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Re: Dry compression test

Postby Glen » Mon Oct 26, 2020 6:34 pm

Hi,
The Cub service manual says a Cub engine has 120 lbs of compression. That is probably for a new engine. :)

k hutchins
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Tractors Owned: 1948 Farmall Cub
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Woods 59 C3
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Cub 172 one row planter
Original manuals for all the above
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Re: Dry compression test

Postby k hutchins » Wed Oct 28, 2020 5:02 pm

Thanks everyone.

Ricky, you must have been typing the same time l was or l woould have responded originally. This is my "Workhorse". Mows 5 acres weekly from Apr-Oct, then set up for snow plowing my 1/4 mi long drive that has a good up hill grade for half. It's rarely failed me. When l started going through a quart of oil (mostly leaking) each time l mowed, l realized it was time for TLC.

For everyone else, as l've said previously. This tractor has been in my family for 60 yrs, and l know it's never been overhauled or rebuilt except when something breaks, it gets fixed. Pistons, valves and every thing that attaches to them are all original.

I figure as long as l had to split it anyway, l'd replace some probably worn parts before they really go bad. Valve springs, keepers and guides. Main bearings, and possibly piston rings and bearings. That's why l did compression tests. It appears l don't need pistons or rings.

Oil pressure is good, but it's that knock in the lower end that makes me think main bearings at least.

I'll be going over everything else. Cleaning, adjusting, lubing, replacing original wire harness. I picked up another '48 months ago which has turned out to be a reliable replacement so far, but it's not my old reliable.

Thanks very much for the input and opinions, l'll keep ya posted on prgress. With pictures as l go.
Why is there never enough time to do the job right, but always enough time to do it over. :?:

tst
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Re: Dry compression test

Postby tst » Wed Oct 28, 2020 6:03 pm

if oil pressure is good main bearings are probably good, does it still have good pressure when hot? with the compression readings you have pistons/rings are good

k hutchins
10+ Years
10+ Years
Posts: 631
Joined: Tue Mar 27, 2012 5:48 pm
Zip Code: 48843
Tractors Owned: 1948 Farmall Cub
193 plow
1948 snow/grading blade
Woods 59 C3
Cub 144 cultivator
Cub 22 mower
Cub 172 one row planter
Original manuals for all the above
Circle of Safety: Y

Re: Dry compression test

Postby k hutchins » Wed Oct 28, 2020 7:17 pm

Tst
Oil pressure when at operating temp stays steady just above the red without droppping into the red. When cold at start up it starts out at mid range on the guage.

I'll be sipping the rear seal in about a week or 2.
Why is there never enough time to do the job right, but always enough time to do it over. :?:

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Glen
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Posts: 5495
Joined: Mon Mar 19, 2012 7:33 pm
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Tractors Owned: 1956 Farmall Cub with Fast Hitch, F-11 plow, Disc, Cultivator, Cub-22 mower
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Location: Wa.

Re: Dry compression test

Postby Glen » Thu Oct 29, 2020 12:55 am

Hi,
Everything sounds ok, except that you hear knocking sounds in the lower end of the engine.

Below is a page from the 1949 Cub operator's manual, showing what IH said about the oil pressure, at the lower right of the page.

http://farmallcub.com/rudi_cub/www.clea ... age-05.jpg

Another thing to think about, the oil gauge is from 1948, if it is the original, it might not be reading accurately nowadays.

I suggest checking the crankshaft bearings with Plastigauge, 1 or more bearing may be worn to the bigger end of the clearance shown in the service manual.
Measuring bearing clearances with Plastigauge is explained in the Cub service manual.
NAPA sells Plastigauge, in the area I live. There is red, or green, depending on the thickness needed.
You probably need the green.
Below are pages from the Cub service manual showing the running clearance for the crankshaft bearings. It says they are all .002" - .003"
There is also a crankshaft endplay spec, it is on the 2nd page. People on here have said it can make noise if it has too much endplay.

http://www.farmallcub.info/manuals/gss- ... 001-04.jpg

http://www.farmallcub.info/manuals/gss- ... 001-05.jpg

Knocking crankshaft bearings can make the crankshaft journals have a flat place, over time.
Then it needs the crankshaft ground, or if it is too bad, replaced.
Maybe you knew this already.


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