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Compression test blues.

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LRiddle
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Compression test blues.

Postby LRiddle » Thu Oct 27, 2016 9:36 pm

I did my compression test the other day, and I have to say, I am a bit puzzled. At first I did a dry test with the hood on, got lowsy numbers so I pulled the hood off to make sure I didn't pinch the guage's hose and to be sure I got a good seal. The numbers from the dry test are as follows:
1 - 90
2 - 60
3 - 80
4 - 50
The reason I say I am puzzled is that it's my understanding that with numbers that low the tractor should hardly drive, let alone be able to work. Yet I mow three acres a week with a woods 59 in second gear. It will mow in third gear as well if I could stand the beating it takes. So power hasn't seemed to be an issue for me.
Also, it doesn't burn oil or smoke at all. I haven't done a wet test yet, but I plan on it this coming week.
What are your guys' thoughts?
Luke Riddle
Tallmadge, Ohio
1951 Cub - Chesty



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havoc1482
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Re: Compression test blues.

Postby havoc1482 » Fri Oct 28, 2016 12:16 am

Valves not seating well? Air could be slipping past the valves on the compression stroke. That's my guess
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Eugene
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Re: Compression test blues.

Postby Eugene » Fri Oct 28, 2016 6:19 am

I would retake the compression tests, dry then wet.

As long as the tractor performs to your desires, I wouldn't do anything to the engine other than routine maintenance.

Compression will be higher with the engine running at idle or higher rpms than when the engine is being cranked over with the starter. My standard Cub only had 70 psi when purchased. I used the Cub for garden plowing for a year or two before I replaced the engine.

1951 Cub, hard telling how many hours are on the tractor, and when the engine was last rebuilt. Might want to save up some money for an engine rebuild. Winter project in a year or two.
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Re: Compression test blues.

Postby inairam » Fri Oct 28, 2016 6:22 am

First adjust the valves per the manual to take that out of the equation

Then do a wet test. Add a little engine oil in the cylinders.

RE do the compression test

If there is a change in compression it is rings.

If no change in compression it is valves.

You many want to try some "hope in a can" like seafoam or marvins or other oil treatments before you pull the head. One thing I did at the advise of my auto mechanic was pouring Seafoam directly into the cylinders and let it sit and keep redoing it. It helped on my 1949 it greatly reduced the blue smoke.

I agree with Eugune as long as the tractor id doing what you want do not get too concerned about the compression test numbers. Certainly do not pull the head or do a rebuild.

Adjust the valves, try some "hope in a can", run it a while, and redo dry and wet test, see where you are.
Last edited by inairam on Fri Oct 28, 2016 8:12 am, edited 1 time in total.
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Re: Compression test blues.

Postby ScottyD'sdad » Fri Oct 28, 2016 7:08 am

A cub engine will run on very low compression. My power unit that drives my corn grinder, was starting hard. Wanted to time it, but felt no compression, trying to find TDC. All four cylinder's rings were stuck, in the pistons, yet it ran, and did the job asked of it. Hard starting, and alittle smoke, were the only symptoms.
In your case, I'd expect valves. My standard answer, "it needs valve work. Last time the valves were touched, Eisenhower was president"
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LRiddle
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Posts: 488
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Zip Code: 44278
Tractors Owned: .
1951 Farmall Cub - Chesty

Woods 59 belly mower

54A blade

1956 Gravely L

Dozer blade

Tiller

Rotary Plow
Circle of Safety: Y
Location: Tallmadge, OH

Re: Compression test blues.

Postby LRiddle » Fri Oct 28, 2016 12:10 pm

Good suggestions guys, thank you. I will adjust the valves and re-do the test, dry and wet, and see what happens. I agree that as long as it's running fine and doing what I need, there isn't a need to tear into it just yet.
Perhaps the rings are just stuck and need a good cleaning. We'll see. I'll keep you updated. Thanks again.
Luke Riddle
Tallmadge, Ohio
1951 Cub - Chesty



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Matt Kirsch
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Re: Compression test blues.

Postby Matt Kirsch » Mon Oct 31, 2016 1:56 pm

If the valves were out of adjustment, or the rings were stuck, it would be down on power.

You state that you mow in 2nd and 3rd with a Woods 59 deck. I doubt if the tractor could even get the deck spinning with the compression numbers you got.

Thus I submit unto you that your compression readings are suspect. Either from improper procedure, or more likely from a sketchy compression gauge. The engine needs to crank over well; you can get one of these to fire and run if it's barely cranking over, but you won't get a good compression reading unless the starter really spins the engine over.


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