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Testing compression.

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LRiddle
5+ Years
5+ Years
Posts: 488
Joined: Wed Mar 02, 2016 11:57 am
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

Testing compression.

Postby LRiddle » Wed Oct 19, 2016 1:42 pm

I ordered a compression tester so I can see where I stand with the engine. It runs strong and will mow in 3rd gear if I could stand all the bouncing, but in order to have a better understanding of the tractor, I would like to know where it stands.

Would someone be so kind as to explain compression testing more to me? How it's done, wet vs. dry, and baseline numbers I should be looking for? I've seen snippets of it here and there, but haven't found a good walk-through on the process. I was hoping there would be something in the how-to section, but I didn't see it.

As always, thanks in advance for your replys.
Luke Riddle
Tallmadge, Ohio
1951 Cub - Chesty



"You can't believe everything you read on the internet." - Abraham Lincoln


Circle of Safety

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Eugene
Team Cub Mentor
Team Cub Mentor
Posts: 20336
Joined: Fri Jul 02, 2004 9:52 pm
Zip Code: 65051
Circle of Safety: Y
Location: Mo. Linn

Re: Testing compression.

Postby Eugene » Wed Oct 19, 2016 2:18 pm

Remove the spark plugs, ignition off. Throttle open, choke off. Dry test first.

Start at the #1 cylinder, minimum of 5 engine cranks/turn over. Record the compression reading.

Repeat on remainder of cylinders.

Squirt a tablespoon or bit more of oil into each cylinder, crank engine over. Repeat the test as described for the dry test.

If the compression numbers come up during the wet test - - rings. If the compression numbers remain the same/close to the same during the wet test- - valves.

Base line numbers. 120 psi normal. 70 psi poor. Variance is 10% difference between cylinders.

The simplest thing to do is post your compression test numbers. We will take a shot at interpreting your numbers.

OK. I purchased a 154 Numbered Cub. Dry compression test on cold engine was 105 psi, dead even on all cylinders. Didn't do a wet compression test because readings were not low enough to warrant the wet test or an engine rebuild.
I have an excuse. CRS.

User avatar
LRiddle
5+ Years
5+ Years
Posts: 488
Joined: Wed Mar 02, 2016 11:57 am
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: Testing compression.

Postby LRiddle » Wed Oct 19, 2016 2:29 pm

Perfect, Eugene, that's just what I was looking for. Thanks for taking the time to write that all out.

I'm getting the idea that if the numbers are up to snuff on the dry test then there isn't a need for the wet test. The wet test is for diagnotics, correct?
Luke Riddle
Tallmadge, Ohio
1951 Cub - Chesty



"You can't believe everything you read on the internet." - Abraham Lincoln


Circle of Safety

Eugene
Team Cub Mentor
Team Cub Mentor
Posts: 20336
Joined: Fri Jul 02, 2004 9:52 pm
Zip Code: 65051
Circle of Safety: Y
Location: Mo. Linn

Re: Testing compression.

Postby Eugene » Wed Oct 19, 2016 5:58 pm

LRiddle wrote:The wet test is for diagnotics, correct?
Correct. Both the dry and wet compression tests are fast and simple, telling you a lot about engine condition.

My opinion. Some of these engines are 69 years old, with untold engine hours. If you are going to open up engine to fix an obvious problem, better to rebuild the entire engine.
I have an excuse. CRS.

User avatar
LRiddle
5+ Years
5+ Years
Posts: 488
Joined: Wed Mar 02, 2016 11:57 am
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: Testing compression.

Postby LRiddle » Wed Oct 19, 2016 9:51 pm

Excellent. Thank you again. I'll post my results when I do the test.
Luke Riddle
Tallmadge, Ohio
1951 Cub - Chesty



"You can't believe everything you read on the internet." - Abraham Lincoln


Circle of Safety


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