compression test how to

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brewzalot
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compression test how to

Postby brewzalot » Sat Aug 19, 2017 12:17 pm

Cant find it- I'm sure there is a how to here somewhere?

Just getting started on my 57 Loboy restoration, it ran when I bought it 2 years ago but barely had enough power to get it on the trailer. Electrically has a lot of issues and I don't want to spend too much time getting it running again if the compression is the issue. I would start tearing it down now if that is the case.

Just looking for :
1. How fast and long do you need to spin the engine to be accurate? Only able to hand crank at the moment.
2. If you have skewed the dry test and already put in oil for the wet test is there a way to go back to the dry test?

thanks for any input

Tim

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Re: compression test how to

Postby Eugene » Sat Aug 19, 2017 1:42 pm

At least 5 compression strokes. So, hand cranking, 10 full hand crank revolutions, moderately fast. Your test readings will be lower than if you were using the starter.

The wet test will probably tell you everything you need to know, that you have or do not have sufficient compression to start the engine.
I have an excuse. CRS.

brewzalot
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Re: compression test how to

Postby brewzalot » Sat Aug 19, 2017 8:25 pm

Made a cranking shaft for an electric drill, at roughly 100-200 rpm 3 hours after adding oil.

1- 115
2-110
3-115
4- 112

What do you think of those numbers?

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Glen
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Re: compression test how to

Postby Glen » Sat Aug 19, 2017 8:51 pm

Hi,
The numbers are good, I would say. The Cub service manual says compression should be 120 lbs. That is probably for a new engine, not sure though.
You can use an oil additive like the guys on here have said, and it sometimes improves compression. Rings can get stuck from combustion over time, and an oil additive can help free them.
You have to run the engine for some time for it to help, and make the engine work too.

The older Cubs say 1800 RPM for the max speed on the serial number plate, this is a newer service manual, and says 2000 RPM. If you have a Cub that says 1800 RPM, use that. The newer Cubs don't say a speed on the plate, and should use what it says on this page from the manual.
Just wanted to say that, because the speeds are listed on the page. :)

http://www.farmallcub.info/manuals/gss- ... 001-04.jpg
Last edited by Glen on Sun Aug 20, 2017 1:08 am, edited 3 times in total.

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Re: compression test how to

Postby Bill Hudson » Sat Aug 19, 2017 8:57 pm

110 to 115 with an average of 113. In my book, those are good numbers.

Bill
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Re: compression test how to

Postby Eugene » Sat Aug 19, 2017 9:08 pm

Good numbers. At least you know the valves are not leaking.

Go ahead and start, then run the engine for a while, then conduct the dry compression test on a cold engine. Guessing the results will also be good.
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Re: compression test how to

Postby Barnyard » Sat Aug 19, 2017 9:16 pm

Those are great numbers for compression. Now here is my dilemma, I took a non-running Cub to DSCF in February and got it running with help from several forum members. The compression came in at 110 to 120 across all four cylinders. With those kind of numbers I knew I had to take it to the Cub Tug. Lo and behold, it died out within 5 feet of the line everytime it hooked to the sled.
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brewzalot
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Re: compression test how to

Postby brewzalot » Sat Aug 19, 2017 10:30 pm

Thanks all for your input-

Follow up question-

Every tractors history is different , but generally speaking, can a 60 year old engine still have great numbers without being rebuilt at some point?

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Mike in Louisiana
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Re: compression test how to

Postby Mike in Louisiana » Sun Aug 20, 2017 9:40 am

brewzalot wrote:Thanks all for your input-

Follow up question-

Every tractors history is different , but generally speaking, can a 60 year old engine still have great numbers without being rebuilt at some point?


It would depend on how many hours and how hard the engine was worked.
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and a lot of that comes from bad judgment. Will Rogers

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Re: compression test how to

Postby Matt Kirsch » Tue Aug 22, 2017 8:34 am

Barnyard, which line? The start line or the finish line?


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