Compression Specs? Used or New Engine. - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 07-22-2009
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Compression Specs? Used or New Engine.

Hi Guys,

I'm getting a line of bs from Kar King that I bought my engine from. I had it diagnosed with cyl 2 giving 110 compression and the rest giving ~150. Kar King is trying to tell me that all the cylinders are giving mixed compression readings and that's normal for a used engine. I know it needs a head/valve job for sure but he just don't wanna do it under warranty and keeps feeding me bull****. I thought all the cylinders had to have at least 150 and if not then it needs a valve job.

Can anyone confirm?
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Old 07-22-2009
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Used engine? I thought it was rebuilt? If it was rebuilt then the rings would be replaced and the compression would be almost even across all cylinders.
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Old 07-22-2009
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Used Reconditioned Engine, not rebuilt.

Tell me if this makes sense to you guys, I found it on some site:

No cylinder should read less than 690 kpa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). Multiply the highest cylinder pressure by 70 percent, 1035 kPa x 70 percent = 725 kPa (150 psi x 70 percent = 105 psi), in order to determine the lowest allowable pressure in any other cylinder.


If this statement above is correct then I would take 160psi from the rest of my cylinders and multiply by 70% and that gives me 112 as the lowest any other cylinder can be. Therefor with 110 psi I'm still under the minimum it seems.
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Old 07-22-2009
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Also found this:

Maximum PSI Minimum PSI
134 . . . . . . . . . .101
136 . . . . . . . . . .102
138 . . . . . . . . . .104
140 . . . . . . . . . .105
142 . . . . . . . .. . 107
144 . . . . . . . . . .108
146 . . . . . . . . . .110
148 . . . . . . . . . .111
150 . . . . . . . . . .113
152 . . . . . . . . . .114
154 . . . . . . . . . .115
156 . . . . . . . . . .117
158 . . . . . . . . . .118
160 . . . . . . . . . .120
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Old 07-22-2009
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Compression should not vary more than 20% cylinder to cylinder. If two cylinders that are next to each other are low. You might have a blown head gasket or cracked head.
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Old 07-22-2009
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According to FORD's OEM Manual, Group 3, 303-00 in general information, it states the following:

The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading. For example, if the highest is 150 psi the lowest should be no less than 113 psi per Fords Compression Pressure Limit Chart.

However, two separate compression tests should be run (dry / wet) to determine what potential components, if any, are at fault.
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Old 07-22-2009
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Quote:
Originally Posted by Rev View Post
According to FORD's OEM Manual, Group 3, 303-00 in general information, it states the following:

The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading. For example, if the highest is 150 psi the lowest should be no less than 113 psi per Fords Compression Pressure Limit Chart.

However, two separate compression tests should be run (dry / wet) to determine what potential components, if any, are at fault.
Thanks Rev.

My highest is 160 and if I multiply that by .75 = 120 which = cylinder 2.

So I'm guessing at this point it's an acceptable low.
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Old 07-21-2010
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I was searching for some compression info for my Ranger, found this forum with this thread and thanks!! I have an '86 2.3L, EFI Ranger that just had the engine replaced after about 200K. For reference sake yesterday I did a compression test-Jasper Rebuilt-and it was 190, 190, 183, 192. Being a worrier I started wondering if that variation was OK. Only 200 miles on it. From these responses, it sounds as if I'm fine. Thanks again!
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