Michael Gent
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• Bixby, OK, USA |
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• Registered on 1/16/2003 |
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• 4 posts |
• 1 Vehicle
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 Posted:1/17/2003 17:41 |
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I did a compression test on a 5.8L Bronco engine in preparation for rebuilding it. The numbers I got seemed very low. Does anybody know what are good/normal compression readings? |
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E. Long
 
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• Subscriber since 1/1/2001 |
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• Atlanta, GA, USA |
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• Registered on 1/23/2001 |
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• 2,229 posts |
• 10 Vehicles
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Posted:1/17/2003 18:10 |
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| Quote: | | I did a compression test on a 5.8L Bronco engine in preparation for rebuilding it. The numbers I got seemed very low. Does anybody know what are good/normal compression readings? |
Where were your numbers at for each cylinder? How many miles are on the engine?
-Eric
'67 Galaxie 500 - 390 FE, .030" over, FE to AOD adapter, disc brake conversion. The Daily Driver.
'00 Excursion - 7.3L PSD, LANDYOT Gen-II Radius Rods, Factory Tech Valve Body, 200K+ miles and going |
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Michael Gent
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• Bixby, OK, USA |
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• Registered on 1/16/2003 |
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• 4 posts |
• 1 Vehicle
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Posted:1/17/2003 20:07 |
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All the cylinders are between 65 and 70. I'm not certain of the mileage on the engine, but it is around 160k. |
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Bob Lawrence
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• Pittsburgh, PA, USA |
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• Registered on 1/8/2003 |
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• 11 posts |
• 1 Vehicle
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Posted:1/17/2003 22:17 |
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The '84 351's didn't have extremely high compression to begin with. My books don't show a reading for a 1984, but the readings should be within 12-14 lbs of each other. You're within 5. That's pretty good. Now, if it feels like the engine doesn't have good compression, it's from normal wear, and all eight cylinders are wearing pretty evenly. It doesn't look like you have anything to worry about, especially if you're rebuilding it. |
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Michael Gent
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• Bixby, OK, USA |
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• Registered on 1/16/2003 |
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• 4 posts |
• 1 Vehicle
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Posted:1/17/2003 22:30 |
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Thanks a lot for the help. |
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Rich Boetsch
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• Watsonville, CA, USA |
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• Registered on 8/1/2002 |
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• 2 posts |
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Posted:1/18/2003 22:00 |
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The compression pressures stated are too low. If you have less than 125 lbs, there is a problem. With the pressures stated, it sounds like the timing chain has jumped time. |
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Bob Lawrence
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• Pittsburgh, PA, USA |
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• Registered on 1/8/2003 |
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• 11 posts |
• 1 Vehicle
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Posted:1/19/2003 15:31 |
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THE TIMING CHAIN???? If it had jumped time, it would be doing ALOT more than reading low compression!!! At 160,000 miles, 65-70 lbs sounds like it's worn out. |
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WD40
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• Helena, MT, USA |
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• Registered on 12/16/2002 |
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• 25 posts |
• 5 Vehicles
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Posted:1/21/2003 15:18 |
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Did you do the compression test cold, or after the engine was warmed up?
You also need to have the throttle plate fully open for a proper test.
Were all the spark plugs out, or did you pull 1 at a time?
I agree, it's a good thing that the numbers are as close as they are....but,
not a good thing that they're that low. 
My '85-5.8HO with 175,000 was running numbers between 110 and 115,
if that gives you an idea.
WD-40 Reverend GripShift |
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E. Long
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• Subscriber since 1/1/2001 |
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• Atlanta, GA, USA |
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• Registered on 1/23/2001 |
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• 2,229 posts |
• 10 Vehicles
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Posted:1/21/2003 23:26 |
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For comparison's sake as well, I did a compression check on the 390 in my '67 Galaxie. The engine just turned over what I think is 100,000 miles (assuming it has been accurate and not tinkered with throughout previous ownership) and was in the 135-140 range for all 8 cylinders.
-Eric
'67 Galaxie 500 - 390 FE, .030" over, FE to AOD adapter, disc brake conversion. The Daily Driver.
'00 Excursion - 7.3L PSD, LANDYOT Gen-II Radius Rods, Factory Tech Valve Body, 200K+ miles and going |
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