Jan 17, 2003 at 5:41 PM
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?
Engine and Drivetrain
84' 5.8L Compression
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Jan 17, 2003 at 6:10 PM
| 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
'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
Jan 17, 2003 at 8:07 PM
All the cylinders are between 65 and 70. I'm not certain of the mileage on the engine, but it is around 160k.
Jan 17, 2003 at 10:17 PM
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.
Jan 17, 2003 at 10:30 PM
Thanks a lot for the help.
Jan 18, 2003 at 10:00 PM
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.
Jan 19, 2003 at 3:31 PM
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.
Jan 21, 2003 at 3:18 PM
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.
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
edited Jan 21, 2003 at 3:19 PM
Jan 21, 2003 at 11:26 PM
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
'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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