360 FE compression Q
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From: Alberta, Canada
360 FE compression Q
Evening all, My son any I are working on a 74 f100, original engine with 87600 miles. We got the old girl running and I wanted to check the compression, which was done with a rented compression gauge. I screwed it in with the hose and because of the design never got the hose super tight. Almost all the cylinders read 110 with one at 95 and one at 115. Would these readings be within the normal range?
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Is that with the carb WOT and cranking the engine over several revolutions to get the highest reading?
Did you try it again with a some oil in each cylinder?
When cranking the engine over, did you remove all the spark plugs or only the cylinder being tested?
Josh
Did you try it again with a some oil in each cylinder?
When cranking the engine over, did you remove all the spark plugs or only the cylinder being tested?
Josh
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From: Alberta, Canada
No oil in cylinders.
Removed one plug at a time and screwed in gauge.
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Carburetor has to be WOT for a decent test.
Helps to remove ALL the sparkplugs to help get a more thorough test as well. Reduces strain on the starter too and helps it spin faster.
If for some reason you do not want to remove the plugs, then remove the coil wire so the engine does not start.
Josh
Helps to remove ALL the sparkplugs to help get a more thorough test as well. Reduces strain on the starter too and helps it spin faster.
If for some reason you do not want to remove the plugs, then remove the coil wire so the engine does not start.
Josh
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From: Alberta, Canada
Carburetor has to be WOT for a decent test.
Helps to remove ALL the sparkplugs to help get a more thorough test as well. Reduces strain on the starter too and helps it spin faster.
If for some reason you do not want to remove the plugs, then remove the coil wire so the engine does not start.
Josh
Helps to remove ALL the sparkplugs to help get a more thorough test as well. Reduces strain on the starter too and helps it spin faster.
If for some reason you do not want to remove the plugs, then remove the coil wire so the engine does not start.
Josh
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Doing the compression test with closed throttle blades doesn't mean squat.
In reality, doing the test hot or cold doesn't mean anything either, other than burned knuckles. The only real numbers are a dry test and a wet test. That is compression with no oil and then another test with oil in each cylinder.
Josh
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From: Alberta, Canada
Redo the test with the carb at Wide Open Throttle.
Doing the compression test with closed throttle blades doesn't mean squat.
In reality, doing the test hot or cold doesn't mean anything either, other than burned knuckles. The only real numbers are a dry test and a wet test. That is compression with no oil and then another test with oil in each cylinder.
Josh
Doing the compression test with closed throttle blades doesn't mean squat.
In reality, doing the test hot or cold doesn't mean anything either, other than burned knuckles. The only real numbers are a dry test and a wet test. That is compression with no oil and then another test with oil in each cylinder.
Josh
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Hotshot
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From: Stanley, VA
With the throttle closed you are restricting the amount of air entering the cylinder. To be accurate the throttle needs to be wide open to get the maximum amount of air in the cylinder.
This is a test to see how well the cylinder can compress the air charge. It needs to have a full charge of air in the cylinder to be an effective test. Restricting the amount of air entering the cylinder can throw off the results.
Likewise on removing all the plugs, allows the engine to spin faster giving a higher, more accurate reading.
This is a test to see how well the cylinder can compress the air charge. It needs to have a full charge of air in the cylinder to be an effective test. Restricting the amount of air entering the cylinder can throw off the results.
Likewise on removing all the plugs, allows the engine to spin faster giving a higher, more accurate reading.
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From: Alberta, Canada
With the throttle closed you are restricting the amount of air entering the cylinder. To be accurate the throttle needs to be wide open to get the maximum amount of air in the cylinder.
This is a test to see how well the cylinder can compress the air charge. It needs to have a full charge of air in the cylinder to be an effective test. Restricting the amount of air entering the cylinder can throw off the results.
Likewise on removing all the plugs, allows the engine to spin faster giving a higher, more accurate reading.
This is a test to see how well the cylinder can compress the air charge. It needs to have a full charge of air in the cylinder to be an effective test. Restricting the amount of air entering the cylinder can throw off the results.
Likewise on removing all the plugs, allows the engine to spin faster giving a higher, more accurate reading.
Hotshot
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From: Stanley, VA
To do the test accurately you actually need to do it twice.
First, disconect and ground the coil wire. Then remove all eight spark plugs. Install the compression gauge in the first cylinder. Either hold or block the throttle wide open. Crank the engine over for five compression strokes and record the results. Repeat on the other seven cylinders.
Once that's done, repeat the test. Only this time squirt about a teaspoon of oil in each cylinder before the test on that cylinder, this is a wet test.
What this is is an indicator of how worn the rings are.
Usually the wet test isn't necessary unless you're trying to diagnose a cylinder(s) with abnormally low compression.
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From: Stanley, VA
Also, I don't have my shop manual handy at the moment but if memory serves me Ford's spec says the low and high cylinders should be within 20% of each other. 115 x .8 = 92
so you're within specs.
Rerunning the test should confirm with stronger numbers.
so you're within specs.
Rerunning the test should confirm with stronger numbers.
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