compression test results
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Joined: Feb 2006
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From: Las Vegas, Nevada
compression test results
Hey, need a little help if you guys don't mind . I have a 54 ford truck but i'm working on a 289 mustang compression test . i was low in one cylinder 95lbs and held for ten min until i released it . i tried a wet test and went up to 150 just like the others. I've tested it four times since over 7 days and it holding at 150 . I'm thinking I didn't have gauge in all the way on first test. how long does it take for the oil to bled down after a wet test? Car was sitting for ten months and wouldn't run when i got it. I also had to put a starter in it and then a shim to get it running but i now have a thumping coming from the bell housing. any ideas would help.
bill
bill
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Joined: Oct 2009
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From: Burbank, WA
Personally, I wouldn't sweat the compression test. If it runs good and the numbers are consistent, you should be good to go.
The starter thing concerns me more. You should never have to shim a Ford starter. There are two different noses for the 289 starters used back then, one for manual and one for automatic. You could have the wrong starter, which would explain the need for shimming, and perhaps your noise if it's still hitting inside.
The starter thing concerns me more. You should never have to shim a Ford starter. There are two different noses for the 289 starters used back then, one for manual and one for automatic. You could have the wrong starter, which would explain the need for shimming, and perhaps your noise if it's still hitting inside.
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Joined: Apr 2016
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Like 52 Merc mentioned, the starter is concerning. If you install an auto trans starter in a manual trans, it will not disengage. A manual trans starter in an auto trans will not engage. Then there are the 157 and 164 tooth flywheel (ring gear) and matching bell housing arrangements. The 289 should be a 157 tooth setup unless a previous owner has changed it.
The few times I've added motor oil to a cylinder during a compression test, it has drained out fairly fast. After one or two compression tests things were back to the initial readings.
Here is a quick test us kind of old timers were taught to check for even compression. (1) Disable the ignition system by removing the coil wire from the distributor cap and connecting it to ground so there will be no arcing anywhere and it doesn't overheat the coil by trying to jump a huge gap. (2) Then with all spark plugs still installed, crank the motor several times. Listen to the cranking rhythm. If it is nice an even, all cylinders will have fairly close compression. If the cranking rhythm is uneven, there are one or more cylinders with low compression. This test was the first thing we would do when a car came in with a rough running engine and the customer asked to have it tuned up.
The few times I've added motor oil to a cylinder during a compression test, it has drained out fairly fast. After one or two compression tests things were back to the initial readings.
Here is a quick test us kind of old timers were taught to check for even compression. (1) Disable the ignition system by removing the coil wire from the distributor cap and connecting it to ground so there will be no arcing anywhere and it doesn't overheat the coil by trying to jump a huge gap. (2) Then with all spark plugs still installed, crank the motor several times. Listen to the cranking rhythm. If it is nice an even, all cylinders will have fairly close compression. If the cranking rhythm is uneven, there are one or more cylinders with low compression. This test was the first thing we would do when a car came in with a rough running engine and the customer asked to have it tuned up.
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