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07-27-2020, 12:45 PM | #1 |
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Location: Akron, OH
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Compression Test Results
I have been trying to get my A going again after a few years of sitting around. It ran okay in the fall of 2015, but the following spring/summer, it was having issues going up anything but flat road and I didn't have time to really work on it.
I drove it up and down my road after getting it started last week, but had some pretty bad hesitation/missing under higher load/throttle in first gear. The last time I drove it around, I set the timing and gap on the points. It has a new ignition coil and the spark plugs are also basically new. I did a compression test on the engine because as far as I could tell, the ignition should be working correctly. The results weren't so great: Hot: 39/36/30/36 psi Cold: 40/35/30/36 psi Cold with a bit of oil: 40/35/35/44 psi These numbers seem quite low. Are they low enough to account for the poor performance in first great or should I re-check the ignition side of things? Maybe fuel related?
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-Noah 1931 Model A Pickup My Model A : https://www.fordbarn.com/forum/showthread.php?t=173024 |
07-27-2020, 12:59 PM | #2 |
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Re: Compression Test Results
Those compression numbers are low.
Make sure the coil polarity matches how you have the battery ground hooked up. Positive ground battery means the post marked with the + on the coil needs to be what is connected to the points in the distributor. Did you put in fresh gas? Our modern gas with ethanol does not age well. If 6 volt battery in car, is it a 6 volt coil? Accidentally putting in a 12 volt coil (with ballast resistor built in) gives a really weak spark on a 6 volt car. The carb may have some trash in the jets, preventing fuel from getting into the engine, so no power. Try blowing the jets out with some carb cleaner and then air. HTH.
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Jim Cannon Former MAFCA Technical Director "Have a Model A day!" |
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07-27-2020, 01:27 PM | #3 |
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Re: Compression Test Results
The compression are a bit low, but, even enough to be Ok especially if the car ran OK when put up a few years ago.
I'm with Jim about the fuel. Clean the system and add new fuel. The carburetor may need cleaning [ thats not hard if you have some compressed air.] There could be some sticky valves that could cause low power, rough running and misfires. Try adding [ mixed well] some SeaFoam, MMO, or 2 cycle oil to the fuel tank. Any of those may work. |
07-27-2020, 01:28 PM | #4 |
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Re: Compression Test Results
Hopefully you drain the old gas and using some good gas, I would put some Sea Foam and MMO in the tank and let it run. Slow idle first then a faster idle and rev it up ever so offen. Putting some MMO in the oil would hurt. I'am trying to get back in to shape after sitting around for a few months, your car has been sitting for years.
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07-27-2020, 01:30 PM | #5 |
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Re: Compression Test Results
I drained out the old gas and cleaned out the carb and made sure everything was clear and didn't have any blockages. I have a 6 volt coil with a new 6 volt battery. For the coil, the side marked (-) has 6 v on my multimeter when I use the head as a ground. Is that correct for polarity? Thanks for the quick reply.
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-Noah 1931 Model A Pickup My Model A : https://www.fordbarn.com/forum/showthread.php?t=173024 |
07-27-2020, 01:34 PM | #6 | |
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Re: Compression Test Results
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Quote:
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07-27-2020, 01:35 PM | #7 |
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Re: Compression Test Results
After looking at the ignition coil, the coil wire sheathing is pretty work out and breaking off in a couple spots. Maybe another issue? I will try to grab a video of the car running to maybe help diagnose.
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07-27-2020, 03:22 PM | #8 | |
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Re: Compression Test Results
Quote:
The post on the coil with the + next to it needs to be connected to the wire that goes to the points IF you have connected the battery up with the POSITIVE post to the ground cable. This is the original positive ground setup. Trace the wire coming off of the + post. Follow it to where it goes. And confirm that you have connected the battery up positive ground.
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07-27-2020, 04:01 PM | #9 |
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Re: Compression Test Results
The red wire off the + side of the ignition coil runs into the cab under the dash. Battery is connected + side to the chassis ground.
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07-27-2020, 04:10 PM | #10 |
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Re: Compression Test Results
Power to the coil goes to the - terminal. The + coil terminal should go to the ignition switch and on to the distributor/points[ if wired as original]. The coil is hot if switch is off or the points are open.
If the coil is wired backwards it'll still run. |
07-27-2020, 04:11 PM | #11 |
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Re: Compression Test Results
That should be correct. Red wire off + side on coil thru ignition switch to the distributor.
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07-27-2020, 05:04 PM | #12 |
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Re: Compression Test Results
Clean the oxidation off your points! Did you check compression with all the plugs, out for at least three revolutions with the throttle wide open.?
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07-27-2020, 09:55 PM | #13 |
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Re: Compression Test Results
You need to do something about the compression. Period.
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07-28-2020, 07:19 AM | #14 |
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Re: Compression Test Results
I agree, your compression is just about half of where it should be.
Think of your heart. If your blood pressure is in the toilet, your in trouble. Doesn’t matter how good you look. You can’t exercise, run, or even take long walks. You could also stop working at any time! Might be time to look at an overhaul. Enjoy. |
07-28-2020, 08:01 AM | #15 |
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Re: Compression Test Results
I forgot to have the other plugs out as I did the compression test. Re-did it and the results are slightly better, but still low: 46/44/36/46. Sorry about that. I guess overhaul of some kind might be in order.
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07-28-2020, 08:18 AM | #16 |
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Re: Compression Test Results
Did you open the throttle wide open? That will make a difference. I still think/hope that more running will get the compression up!
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Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done |
07-28-2020, 08:25 AM | #17 |
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Re: Compression Test Results
Let us know what you find, maybe you will be lucky and a valve job/head gasket replacement will be good enough. If you do not have them, consider consider adjustable lifters. Compression not rising with oil in the cylinders may mean the rings/cylinders are reasonable. Pulling and inspecting the Rod/Mains bearing caps and inspecting/checking/adjusting clearances may help as long as you are looking at things.
I am probably repeating info you already know, wishing you luck. |
07-28-2020, 08:36 AM | #18 | |
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Re: Compression Test Results
Quote:
Yes, WOT. Poured some Seafoam into the gas. Hopefully that helps. Will idle it and maybe try again today. Sent from my iPhone using Tapatalk
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07-28-2020, 08:58 AM | #19 |
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Re: Compression Test Results
Your compression numbers are horrible, so it's no wonder that engine lacks power. You need to correct the compression. Considering you have already run the engine, I doubt the piston rings are not doing their job.
If this car were mine, I would try adding a jar of Barr's Stop Leak with pellets. Follow Barr's directions. Let the engine cool to room temperature and check the compression again. If the numbers improve, you have compression leakages, perhaps from a corroded head gasket or pits in the head & deck surfaces.
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07-28-2020, 10:32 AM | #20 |
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Re: Compression Test Results
36 pounds compression? That thing won't pull your hat off.."overhaul in a can" is a joke...rebuild your engine
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