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Old 07-27-2020, 12:45 PM   #1
31pickup650
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Default 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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Old 07-27-2020, 12:59 PM   #2
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Default 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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Old 07-27-2020, 01:27 PM   #3
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Default 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.
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Old 07-27-2020, 01:28 PM   #4
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Default 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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Old 07-27-2020, 01:30 PM   #5
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Default 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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Old 07-27-2020, 01:34 PM   #6
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Default Re: Compression Test Results

Quote:
Originally Posted by Patrick L. View Post
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.
The car wasn't running so well when I put it away. I may need to try some of the Seaform type stuff in the fuel. Pretty sure I have a can sitting around.
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Old 07-27-2020, 01:35 PM   #7
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Default 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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Old 07-27-2020, 03:22 PM   #8
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Default Re: Compression Test Results

Quote:
Originally Posted by 31pickup650 View Post
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.
No. That's not what we are talking about.

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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Old 07-27-2020, 04:01 PM   #9
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Default 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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Old 07-27-2020, 04:10 PM   #10
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Default 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.
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Old 07-27-2020, 04:11 PM   #11
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Default Re: Compression Test Results

Quote:
Originally Posted by 31pickup650 View Post
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.
That should be correct. Red wire off + side on coil thru ignition switch to the distributor.
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Old 07-27-2020, 05:04 PM   #12
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Default 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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Old 07-27-2020, 09:55 PM   #13
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Default Re: Compression Test Results

You need to do something about the compression. Period.
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Old 07-28-2020, 07:19 AM   #14
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Default Re: Compression Test Results

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You need to do something about the compression. Period.
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. Doesnít matter how good you look. You canít exercise, run, or even take long walks. You could also stop working at any time!

Might be time to look at an overhaul.

Enjoy.
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Old 07-28-2020, 08:01 AM   #15
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Default 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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Old 07-28-2020, 08:18 AM   #16
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Default 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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Old 07-28-2020, 08:25 AM   #17
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Default 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.
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Old 07-28-2020, 08:36 AM   #18
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Default Re: Compression Test Results

Quote:
Originally Posted by Big hammer View Post
Did you open the throttle wide open? That will make a difference. I still think/hope that more running will get the compression up!

Yes, WOT. Poured some Seafoam into the gas. Hopefully that helps. Will idle it and maybe try again today.


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Old 07-28-2020, 08:58 AM   #19
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Default 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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Old 07-28-2020, 10:32 AM   #20
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Default 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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Old 07-28-2020, 11:20 AM   #21
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Default Re: Compression Test Results

Lets try and get the engine properly before anything else.
The one cylinder is low, hopefully it might come up a bit when the engine has been run awhile.

The compression numbers aren't that bad for an older rebuild or original. Mine has had 45# since I bought in 1975. This engine was rebuilt in 1961. And not all compression gauges are created equal, there can be quite a variant between them.
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Old 07-31-2020, 07:00 PM   #22
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Default Re: Compression Test Results

Alright, update on the situation. I gave it a pretty thorough Seafoam treatment and that seemed to help a little. It wasn't missing driving it in second gear down my little road like it did earlier. I decided to take it for a drive around and it did about as well as it did when I drove it a few years back. I drove it for about 10-15 mins twice today.

Engine braking makes some little "pffts": https://youtu.be/dwF_Dt1UWac

Climbing up hills is slow going and gets smokey. I know I have a few significant exhaust leaks around the manifold and the manifold to muffler clamp area. https://youtu.be/vwEFWsOERJA

I mainly wanted to get the truck going well enough to give my mom a ride for her birthday. I have another engine that I'll look to put in over the winter when I have more time. This one is clearly on its last legs.

Thanks for the help everyone. It was fun to drive it again.
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Old 08-01-2020, 04:34 PM   #23
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Default Re: Compression Test Results

Good to hear. Your mom will love it.


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