Compression test setup..
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Posting Guru
Joined: Mar 2001
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Compression test setup..
I bought a compression gage and hose today. I've been wondering what kind of condition my 300-6 in my '79 F100 is in. The directions indicate to: "disconnect the ignition's electricity at the distributer, ignition coil, or the distributer cap. The distributer's high tension lead should be grounded if it is diconnected." What does this mean? I assume I should remove the clip on the coil, but what about this grounding and is there anything special I should do to the ignition box? I just don't want to ZAP anything incedently. It also mentions to open up the throttle plates all the way. What's a good compression reading on a 300-6 with X80K miles on it?
Elder User
Joined: Mar 2001
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From: SF Bay area
Compression test setup..
[font size="1" color="#FF0000"]LAST EDITED ON 14-Jun-01 AT 10:40 PM (EST)[/font][p]Hi, if you have a hand-held remote starter tool, just clip one wire to the small terminal on the solenoid, and the other to the starter cable, then you dont need to disconnect anything. The instructions say that about disconnecting things because most guys would use the key to do this test. As for the compression reading, I would think of the 150lb ballpark (give or take) if it is running well. Most parts places should sell these remote starter tools if you don't have one.
Wayne
e-mail
http://home.pacbell.net/whomrig
Wayne
http://home.pacbell.net/whomrig
Senior User
Joined: Jan 2000
Posts: 238
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Compression test setup..
You are thinking of disconnecting the coil + and - wires, they mean high tension, which means the high voltage wire going to the distributor. If you dont ground it and use the key, it will spark everywhere, if its not close enough to metal to spark ive heard its not good for the coil. So if you go that route, just hook it to a bolt or something so its grounded out.
Dave
http://www.davesmonsterpit.com/dmp31.gif
Dave
http://www.davesmonsterpit.com/dmp31.gif
Lead Driver
Joined: Nov 2000
Posts: 6,620
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From: Albuquerque
Compression test setup..
It's a good idea to remove "all" the plugs while doing the test. In conjuction with proping the throttle open it gives the most accurate readings.
1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything
1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything
Moderator
Joined: Jan 2001
Posts: 56,951
Likes: 2,718
From: Virginia
Compression test setup..
Yes, the engine will crank too slowly with the plugs in to give an accurate reading. I would warm the engine too and make sure you have a good battery. Propping the throttle open gives the cylinders plenty of air to suck in and compress to give you a good reading.
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Compression test setup..
I bought a remote starter to add to my arsenal of tools..now how to use it. I'm getting different information. The first post stated to connect one clip to the small post (which one?) and the other to the engine starter post. The directions that came with the remote starter state to connect one side to the battery and the other to the "energized terminal on the solenoid." There's two small posts between the battery side and starter side. I assume these close the loop between the bat and starter via the ignition switch. So, what's the proper setup? I don't want to fry my solenoid or blow a fuse. Which of the two small posts is the energized one (the closest to the bat or starter)? Any experienced help is greatly appreciated. Happy Senior Ford Father's Day to those of you that have earned it 
Elder User
Joined: Mar 2001
Posts: 898
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From: SF Bay area
Compression test setup..
Hi, connect the starter to the small post closest to the big terminal and the big terminal (starter cable). This will be used in place of jumping the solenoid with a screwdriver.
e-mail me if you need to.
Wayne
e-mail
http://home.pacbell.net/whomrig
e-mail me if you need to.
Wayne
http://home.pacbell.net/whomrig
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Posting Guru
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Compression test setup..
The working connection ended up being one clip on the (+) bat and the other on the small post closest to the battery. Anyways, now to interpret the data. I did everything as I was supposed to do except remove the air cleaner off the carb. My lowest reading was 160 psi and the highest was 180 psi. The average was 168. The difference appears good as well as the average value for my '79 300-6, right? It did take about five successive strokes in order to get the highest reading (on each). This indicates worn rings, right? If I had any cracks in the head or block would the compression test indicate it?
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Moderator
Joined: Jan 2001
Posts: 56,951
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From: Virginia
Compression test setup..
Sounds good to me. You have to judge what the compression guage is telling you with how the truck runs and it's overall condition. I would say you have good compression though.
Cargo Master
Joined: Jul 2000
Posts: 2,281
Likes: 18
From: Northern California
Compression test setup..
I'd consider that to be very good. I like to watch the guage on the first stroke and see if it's making good comression on the first one but with 160~180 it sounds healthy.
Are you actually having a problem with the engine or are you just checking things out?
Are you actually having a problem with the engine or are you just checking things out?
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Posting Guru
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Compression test setup..
I'm just it out. I haven't had any engine problems at all. I bought the truck about a year and a half ago and I'm finally getting to the engine. Other than the fact that I have a number of gaskets and oil seals to change, the engine appears to be in good shape.