Compression Testing Old 302 questions
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New User
Joined: Mar 2021
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Compression Testing Old 302 questions
Hi Guys,
First post, I picked up a 1977 F-100 302 to replace my 76 F-250 Camper Special That ran on Propane. I pulled the carb off to rebuild/learn about it and in the mean time I want to run a compression test to see if I even want to rebuild the carb and to see the actual condition of the cylinders as it's been sitting for about 12 years,
So just a few questions this being my first time:
Is it fine that the carb is off? will I run into any issues?
Do I pull out one plug at a time to test or all at once?
Do I have to unplug the ,main lead from the distributor?
I don't know if the tank has any gas, and if it does will there be something shooting it out?
If it sounds like I don't really know what i'm talking about it's because I don't, I'm a really a cook but I love these trucks more than any 4 wheeled vehicle on or off the road and want to eventually know everything and be an expert but i'm getting tired of looking up information and getting half answers or straight up wrong ones. I trust people here before anything that pops up in google.
Thanks in advance!
First post, I picked up a 1977 F-100 302 to replace my 76 F-250 Camper Special That ran on Propane. I pulled the carb off to rebuild/learn about it and in the mean time I want to run a compression test to see if I even want to rebuild the carb and to see the actual condition of the cylinders as it's been sitting for about 12 years,
So just a few questions this being my first time:
Is it fine that the carb is off? will I run into any issues?
Do I pull out one plug at a time to test or all at once?
Do I have to unplug the ,main lead from the distributor?
I don't know if the tank has any gas, and if it does will there be something shooting it out?
If it sounds like I don't really know what i'm talking about it's because I don't, I'm a really a cook but I love these trucks more than any 4 wheeled vehicle on or off the road and want to eventually know everything and be an expert but i'm getting tired of looking up information and getting half answers or straight up wrong ones. I trust people here before anything that pops up in google.
Thanks in advance!
Grumpy goat
Joined: May 2017
Posts: 3,059
Likes: 597
Hi Guys,
First post, I picked up a 1977 F-100 302 to replace my 76 F-250 Camper Special That ran on Propane. I pulled the carb off to rebuild/learn about it and in the mean time I want to run a compression test to see if I even want to rebuild the carb and to see the actual condition of the cylinders as it's been sitting for about 12 years,
So just a few questions this being my first time:
Is it fine that the carb is off? will I run into any issues?
Do I pull out one plug at a time to test or all at once?
Do I have to unplug the ,main lead from the distributor?
I don't know if the tank has any gas, and if it does will there be something shooting it out?
If it sounds like I don't really know what i'm talking about it's because I don't, I'm a really a cook but I love these trucks more than any 4 wheeled vehicle on or off the road and want to eventually know everything and be an expert but i'm getting tired of looking up information and getting half answers or straight up wrong ones. I trust people here before anything that pops up in google.
Thanks in advance!
First post, I picked up a 1977 F-100 302 to replace my 76 F-250 Camper Special That ran on Propane. I pulled the carb off to rebuild/learn about it and in the mean time I want to run a compression test to see if I even want to rebuild the carb and to see the actual condition of the cylinders as it's been sitting for about 12 years,
So just a few questions this being my first time:
Is it fine that the carb is off? will I run into any issues?
Do I pull out one plug at a time to test or all at once?
Do I have to unplug the ,main lead from the distributor?
I don't know if the tank has any gas, and if it does will there be something shooting it out?
If it sounds like I don't really know what i'm talking about it's because I don't, I'm a really a cook but I love these trucks more than any 4 wheeled vehicle on or off the road and want to eventually know everything and be an expert but i'm getting tired of looking up information and getting half answers or straight up wrong ones. I trust people here before anything that pops up in google.
Thanks in advance!
You should tie the choke plate in the open position, or pull the carburetor. If you have an intake valve that's leaking or stuck open, you can still get a compression reading if the carburetor's choke horn is closed. Opening the choke plate, or removing the carburetor will eliminate the chance of false reading.
Pull all the plugs so the engine turns over easily. That ensures consistent testing on all cylinders.
Since there are no spark plugs, it doesn't matter, but I disconnect the coil wire from the distributor, if I haven't removed the distributor.
If you remove the carburetor, then you need to either plug the fuel line, or disconnect the line between the tank and pump.
Good luck. Let us know what your compression numbers are.
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New User
Joined: Mar 2021
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Ok I’m gonna remove the tape covering the air inlet. Carb throttle and choke are off so it’s gonna get air.
find and plug gas line
remove All plugs at once
setup battery
start doing one cylinder at a time cranking to get the highest reading (3-4 cranks)
and just make sure there isn’t a huge variation in numbers right?
Am am I missing anything?
oh oh if I don’t disconnect the main spot on the distributor will all those wires be snapping shocks when I’m cranking? And can that cause a problem? Or no?
find and plug gas line
remove All plugs at once
setup battery
start doing one cylinder at a time cranking to get the highest reading (3-4 cranks)
and just make sure there isn’t a huge variation in numbers right?
Am am I missing anything?
oh oh if I don’t disconnect the main spot on the distributor will all those wires be snapping shocks when I’m cranking? And can that cause a problem? Or no?
Logistics Pro
Joined: Oct 2006
Posts: 4,031
Likes: 891
From: East Central Ia
If it's been setting for 12 years hook fuel line to hose and let it pump it out into a can and see what you have in the tank. Probably not good.
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8th Gear
Joined: Nov 2020
Posts: 8
Likes: 0
Ok I’m gonna remove the tape covering the air inlet. Carb throttle and choke are off so it’s gonna get air.
find and plug gas line
remove All plugs at once
setup battery
start doing one cylinder at a time cranking to get the highest reading (3-4 cranks)
and just make sure there isn’t a huge variation in numbers right?
Am am I missing anything?
oh oh if I don’t disconnect the main spot on the distributor will all those wires be snapping shocks when I’m cranking? And can that cause a problem? Or no?
find and plug gas line
remove All plugs at once
setup battery
start doing one cylinder at a time cranking to get the highest reading (3-4 cranks)
and just make sure there isn’t a huge variation in numbers right?
Am am I missing anything?
oh oh if I don’t disconnect the main spot on the distributor will all those wires be snapping shocks when I’m cranking? And can that cause a problem? Or no?
Yes, they'll be sparking unless you disconnect the distributor wire from the coil.
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