Tips on checking compression

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72Plymouth

72Plymouth

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Ok I'm slowly going through my 318 and checking things. Would it be good to do a compression check? Just want a better idea of the condition to see how long I can go before putting new parts or doing a complete rebuild.

I've never checked the compression on anything, but here are the steps I know of:

1) Unplug coil from distributor
2) put something in carb to keep the choke plate open
3) Remove one spark plug at a time and connect compression checker
4) crank engine for a few seconds for each one

I will be looking at my shop manual but just wanted to check if anyone had any good tips or guidance of what I should be looking for.

Thanks
 
1 is correct...or use a remote starter switch with the ignition key off
2...you want to pull the throttle blades fully open so the engine can inhale...lol
3...remove all spark plugs....so the engine can crank easy
4. as you spin the engine..you will see the gauge jump...with 3 spins you will have your max compression

5. what you are looking for is consist number from the cylinders...
 
unplug coil, pull all plugs, crank with carb WOT. crank till comp stabilizes.
then do again and spray a little oil in first
 
Warm up the engine first to get the oil flowing and everything up to temperature. This will make taking out the plugs less fun, but the rings will seal better and your bearings will thank you.

Pull all the spark plugs. The engine will spin faster, and the oil will stay on the rings longer (no compression in untested cylinders to push the oil past the rings)

Don't "put something in" the carburetor. You want to hold the throttle wide open, so the engine can pull all the air it needs. Brick on the pedal, wire the linkage open, whatever works best. You do not want to be letting the pedal up and pressing it back down after each cylinder, this will fill the engine full of fuel and wash all the oil out of the cylinders.

Crank each cylinder the same # of times. Usually max compression is reached by 3-4 compression strokes.

Be consistent. Always do your compression checks the same. That way, when you do one later, they're comparable. The speed that the engine spins makes a difference, so make sure your battery has a good charge. Getting a baseline for your engine is good, although it won't necessarily tell you "how long it will last". It is handy for diagnosing new problems though, and can give you a basic idea about how well things are sealing. A leak down test is more accurate for telling engine condition IMO, but a compression check is a good place to start.
 
70aarcuda said:
1 is correct...or use a remote starter switch with the ignition key off
2...you want to pull the throttle blades fully open so the engine can inhale...lol
3...remove all spark plugs....so the engine can crank easy
4. as you spin the engine..you will see the gauge jump...with 3 spins you will have your max compression

5. what you are looking for is consist number from the cylinders...
Click to expand...

Ohh got it. What's a good way to hold that open since it has spring tension? Just by hand?

Where would you connect the remote starter? Would the starter relay be the small rectangular box on the fender near the battery area?

Thanks
 
Engine oil should be fine, its to lube the cyl walls and help the rings seal. I never knew about holding the carb open. Im old and still learnin'!!
 
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