Compression Test on my 318, not good

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MileHighDart

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Been wanting to do some tuning in my 318 to try and get it running better.
Going to do a dist recurve, get a wideband 02 gauge/sensor so I can get the carb dialed in better, etc.

But I thought I'd start with the basics and start with a compression test.

Keep in mind this 318 was built about 17 years ago, but has probably less than 3000 miles on it. Most of those years it has set waiting for a car to go into.
I have had some issues with it smoking after its warmed up. Changed the valve seals and that helped a little, but it still smokes a little after it warms up, but not too bad.
I'm starting to think that the rings are collapsed or stuck and I'm getting some oil past the rings, and this may also be why I got the numbers I did on my compression test.

Look at the attached pic for the results.
#1 was the lowest at 101, highest on a couple other cylinders was 128.

I've heard that you should have only a 10 percent variance between cylinders.
How should I proceed trying to fix this? Is there a solvent or something I can use to try to un-stick the rings, or do I need to tear it down, get new rings, give the cylinders a quick hone and reassemble ?
Or should I just run with it like it is for the summer, and fix it next winter?
 

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Next, do another compression test "wet" and see if it makes a difference.

A "wet" compression test will let you know if it is in the rings or valves. Take an oil squirt can and put 2-3 "squirts" of oil in each cylinder just before you do the compression test. See if there is any difference between the "wet" and "dry" tests (the dry test is without oil).

If you get better results after squirting the oil in than without, then you may have a ring/blow by issue.


After the wet and dry compression test, perform a leak down test if you have a leak down tester. This will also let you know if it is in the rings (leaking/hissing in the crank case), or intake valve (hiss/leaking sound through the intake/carb), or exhaust valve (hissing/leak through the tailpipe).

If it turns out to be a ring issue (which it may be with your initial results), then I would recommend installing new rings and possibly doing a quick hone with a "ball hone" when you do. You can get ball hones at NAPA.
 
If you do have to replace the rings, make sure that the new rings can spin freely by hand before installing the pistons in the block.

Also make sure that the ring gaps for the top two compression rings are at least 90° apart or more from each other. Do the same for the two thin oil rings, 90° apart or more from each other.
 
Your NOT going to hurt it running it the way it is! Unless you have lots of money to put into a new or rebuilt motor, just enjoy it for the summer!!!!!! I know I would!

Then start saving up and build a 360 for it over the summer or the coarse of a few years.
 
Just curious when you did the test was the engine warm? All of the plugs out? Carb blocked open? 3 to 5 revolutions per cylinder tested?
 
The "smoking" after it is warmed up is more concerning to me than the compression test results. That could be some massively worn valve guides. I bet your compression and smoking could be cured with rebuilt/new heads..... Just a guess though.... :) . Of course, this would be cheaper than a rebuild of the engine. I would take the heads off and see the condition. If its the heads, its an easy fix. If its not the heads, then they needed to be pulled to rebuild the motor anyways. Oh, by the way, replacing worn heads with leaky valves and valve guides with good heads will be an instant performance gain along with better gas mileage and no smoking! Or, of course, ignore it and drive it like it is.....
 
Let's get the data first and go from there.

No sense in spending more money than he has to by just throwing parts at it to fix it.

Take some data, evaluate it, then spend your time and money wisely on what will make a difference.
 
Heads / valve guides, etc should be fine.

When I built this engine 17 or so years ago it got the works, new guides, hardened seats.
Bored 030 over, new pistons, bearings, double roller timing set, cam, hi volume oil pump, etc.
Since its been mostly just sitting around all this time and only has 2-3 K miles on it I doubt I wore out the valve guides. I'm really thinking its a ring thing.
 
67Dart273 said:
You should do this warm
Click to expand...

I'll warm it up and redo the test and see what I get.

I just did it cold cause getting the two rear plugs on the drivers side out
are kind of a pain cause of the brake booster, and taking them out with the engine hot
could be a little hard on the hands.
 
MileHighDart said:
Heads / valve guides, etc should be fine.

When I built this engine 17 or so years ago it got the works, new guides, hardened seats.
Bored 030 over, new pistons, bearings, double roller timing set, cam, hi volume oil pump, etc.
Since its been mostly just sitting around all this time and only has 2-3 K miles on it I doubt I wore out the valve guides. I'm really thinking its a ring thing.
Click to expand...

As mentioned a comprression check should be done warm, throttle wide open and disconnect the coil + for any accurate readings!
 
If it runs good, leave it alone.
 
MileHighDart said:
I'll warm it up and redo the test and see what I get.

I just did it cold cause getting the two rear plugs on the drivers side out
are kind of a pain cause of the brake booster, and taking them out with the engine hot
could be a little hard on the hands.
Click to expand...

Warm the engine, then let it cool just to the point you can get the plugs out without burning yourself. Block the carb open as well.
 
Run it and enjoy it,, Do another compression test after you've put a few hundred miles on it..

If it's been sitting for a while,, the compression may come up after a few miles ..

hope it helps
 
if the engine only has 3000 miles on it on a rebuild, it probably isn't broke in yet.
I would change the oil and drive it.
 
First test, engine cold, numbers are as much as 21 percent different between cyls.

101 128
115 109
108 128
109 115




Next Test, engine hot (only burnt one finger getting the last plug out..lol) Some numbers went down, others came up. But they're much closer to all being the same only a 13 percent difference.

113 110
120 105
118 117
120 114


Last test, engine hot, couple squirts of oil in each cyl. All numbers came UP, now only a 10 percent difference.

120 124
125 113
122 120
125 120

The last set of numbers coming up tells me there might be a ring problem. Could be they are collapsed from so many years of sitting. Or, like some already mentioned, the engine might not even be broken in yet. 3000 miles on it is actually a high estimate, it's probably less.
 
krazykuda said:
Next, do another compression test "wet" and see if it makes a difference.

A "wet" compression test will let you know if it is in the rings or valves. Take an oil squirt can and put 2-3 "squirts" of oil in each cylinder just before you do the compression test. See if there is any difference between the "wet" and "dry" tests (the dry test is without oil).

If you get better results after squirting the oil in than without, then you may have a ring/blow by issue.


After the wet and dry compression test, perform a leak down test if you have a leak down tester. This will also let you know if it is in the rings (leaking/hissing in the crank case), or intake valve (hiss/leaking sound through the intake/carb), or exhaust valve (hissing/leak through the tailpipe).

If it turns out to be a ring issue (which it may be with your initial results), then I would recommend installing new rings and possibly doing a quick hone with a "ball hone) when you do. You can get ball hones at NAPA.
Click to expand...

karl just hit the nail on the head,do this test frist,also make sure the battery stays fully charged,low starter cranking speed will give false readings
 
MileHighDart said:
First test, engine cold, numbers are as much as 21 percent different between cyls.

101 128
115 109
108 128
109 115




Next Test, engine hot (only burnt one finger getting the last plug out..lol) Some numbers went down, others came up. But they're much closer to all being the same only a 13 percent difference.

113 110
120 105
118 117
120 114


Last test, engine hot, couple squirts of oil in each cyl. All numbers came UP, now only a 10 percent difference.

120 124
125 113
122 120
125 120

The last set of numbers coming up tells me there might be a ring problem. Could be they are collapsed from so many years of sitting. Or, like some already mentioned, the engine might not even be broken in yet. 3000 miles on it is actually a high estimate, it's probably less.
Click to expand...

add a jar of seafoam engine oil treatment in the oil and drive it for a few miles, drain oil refill and check compression, sounds like rings have never had chance to seat

wasn't sure before, sounded like high milage engine but you confirmed its not
 
MileHighDart said:
First test, engine cold, numbers are as much as 21 percent different between cyls.

101 128
115 109
108 128
109 115




Next Test, engine hot (only burnt one finger getting the last plug out..lol) Some numbers went down, others came up. But they're much closer to all being the same only a 13 percent difference.

113 110
120 105
118 117
120 114


Last test, engine hot, couple squirts of oil in each cyl. All numbers came UP, now only a 10 percent difference.

120 124
125 113
122 120
125 120

The last set of numbers coming up tells me there might be a ring problem. Could be they are collapsed from so many years of sitting. Or, like some already mentioned, the engine might not even be broken in yet. 3000 miles on it is actually a high estimate, it's probably less.
Click to expand...


Let's go with "not broken in yet".

Drive it around and put some more miles on it. Then do the wet and dry compression test again after a few months to see if it gets more stable. If not, you can always do the rings later or next winter.
 
did you run a compression test after installing the engine the first time to have a base line .also did you use stock pistons, a cams shaft with a large duration or wide lobe separation will lower the compression by 30 psi .I had one 318 I replaced just the cam in it and the first thing noticed was a lack of starter noise (wine) so went back and the compression was 150 before cam and 120 after cam swap.so what I'm getting at with the engine sitting that long it could take 1000 miles to reseat the rings there could be nothing wrong at all.
 
Sounds like another case of "not enough abuse" to keep it fresh LOL... First I'd change the oil to some CONVENTIONAL stuff then go out and really wail on it a few times, hit the gas at low speed to build cylinder pressure which will push the rings up against the cylinder walls harder and wear them into the surface.

If this were a 100,000-mile engine with a stock bottom end I'd say it was toast but in your case it should still be fine unless you did something wrong. Also you say 17 years and only 2-3k miles, I could definitely see your valve stem seals getting dried out from sitting that long.
 
krazykuda said:
Let's go with "not broken in yet".

Drive it around and put some more miles on it. Then do the wet and dry compression test again after a few months to see if it gets more stable. If not, you can always do the rings later or next winter.
Click to expand...

This ^^^^^^ you really need to listen to the voices of experience on this. They are telling you the right thing. Keep drivin it.
 
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