Lead down test, could use some help interpreting results

[Lumpy Grits]

Champion was OEM for all of AMC.
LG

 

[tarry99]

I did my first "leak" down test today (misspelling on the title, and I can't figure out how to change it). I used the 'stick something in the spark plug hole' method to find TDC. I think twice I missed it, but I repeated those cylinders. Based on my results, I think I've got problems. But I wanted to see if anyone could find a flaw in my process.

Equipment, OTC leak down tester that has two gauges, both in PSI. Pancake air compressor. I started at cylinder 1. That one I didn't follow instructions on (instructions on tester said to equalize left hand gauge at 90, I did 100 based on a YouTube video). I did that for cylinder 2 as well, I think. I followed the firing order listed on my intake manifold (1843572). After round 1, I started the motor to make sure I didn't screw anything up. then I did two more cylinders (3 and 2) once more. And as I sit and write this down, I see I missed cylinder 6. Damnit. Either way, here are my results for each:

Cylinder 1: Left gauge (LG) 100 (no notes after equalized), Right gauge (RG) 19
Cylinder 8: LG 100, RG 16
Cyl 4: LG 90 -->81 (after equalized), RG 14
Cyl 3: LG 90-->84, RG 15 (initial test tail pipe hiss, but I think I missed TDC)
Cyl 3, round 2: LG 90-->80, RG 43 (oil filler cap was blowing some smoke)
Cyl 5: LG 90-->85, RG 14 (a little hiss from carb, but again, might have missed TDC).
Cyl 7: LG 90-->80, RG 14 (tail pipe)
Cyl 2: LG 90-->72, RG 12 (carb hissed, I rotated motor until it stopped hissing, thinking I missed TDC again).
Cyl 2, round 2: LG 90-->78, RG 62, (oil filler cap hissing).

So, if my understanding is correct, if I missed TDC, I might hear hissing from carb or exhaust. But I shouldn't hear anything from the oil filler cap, even if I missed TDC, right? No bubbles in radiator.

I think I've got bad rings in cylinders 2 and 3. Maybe some valve problems in 5 and 7. But, I suspect those issues are more attributed to my noob status than engine problems.

Thoughts? I also took photos of my spark plugs for each cylinder, but can't figure out how to download them just right now. I saw a lot of carbon deposits on 3, and 2 looked light brown on the ceramic part.

Sorry for this mess of data. It's in a spreadsheet on my computer, but I don't know how to paste it. Anyway, am I looking at a rebuild? Or did jack my methods up so bad that I need to do it again? Thanks.

Jeff

jpcobe is online now Report Post

First off it's doubtful you could ever get accurate readings from an air source such as a Pancake compressor that has such a small tank for volume........ When you set the gauge and start pumping up the cylinder the volume needs to remain constant and exceed the leak for a period of time in order to be able to read the percentage of leak.
The best way I have found to find TDC without the valve covers off is to crank the motor over slowly ( no spark plugs in any hole)......via either a remote starter button or using a breaker bar on the crankshaft............put your thumb or finger in the test hole on the outside edge to block any escaping pressure. As the motor is turned over the pressure created inside the cylinder on the compression stroke will try to blow your finger off of the opening.... stop right there .....whether or not your before TDC or slightly after will not make any difference...........as both valves will be closed and the piston will be near TDC.........leakage heard at the carb........could indicate bad intake valves, Leakage at the exhaust could be exhaust valves and leakage at the crankcase breather could spill rings........what your really looking for is a gauge to understand how much leakage is occurring within the motor.......10-20% is pretty normal when warm...........50% is time for an overhaul.

 

[jpcobe]

Pics of my intake if I can get them to load. Anything telling in these?

 

[jpcobe]

Another from other side

Spark plug number RN14YC.

 

[Lumpy Grits]

That's the correct SP.
LG

 

[Turbogus]

Did you address the PCV yet jp?

 

[jpcobe]

Been working, and getting home late, and kids practice etc etc...gonna look at that this weekend if it's nice. And hopefully do a compression test. Have a vacuum gauge coming next Tuesday. I'll let ya'll know what I find. Thanks for asking.

 

[jpcobe]

Tarry99: question: so if a pancake compressor can't hold 90 psi for a test, why can't I just keep it lower? Can I just put, say 50 psi in and let it read from that baseline? What am I missing here? I'm sure it's obvious...but I'm missing it. I appreciate these explanations...I don't know anyone local to help me out.

 

[jpcobe]

PCV has sludge in it. Normal? It does rattle so I don't believe it's stuck. Thoughts on this?

 

[Lumpy Grits]

Clean it with carb or brake cleaner.
Have you ck'd ALL intake & exhaust manifold bolts to be sure they are TIGHT?
Run the psi at what it should be run.
LG

 

[jpcobe]

More to follow on bolts for intake/exhaust. No I didn't think about that one.

Compression test results, methodology.
1. Engine warm.
2. Removed wire to ignition coil
3. Started at cylinder 1 and went back forth 2,3,4 through 8 (so didn't miss any this time!).
4. I took a drive between 7 and 8 to charge the battery. I realize that might have skewed some results for later cylinders.
5. Cylinder 1, first try, I didn't hold throttle down, so I retested after 8, and that's the result I've listed below.

Results in PSI:
1-125
2-114
3-120
4-119
5-120
6-117
7-121
8-112

Once again, did I jack up the test, or are these results reliable? And what do they mean? Thanks again.

I'll clean the PCV per instructions.

A couple of notes. When I pulled oil filler cap off after warming/driving the motor, it was tilted again (as though it was being pushed off) and smoke was coming out the top (similar to what it looks like when steam comes off a cup of coffee...maybe it was steam?)

 

[jpcobe]

Well, I did miss a step. I removed each spark plug and tested each cylinder one by one. I reviewed some instructions and see ALL plugs should be out for this test. What does this error do to the results? Learning curve is a bit steep for me apparently...

 

[Lumpy Grits]

Was the throttle open on the carb when taking all the readings?
Closed throttle will give you low compression readings.
YES- pull all of the plugs first.
You only have 13psi diff. across the board. That's very good!
LG

 

[jpcobe]

Throttle open for all--I was pushing the gas pedal to the floor. Is that the same as at the carb? Do I need to redo? I saw some say the way I did isn't ideal, but also didn't say it would invalidate results. I was satisfied with how close they were too, but they seemed low to me.

 

[jpcobe]

Re: Leak down test, could use some help interpreting results

Okay, did the compression test again, this time with another vehicle connected with jumper cables, running, to keep the battery charged for all cycles. I also opened the throttle at the carb with a bungee cable. I did NOT remove all spark plugs on this one due to time constraints and concerns with labeling and getting the right wires/plugs back to the right cylinders. I also ran a vacuum test. I couldn't find a reference in my FSM or the Chilton's, that told me which hose was the manifold vacuum. I'm certain its there, but 35 degrees outside, I wasn't finding it. I used the PCV hose in the rear of the carb. I removed PCV (also to squirt some carb cleaner and hit it with a wire brush) and connected the PCV side of the hose to the tester. Is this the wrong place? Overall results seem good:

Cylinders
1-142
3-AMC 150
5-146
7-146
2-147
4-148* moved battery cable to get out of the way of my wrench.
6-144
8-171/161* repositioned battery cables, not enough juice, repositioned again and hit the throttle on booster vehicle. Engine much faster, got very high readings.

Vacuum. 21 in. (or maybe it was 19, I didn't write it down, but it was well within the acceptable range listed on my tester instructions).

So, I guess I don't understand what I'm missing. I expect I may have done the vacuum test wrong. I'll dig into the manuals more today. But if I did it right, then vacuum looks good, and engine compression looks good (even if I didn't remove all the plugs). What other reasons might I be getting for continued leaks and oil filler cap blow-off? Much of the emissions stuff has been removed, I'm running long tube fenderwell headers, so air injection stuff is gone. EGR is there, but no hoses hooked up.

Any other thoughts on this? If it's nice next weekend, I'll try and do the leak down test once more, with a warm engine and I'll study up on finding TDC with the gauge (is that on the harmonic balancer I think?) instead of the 'pencil' method used last time.

I also looked at my choke, and the cable wasn't moving it. I tightened it up, but it didn't return to original position, so I think a spring is broken inside or something. I think I'll just order a new choke and see if that gets that piece fixed.

 

[Turbogus]

Quote: I also looked at my choke, and the cable wasn't moving it. I tightened it up, but it didn't return to original position, so I think a spring is broken inside or something. I think I'll just order a new choke and see if that gets that piece fixed.

If that's a Carter carburator lurking uder your air cleaner the choke may not be kaput, just mal-adjusted. Rotating the black plastic choke housing clockwise will put less tension on the spring, thus making for greater choke delay or more choke as it were.

 

[jpcobe]

I have the MC2100. I've got a similar looking item on it, I'll see if that might do the trick. Thanks for the suggestion.

 

[Posi]

Vacuum. 21 in. (or maybe it was 19, I didn't write it down, but it was well within the acceptable range listed on my tester instructions).

Most importantly was the needle moving between 19" and 20" or was it a steady reading? If you have vac brakes remove the line at the intake and get your readings there.
The engine should be warm, and all plugs pulled. The engine will turn over faster with less strain on your battery, and you won't be sucking fuel down.
Fully charge your battery, (buy new if it doesn't take a charge), remove the plugs, then redo the compression test on a warm engine. Testing procedures have to be consistent with all cylinders.
It sounds like your readings will be fine, but I would redo as mentioned to be positive.

 

[Lumpy Grits]

Posi has it 'rite'.
Keep the charger on the battery while you're do'n the test.
LG

 

[jpcobe]

Needle not moving, stayed pegged. I kept the battery hooked up to the other vehicle via jumper cables, and kept the other vehicle running to keep the charge going. I stayed as consistent as possible without removing all plugs. I read somewhere that, though not recommended, it was an acceptable method. BUT, all the feedback here says take out ALL plugs, and that's the next approach I'll take when I've got some more time. I'll have to get set up to mark my wires and lay my plugs out without interruption. I'll do that next time.

Thanks, again. Like I said the learning for me is a bit steep. I do something, sit down and check my results against my methods, ask some questions here, visit the FSM and Chilton's, YouTube a bit, and learn something more. I do appreciate the feedback, even if it might seem repetitive.