Engine Sputtering Under Load- Help with Understanding Test Results

[Moabrubi]

Hi All,

Just recently my engine started sputtering pretty bad under load. I started with the basics, but my findings have led to towards the internals of the engine. Some background:

1.Engine idles smooth, at 19 In of vacuum. When revved the engine begins to spit and sputter and has limited power.
2.Full tune-up has been done including installing a new distributor with all tune up related items dialed in.
3.At idle, I get a puff from the exhaust every few seconds. When I hold a dollar bill up to the exhaust pipe, it sucks it back and flutters the dollar bill back and forth, leading me to believe an issue with the exhaust valve.
4.I did a valve adjustment, and upon adjustment discovered the #4 valve had 0 clearance and was completely, I adjusted it to .014 afterwards.

So that led me towards a compression and leak down test where I would like some assistance in narrowing down exactly what I am looking at.

Compression Test, Done on a warm engine at WOT.

Dry:
Cylinder 1:85
Cylinder 2:60
Cylinder 3:68
Cylinder 4:50

Wet:
Cylinder 1:91
Cylinder 2:65
Cylinder 3:85
Cylinder 4:60

Cylinder Leak down test, Admittedly I was having some issues determining where TDC was. When I set #1 at the TDC mark on the flywheel, i was getting leakage into cylinder #2 on the test. I spun the engine around and was finally able to get an appropriate reading, not sure what I was doing wrong.

The method I ended up using was simply sticking my finger over each cylinder and stopped rotating the engine when air finished coming out. Below are my results.

Cylinder 1: 12PSI loss
Cylinder 2: 58PSI loss, I can feel air coming out of cylinder 4 and the exhaust when I do this one? Not sure if I was doing something wrong but I tried a few times and got the same result.
Cylinder 3: 40PSI loss, I am getting bubbling out of the radiator and also leakage out of the exhaust
Cylinder 4: 58PSI loss, I can feel air coming out of the exhaust.


My guess as to what is going on, bad exhaust valves on 2,3 and 4 and a bad head gasket? Sorry for the long winded post, I just wanted to give you guys all the data that I had. Let me know if you think I messed up on any of the testing.

Thank you!

[dpcd67]

Very thorough test, although I would have thought it would not produce a steady 19 inches on a vacuum gauge. Did it flutter? The gauge I have would indicate leaking valves.
I rely on vacuum gauge for everything.

[Moabrubi]

Very thorough test, although I would have thought it would not produce a steady 19 inches on a vacuum gauge. Did it flutter? The gauge I have would indicate leaking valves.
I rely on vacuum gauge for everything.

It was fluttering quite a bit before I adjusted that #4 valve that was closed shut. Afterwards, the needle is pretty steady.

Here is a litle video I took showing the vacuum after I adjusted it, along with the sputter. FYI, I was pointing to the engine RPM, which was about 610 and you can hear the idle “puff” as well.

https://youtube.com/shorts/ZSoDeQ-za1c?feature=share

[JAB]

I'm assuming that it ran poorly for a while, and then suddenly became undriveable? 19 seems high considering the condition of the other parts, but yes, it seems you're looking at pulling the head to verify what your test results seem to indicate. It will be interesting to hear what you actually find. I hope it's a head gasket, and not a crack, and I hope the valves and seats are easily taken care of. The increase from dry to wet might indicate the rings are as nearly worn as the valves were. If this is a timing chain engine it's probably stretched too. Lot's of assumptions on my end, but these things don't wear out in just one area, it all kinda goes together.

You posted the video after I replied, so I just watched it now. Nice jeep.

[Moabrubi]

I'm assuming that it ran poorly for a while, and then suddenly became undriveable? 19 seems high considering the condition of the other parts, but yes, it seems you're looking at pulling the head to verify what your test results seem to indicate. It will be interesting to hear what you actually find. I hope it's a head gasket, and not a crack, and I hope the valves and seats are easily taken care of. The increase from dry to wet might indicate the rings are as nearly worn as the valves were. If this is a timing chain engine it's probably stretched too. Lot's of assumptions on my end, but these things don't wear out in just one area, it all kinda goes together.

It hasn’t been running too bad, I have noticed a loss in power over the years, but it’s still been perfectly drivable. One day it just started doing the sputtering thing and it all went downhill from there. Just as a side note this rebuilt GPW motor only has 3700 miles

Im a little stumped at how well it idles and the vacuum I am getting. It doesn’t seem to mesh with the results I’m getting. It sounds like I need to pull the head but to be honest I’m not really sure what I’m looking for once I pull it.

[dpcd67]

Rebuilt, as in, rebuilt to absolute new condition, or just overhauled, which means something else. Only 3700 miles on a truly rebuilt engine would not be expected.
That is the same vacuum gauge that I have. And I saw the needle jump.

[Moabrubi]

Rebuilt, as in, rebuilt to absolute new condition, or just overhauled, which means something else. Only 3700 miles on a truly rebuilt engine would not be expected.
That is the same vacuum gauge that I have. And I saw the needle jump.

Unfortunately, don't have that data, I received it already built. I presumed completely overhauled.

It does have the very slight fluctuation, but I thought that was normal.

[Scoutpilot]

Please elaborate on the "new distributor".

[Wolfman]

One thing that jumped out at me early in your post.
You said the engine performance was slowly getting worse but the latest issue happened all of a sudden.
The engine idles pretty well but when you speed the engine up is when it really runs worse.
When you adjusted the valves, did you take a close look at the valve springs ?
A broken spring will do what you and I just described.
The springs usually break on the end in contact with the engine block so at a glance, it isn't that obvious.
I never use old springs on a rebuild.

[Adam]

When and if you pull the head, first I would look for a ridge in the cyl walls, then try to move the piston side by side in the cyl bore. if there is a ridge at the top, well engine probably not rebuilt, if pistons move side to side,, well its done. You should still be able to see the honing crosshatch marks on the walls at that low mileage. Look at the head gasket for carbon trails from 1 cyl to another, before you take the gasket all the way off

compression is terrible, if you pull a valve, look to see how deformed the tappet adjusters are, a good rebuild would of replaced them or cut them flat. look at the valve seat area on the valves, is there a groove cut into the valve at the contact point with the seat? can you see machineing marks on the head and deck surfaces? or just pitting and holes and debri in the water jacket passages.

Adam

[dpcd67]

Yes, all those things they said.
If a vacuum needle is pulsating any at all, that is indicative of something bad. If you had increased the RPM, that needle would have gone crazy.
As for "completely overhauled", there is no such thing; I always use the US Army terms here, and with everything.
Rebuild: A major component of the end item (COEI), which has been brought back to new, original factory specifications in every way.
Overhaul: To repair an item to some lower specification, specified by whomever is directing the work and issuing the contract. The Scope of Work (SOW), will be in the contract.
So, I think your engine might have been overhauled, but not rebuilt. Meaning it was not in new condition when you got it. Otherwise it would not have deteriorated so fast. This is common in the old vehicle community. Previous owner slaps new rings in it and maybe shims up the bearings; Presto! I rebuilt it! Yeah, no.

[Moabrubi]

Please elaborate on the "new distributor".

Hi Rick

Freshly rebuilt distributor. I want to say my Dad had it rebuilt my Willys Distributors, it was supposed to be for another Jeep build.

One thing that jumped out at me early in your post.
You said the engine performance was slowly getting worse but the latest issue happened all of a sudden.
The engine idles pretty well but when you speed the engine up is when it really runs worse.
When you adjusted the valves, did you take a close look at the valve springs ?
A broken spring will do what you and I just described.
The springs usually break on the end in contact with the engine block so at a glance, it isn't that obvious.
I never use old springs on a rebuild.

I did my best to try and look at the springs, but I need to take some time to pull the fender and manifold to get a better look. From what I can see with everything assembled, the springs seem to look OK.

Could broken valve springs cause the compression loss across all cylinders as I am seeing?

When and if you pull the head, first I would look for a ridge in the cyl walls, then try to move the piston side by side in the cyl bore. if there is a ridge at the top, well engine probably not rebuilt, if pistons move side to side,, well its done. You should still be able to see the honing crosshatch marks on the walls at that low mileage. Look at the head gasket for carbon trails from 1 cyl to another, before you take the gasket all the way off

compression is terrible, if you pull a valve, look to see how deformed the tappet adjusters are, a good rebuild would of replaced them or cut them flat. look at the valve seat area on the valves, is there a groove cut into the valve at the contact point with the seat? can you see machineing marks on the head and deck surfaces? or just pitting and holes and debri in the water jacket passages.

Adam

Thanks, it looks like I'm pretty committed to pulling the head at this point, so at least I kind of know what to look for, I'm sure I will end up posting lots of pics when the time comes and asking for feedback.

Yes, all those things they said.
If a vacuum needle is pulsating any at all, that is indicative of something bad. If you had increased the RPM, that needle would have gone crazy.
As for "completely overhauled", there is no such thing; I always use the US Army terms here, and with everything.
Rebuild: A major component of the end item (COEI), which has been brought back to new, original factory specifications in every way.
Overhaul: To repair an item to some lower specification, specified by whomever is directing the work and issuing the contract. The Scope of Work (SOW), will be in the contract.
So, I think your engine might have been overhauled, but not rebuilt. Meaning it was not in new condition when you got it. Otherwise it would not have deteriorated so fast. This is common in the old vehicle community. Previous owner slaps new rings in it and maybe shims up the bearings; Presto! I rebuilt it! Yeah, no.

Gotcha, well if I have to go through the headache of pulling this thing and sending it off, I'm just going to drop the coin and have it done right. I do have a feeling it was just overhauled; I did a compression test a few years ago and the numbers were less than stellar then and it only appears to have rapidly deteriorated.

[dinof]

It appears that the shop that did the rebuild, overhaul, or whatever, did a lousy
job. 3700 miles is way to little for all these issues going on in this motor.

[Wolfman]

I went back and looked at the results of your compression test.
All cylinders are really low. Dry & wet. Are you sure how accurate your compression gauge is ??
Number 3 cyl. showed the most improvement wet. That would be piston rings.
All cylinders showed some improvement but not a lot more than I would expect with the wet test. More likely valves.
What did you use for the leak down test ?? A pressure differential gauge or some other method.
With the pressure differential gauge, the 2 gauge set is connected to each cylinder, set to TDC on the compression stroke. Set the inlet pressure on the gauge set, connected to an air compressor, to 80 PSI and read the outlet pressure on a second gauge that is connected to the cylinder. ( I am using an aircraft gauge set )
The lower the second gauge reading, the more leakage the cylinder has.
If the second gauge reading is really low, you can hear where the leaking air is going. Into the crankcase ( listen to the oil filler tube ), out the carb or out the exhaust ( leaking valve ). If you have a blown head gasket, you would get air out another spark plug hole. 1 & 2 or 3 & 4 since these cylinders are next to each other and really close. You can also watch for bubbles in the radiator. Head gasket and/or a cracked head or block.
A broken spring can be hard to see in the engine. The spring coil usually breaks in the close coils at the top and is not always that easy to see in the engine that is in the jeep.
Weak springs are another problem. Springs have a free length. If they measure short, out of the engine, the spring has collapsed and is weak. Does not hold the valve closed as tightly as it should and slows the valves action. Prevents the valve from closing as fast as it should, especially at higher engine RPM. Of course, a broken spring really screws up the valve action and closed pressure on the seat.
Another problem. Bent springs. If you set all the springs on a table together, they should all be standing straight and the same height. That should be the free spring length. Not sure what that is off the top of my head.
Hope I answered your questions and gave you an idea what to look for.

[YLG80]

Rebuilt, as in, rebuilt to absolute new condition, or just overhauled, which means something else. Only 3700 miles on a truly rebuilt engine would not be expected.
That is the same vacuum gauge that I have. And I saw the needle jump.

Unfortunately, don't have that data, I received it already built. I presumed completely overhauled.

It does have the very slight fluctuation, but I thought that was normal.

dpcd67 is right. Here you can see how a stable needle looks like
https://youtu.be/DukvdYbzyKs
I took that video today while slightly readjusting my engine timing.(too much advance)

But I love your engine sound while revved. It's like a WWII aircraft. Unfortunately it's not an aircraft engine ...

Yves