Terrible Problem w/ A-4 - Almost Ran Aground - Ideas?

[ViribusUnitis]

Something weird is going on in your compression test. Remember, a compression test isn't much of a absolute test. It's more reletive to how the other cylinders do.

IMHO, you've got 3 bad cylinders. All of the cylinders should be +/- 10 of each other. The highest is 25% or so more than the others. SOMETHING IS WRONG.

The next issue is with how large the readings are. According to the internet, the Atomic 4 has a 6.3 to 1 compression ratio. The atmosphere has an absoute pressure of 14.7 psi or so. 6.3 times atmospheric pressure is 92 psi. A pressure guage should show a maximum of 78 psi. (the diffrence between the pressure in the chamber, and the atomsphere) Since you've got one that shows 120, something is way wrong. Eighter you've got large carbon build ups that are raising the compression ratio, the compression ratio is higher than the 6.3 the internet says, or you did the test wrong. (miss read the pressure guage or something equaly strange.) I don't think the compression ratio is wrong, these are fairly low pressure engines.

Water in the 4th cylinder. Did you close the sea cock for the cooling system? As you turn the engine over to do the compression test, the coolent pump will continue to pump. However, with out the exauste gas to flush out the water from the wet exauste system, water can back up aginst the engine. It can like splash up over the anti-siphen stuff. From there it only needs to work it's way into the engine.

[mesquaukee]

Originally Posted by ViribusUnitis

. According to the internet, the Atomic 4 has a 6.3 to 1 compression ratio. The atmosphere has an absoute pressure of 14.7 psi or so. 6.3 times atmospheric pressure is 92 psi. A pressure guage should show a maximum of 78 psi. (the diffrence between the pressure in the chamber, and the atomsphere) Since you've got one that shows 120, something is way wrong..

The cylinders are hot. The cool air drawn in warms up from the heat of the cylinder walls. It also warms up from compression.
The old PV=nRT has a bite in it.
Did the calc making certain assumptions and it gave me a maximum pressure due to both sources of heating of 135 PSIA or 120 PSI Guage.

[ViribusUnitis]

Originally Posted by mesquaukee

The cylinders are hot. The cool air drawn in warms up from the heat of the cylinder walls. It also warms up from compression.
The old PV=nRT has a bite in it.
Did the calc making certain assumptions and it gave me a maximum pressure due to both sources of heating of 135 PSIA or 120 PSI Guage.

That still doesn't make much sence.

Using your numbers, and I'm not convinced that your getting that much heat up, 120 should be max with everything perfect. I sure as heck havn't experenced that with old auto engines. There should be SOME leakage. If 120 is perfect, he's got 1 perfect cylinder? On a 20 year old engine? That doesn't pass the smell test.

I guess it could be right, but...

What I'm trying to say is that the test looks poor to me. I think there was a problem with the methoidology. Then again...

[svquest2]

Originally Posted by CruiserHopeful

"how could so much water fill up in that one cylinder so fast? the only way it would fill up SO FAST is if there was a GIANT hole somewhere, not a tiny little leak in a gasket "

That's also my point of concern

Joe S

[mesquaukee]

The assumptions I was making were;
1.-there was a lot of water in the cylinder that meandered down through the rings and made a perfect seal, an oily, tary, water emulsion.
2. -the same happened with the valves making a perfect seal.
3. -water was left in the cylinder #4 taking up space, it was “splashed” out

I know it is bizarre. It is the only reasonable explanation based on the currently supplied data.
We need the wet and dry compression tests.

It would be a good question on a mechanics licensing exam.

[mesquaukee]

Long distance diagnostics sucks! Reminds me of snailmail.
Maybe we need webcams.

[CruiserHopeful]

alright - went back for round 2 of compression tests today. 3 total were done.

1) warm engine up for 20 minutes
2) close thru-hull while still running for 30 additional seconds to clear water out of system
3) compression test 1

results:
1 - 91
2 - 92
3 - 93
4 - 92

4) put plugs back in and run at higher RPMs for 5 minutes so the engine is hotter than it was before by a few degrees
5) compression test 2

results:
1 - 95
2 - 94
3 - 96
4 - 95

6) do a "wet" compression test. Fill the cap of the oil container about 1/2 way and pour 10w30 engine oil into each cylinder prior to testing

results of "wet" compression test:
1 - 105
2 - 103
3 - 106
4 - 105

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So that's that. Still getting oil burning out the exhaust, and still getting oil burning out of the oil fill cap when I rev it up above idle. Was unable to replicate the "engine dying" problem except for ONCE yesterday during the initial compression test. It is very sporadic when it decides to kill itself when in idle, but I have a couple theories about that.... hear me out:

Theory 1)
The piston rings are all somewhat bad on all cylinders. this allows oil to come up into the detonation chamber and burn with the gasoline. At low RPM's this is not a problem because there is enough gas to keep the engine running. At high RPM's - more oil gets into the cylinder, thus robbing ignition power from the gas and air, causing it to stop igniting and stop running.

(by the way, the engine starts right back up after it dies)

Theory 2)
The blue smoke is oil getting burned, but that is not what is causing the engine to die: those are 2 separate problems. The engine is dying because it is losing fuel supply (possible junk in the gas tank, floaters or whatever that plug the fuel hose and block all fuel from entering the tank.. killing the engine. Once it dies, suction is released from the fuel line and the floater is "released", and the engine will start right back up)

----------------------------

ARGHHHHHHHHHHHHHHHH

[svquest2]

You seem to be forgetting about the possible plugged fuel vent. Try running the engine with the fill cap removed.

Joe S

[CruiserHopeful]

Originally Posted by svquest2

You seem to be forgetting about the possible plugged fuel vent. Try running the engine with the fill cap removed.

Joe S

opened it up for a second, didnt notice any vacuum or anything. Smoke still occurs - but engine didnt die. Again, its sporadic, I cant seem to replicate it unless I am out motoring around under load, thats the ONLY time it happens consistently

[mesquaukee]

Based on the wet and dry tests your rings are as near perfect as one can expect. All within a few PSI of each other with a 10% difference between wet and dry.
Blue smoke coming out of the exhaust if the rings are good indicates worn intake valve guides. At idle speeds there is a lot of vacuum in the intake manifold and cylinder. This sucks in oil around the guides. Blue smoke is the result.
The problem is the exhaust gasses coming out of the oil filler. If the rings are good that leaves the exhaust valve guides. A quick and messy way to find out is to take the valve or rocker cover off and run the engine. Some oil will be thrown around by the rockers. Look very carefully and you will see exhaust coming up from the oil drain holes or it will be coming out of the valve guides.
You also might want to check to see if you have a restriction in the exhaust creating excessive back pressure.
Worn valve guides are indicative of poor oil flow to the head.
Best of luck.

[CruiserHopeful]

Originally Posted by mesquaukee

Based on the wet and dry tests your rings are as near perfect as one can expect. All within a few PSI of each other with a 10% difference between wet and dry.
Blue smoke coming out of the exhaust if the rings are good indicates worn intake valve guides. At idle speeds there is a lot of vacuum in the intake manifold and cylinder. This sucks in oil around the guides. Blue smoke is the result.
The problem is the exhaust gasses coming out of the oil filler. If the rings are good that leaves the exhaust valve guides. A quick and messy way to find out is to take the valve or rocker cover off and run the engine. Some oil will be thrown around by the rockers. Look very carefully and you will see exhaust coming up from the oil drain holes or it will be coming out of the valve guides.
You also might want to check to see if you have a restriction in the exhaust creating excessive back pressure.
Worn valve guides are indicative of poor oil flow to the head.
Best of luck.

I like where your head's at. Theres only one small issue with this particular engine - I need to take of the carb/fuel pump in order to get at the valves to ANY degree, and once I get at them, I wont be able to run the engine to look for the splashing. :/

[Ex-Calif]

You have to solve the sump blowby. If the compression test is good and it looks good then the only other way to pressurize the sump is past the exhaust valve guides.

This suggests a restriction in the exhaust system, as could the water in the #4 cylinder. Although when not running the raw water pump could be floading the exhaust system.

[mesquaukee]

From what I understand an Atomic 4 is a flathead engine with the valves in the block.
The valve tappet cover is behind the carburetor and flame arrestor. That does create a problem for easy access.

The question is how much work do you want to do. If you want to do as much as possible yourself and are mechanically inclined go for it. You will learn a lot.

It can only be the valve guides letting exhaust into the crankcase. For so much to leak there has to be a restriction in the exhaust to create so much back pressure. It could be why the engine stalls at high speed under load. Check all of the exhaust system first. Disassemble and visually check all of it. If there is a shutoff valve in the exhaust make sure it is fully open.
If all of that is clear the valve guides must be severely worn out. That only happens from poor lubrication.
If you want to check that you would need to remove the valve cover. You should be able to reattach the carburetor to the engine and run it. It would answer the question of where the exhaust gasses are coming from.

If it is the valve guides they and the valves can be replaced with the engine in the boat if there is room to work. It is tedious to do but doable if you are mechanically inclined and have the time.

Good luck.

[Ex-Calif]

I would be leery of running the engine with the valve cover off.

If the guides are suspected and I was pulling the valve cover off I would get a spring compressor and check for wobble.

First check is the exhaust system - easier and worthwhile at this point.

[sww914]

Any engine run for 30 minutes without cooling is fried.
Something in there was terribly overheated and isn't working right anymore. Your rings are damaged, the cylinders are probably out of round and scored, and most engines would have a warped head as well. I'm not 100% on what happens to the head on a flathead, I work on modern cars daily, not boat, tractor, or forklift engines so I don't see any flatheads.
At any rate it was badly overheated and now it won't run right. That's very bad. Even if the compresion isn't too bad right now the rings have probably lost their temper and they will get worse soon. Even if by some miracle you get it to run well temporarily you won't ever be able to depend on it fully after this. Any compression test results semantics don't really count for too much with me, your 2 main symptoms are
1- it was badly overheated.
2- it doesn't run right anymore.