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Old 05-07-2009, 10:06   #1
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Terrible Problem w/ A-4 - Almost Ran Aground - Ideas?

Atomic Four 4-cylinder... 1980'ish I think
Its in a sailboat, and rated at 30HP I believe

OK let me preface this by saying that about a month ago I ran the engine for about 10 minutes without the thru-hull for my coolant (salt water cooled), my mistake I know, but it started burning oil like crazy

This time I went out and it was going good (dont know the RPM, but reasonable speed and going ~5knots. We did this for about 2 hours then all of a sudden the engine begins lugging and dropping RPM's. Like im lowering the throttle, but I'm not. It did this once every 10 minutes at the beginning, and then did it every minute or so. After about 30 minutes of this the engine just died. We were dead in the water - so threw it into neutral - turned it over, and hoped for the best.

It started back up, and runs just fine when in neutral (no load might have something to do with it) - can throttle it through the entire range and it sounds normal - but as soon as I put it into drive it acts up.

1) it will run just fine if I leave it at the LOWEST throttle setting, but we're going 0.8 knots
2) once I bring up the RPM's even a little bit, oil smoke starts pouring out of the oil fill cap, and the engine kills itlself in a couple minutes of run time (under load)
3) the temperature of the engine is fine, took temp measurements at different points all around the thing, highest was about 200 degrees
4) water is coming out of my exaust (originally thought it was an overheating issue, but im starting to re-think that)


should I go out and just buy a new engine? Or do you think it can be salvaged?
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Old 05-07-2009, 10:31   #2
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I belive your rings are toast.

The "smoke" out of the oil fiell cap is your dead give away. It would seem that as you throtal up, the combustion gases flow down past the rings and then out the oil fill cap.

I'd probably start by pulling the plugs and seeing if they're oily. (If the rings can't keep the combuston gas in the chamber, they can't keep the oil out.) Then a compression test, and probably leakdown test.

At the very least you probably need to rebuild the engine and replace the rings. If you've got time, you can probably fix that yourself. In the process of destorying the rings you might have also scratched the cylinder walls. If the cylinder walls are scrached up, the engine is probably junk.

The dieing under load is troublesome, and points to any number of a host of other issues. Everything from burnt bearings, to excessive oil on the plugs.
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Old 05-07-2009, 11:17   #3
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Yes cooked rings. Overheating causes the rings to stick in the grooves in the piston. As more and more exhaust gas passes by the rings the lubricating oil partially burns forming a tar which glues the rings in the grooves in the depressed position.

If you have very few hours on the engine the rings can be replaced. The cylinder walls are honed to remove any glazing and to create a cross hatch pattern. This can be done with a power drill and a simple device. This cross hatch pattern acts as a hone to “grind” the new rings down a little to form a precise fit. That is one of the reasons why during the break-in process you go slow under a light load. You do not want to gunk up the rings with hot bypass gasses.

If you have a lot of hours you will have to have the cylinders bored out. This is due to the wearing of the cylinder. There will be a sizeable ridge at each end of the stroke where the rings stop and reverse direction. It cannot be honed out. New oversized pistons and rings need to be installed as the old piston will clatter around in the larger space creating all sorts of problems.
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Old 05-07-2009, 13:28   #4
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I agree with the posts above but believe you should have it checked out by someone who knows the engine before you do anything. I have had several including one rated at 25 HP back in 1940. They have been around a long time and are reasonably reliable if you don't abuse them. They are not the best marine engine however, because they have no intermediate bearings on the crankshaft. That means that excessive loads or rpm's can cause some warpage of the crank.

There are lots of parts available and lots of shops that work on them. There are many rebuilds and even some new A-4 engines around. I rep;aced the last saltwater cooled A-4 I had, after lots of hours and a broken exhaust spring, with a fresh water cooled A-4 that I bought used. Someone bought my old one and fixed the exhaust spring, and they both went away running just fine.

If you're a mind to it, you can replace in with a diesel which is a direct replacement, but they are expensive and some people don't like a diesel smell (I'm not one of them though).

Anyway check it out and good luck.

Joe S
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Old 05-07-2009, 14:02   #5
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Check to be sure there's nothing wrapped around the prop/shaft, and that the transmission has oil.
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Old 05-07-2009, 14:35   #6
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I think all that exhaust coming out of the oil fill cap when the engine is loaded gives the culprit away. Stuck piston rings.

There is supported by the history of running the engine without any cooling water. I presume that the engine is directly cooled by sea water due to the statement “salt water cooled”, there is no heat exchanger. I would imagine there are a lot of hours on the engine as it did not seize (engine has a lot of play due to wear).
This also damaged to some degree the vanes in the raw water pump even though it still appears to be pumping some water.
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Old 05-07-2009, 19:39   #7
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Definitely time for a rebuild.

A compression check will verify the rings are shot.
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Old 06-07-2009, 04:55   #8
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If you overheated it enough to toast the rings, then it's likely you've got other problems too -- warped head or block, bearings, scored bores, etc.

It's a very simple engine, so if you've got time you can pull it apart yourself. You can easily check the bores yourself with a micrometer and by feel. You can rebuild the whole thing without too much trouble -- block and head should be capable of being milled flat by a machine shop unless the warpage is extreme; you can usually have the crank ground for oversized bearings. If your bores are shot, you can have them honed or overbored, and put in oversize pistons. The valves will want grinding and new guides in any case. Since the machine shop will do all of the tricky stuff, you don't have to be a mechanical genius to rebuild your engine, and afterwards it will be good as new and ready for another 30 years of use.

If you can afford it, repowering with a diesel -- as someone said, there are direct drop-in replacements available, see: http://www.betamarinenw.com/Applicat...tomicfour.html --
will give you big benefits in much lower fuel consumption, much more durable and reliable, much less dangerous fuel to handle. Personally, I like diesels -- I like the way they sound, and I like everything else about them, which just feels right for marine use, in my subjective opinion. But you would not want to do this if you don't love your boat and plan to keep her for a long while, because you will never recover the cost when you resell her.
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Old 06-07-2009, 16:25   #9
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Alright, thanks for all the replies, really gave me a good idea on what to do for this. Here are the results of the compression test today:

(Cylinders are 1-4 going Fore->Aft)
Warmed the engine up to operating temp for 20 minutes
Took off all the plugs, and disconnected the gas line
Cyl 1 - 92 psi
Cyl 2 - 96 psi
Cyl 3 - 91 psi
Cyl 4 - 120 psi
So everything turned up OK I think (above 80ish is good as far as I know)

Another thing I noticed is that while I was testing cylinders 1-3, cylinder 4 started having water in in that was literally splashing all out of the empty spark plug hole [[I left the through-hull open for the coolant, so for some reason I believe that since there was no pressure pushing the exhaust water / air out (cooling water and exhaust gases are mixed directly in the exhaust manifold on the engine itself, and only one single 3 inch hose comes off the engine and goes into the muffler)... that water was simply pouring in from the exhaust valves inside the cylinder... so I dont think it is an issue!!! Ran it afterwards and it cleared the water out as far as I could tell after a minute of running. AGREE? DISAGREE?]]]

So theres that...

but then the same issue happened AGAIN. It cut off even not under load!
Im starting to think theres like a floater in the fuel system like the tank or something that plugs the fuel line as the gas sloshes around, killing the fuel feed.

Maybe a hole in the fuel hose? sucking air bubbles into the engine? It is VERY intermittent when it happens - seemingly at random.


OTHER PROBLEM
oil is still burning out of the oil fill cap... even though I took the temp all over the engine and NO hotspots showed up...


Can I add one more thing? I have a 20 or 15 gallon fuel tank on the boat, and all I can put into it is about 6 gallons worth of fuel, then it starts filling all the way up to the fill point and shoots gas all over the place... what gives?? could it be related to my original problem somehow?

phew.... thanks for reading
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Old 06-07-2009, 18:12   #10
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a4 engine

did you do a wet and a dry compression test? A wet test is to check for worn rings and the dry is for leaking valves. Judging from the compression readings it could be the valves. The readings should be within a few pounds of each other. As far as the fuel filling problem check your vent line for spider or wasp nest. If the tank isn't vented fuel will puke out the filler neck
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Old 06-07-2009, 18:22   #11
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did you do a wet and a dry compression test? A wet test is to check for worn rings and the dry is for leaking valves. Judging from the compression readings it could be the valves. The readings should be within a few pounds of each other. As far as the fuel filling problem check your vent line for spider or wasp nest. If the tank isn't vented fuel will puke out the filler neck
Im not sure what the difference is between the two... which one DID i do, and what do I need to change to do the other style?
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Old 06-07-2009, 19:31   #12
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A wet and dry test are both a test for rings. It is an integrity test, the oil that is squirted in is to seal the rings, all other leaks such as valves remains constant.
The process is 1) Take dry readings. 2) Squirt in some oil to wet the rings 3) test again.

The wet and dry readings should be within 5-10% of each other. If it is 20-25% or more the rings are shot regardless of the actual values. All cylinders should be within 15% of each other for each test. There is a big difference with what is happening to the rings while running at speed compared to a compression test. The rings may be a little “sticky”,

As you can see from the values the wet cylinder. #4 wet with water, had a much higher compression 120 to 91-96. The rings in #4 only sealed with water, not as effective as oil, was more than 25% of the other dry cylinders. This indicates there is a problem with the rings no matter how you want to interpret the results.

An engine blowing a lot of exhaust out of the oil filler can only come from two places, rings or exhaust valve guides. Worn exhaust valve guides would not rob the engine of power except if the engine room was poorly ventilated and the exhaust was recirculated through the engine. The power loss from bad rings is self evident.
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Old 06-07-2009, 19:39   #13
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I may be stating the obvious but water in the cylinders is not a good thing. Pressurization of the oil sump system is also not a good thing.

Normally the compression test is done with the piston at or near top center. I don't know what procedure you used to do the compression test. i.e. hooked up a guage and cranked the engine over is what it sounds like.

A differential pressure test may be more telling. This uses 2 gauges and a reference pressure, usually 80PSI. The first guage is set to 80 and then the air goes through a fixed orifice. The second guage is read to determine pressure drop. 80 over 70 or 80/70 or better is a good target. A differential test has the advantage of being able to move the piston up and down (a wrench on the crank pully nut) in the cylinder to see if there are any changes in the first inch or so of piston travel.

If you were doing a cranking test the water you saw coming from cylinder 4s spark plug hole could be backing up from the exhaust system. I would disassemble and inspect the exhaust for a restriction. This would definitely give you problems.

However the excessive blow by is still not explained. If the exhaust system is backed up there is a chance that the back pressure is escaping to the sump system via the exhaust valve stems. This clearance is tight but but not sealed.
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Old 06-07-2009, 19:41   #14
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I agree about the plugged tank vent and that will cause a vacuum on your fuel system and cause a loss of power and engine stalling.

I am puzzled about your water in the cylinder however. I believe that the exhaust side and the cooling side of your exhaust manifold are isolated from one another. The water should have an exit port at the end of the manifold, and mix with the exhaust on the exit or downhill side of the exhaust mixing elbow,-- so you would have to fill the exhaust line from the low point beyond the mixing elbow all the way back over the mixing elbow to get water to the exhaust valve.

If your mixing elbow happened to be above the anti-siphon elbow or loop in the exhaust, then the water would never back up into the exhaust valve.

Take a look at that again. Good compression or not, you may have a leak in the head gasket.

Joe S
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Old 06-07-2009, 19:54   #15
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I agree about the plugged tank vent and that will cause a vacuum on your fuel system and cause a loss of power and engine stalling.

I am puzzled about your water in the cylinder however. I believe that the exhaust side and the cooling side of your exhaust manifold are isolated from one another. The water should have an exit port at the end of the manifold, and mix with the exhaust on the exit or downhill side of the exhaust mixing elbow,-- so you would have to fill the exhaust line from the low point beyond the mixing elbow all the way back over the mixing elbow to get water to the exhaust valve.

If your mixing elbow happened to be above the anti-siphon elbow or loop in the exhaust, then the water would never back up into the exhaust valve.

Take a look at that again. Good compression or not, you may have a leak in the head gasket.

Joe S
I agree with you about the exhaust, but my only issue with that is this:
"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 - hence my theory about exhaust water simply pouring back into the cylinder from the exhaust valves"
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