Running Rough, version 2 - Stuck valve? Blown head gasket?

[hank]

Our A4 is intermittently running rough and has no power at cylinders 3 & 4. Several weeks ago, after an hour of motoring, she suddenly lost power. I found the boots on spark plug wires at #3 and #4 were melted/charred. When I replaced the wires she ran fine.

She ran ok the next 5 or 6 outings, but felt like she was maybe 90% and needed some fine tuning. One time she ran rough when I started her, as if missing 3 and 4 again, but smoothed out after a minute. On our last outing, as I backed down hard at the dock, she slipped out of reverse and revved up for a second or two.

Last night, she started right up, but ran rough, and wouldn't smooth out. She also has a new noise. At idle she was quiet, but when I gave her a bit of gas, I’d hear a pretty loud tapping noise from the rear of the engine, and if I gave her a bit more gas – say above 1200 rpm, the tapping noise would lessen and be more consistent.

I’ve gone through the ignition system – new parts, adjustments, plenty of spark. I’ve been through the fuel system, and all seems fine there.

Based on what I’ve found in the forum –( and I’ve found lots of info which helped me get this far – thanks everyone!!), I’m guessing I have stuck valves (at 3 and 4 ?!) , or a blown head gasket between 3 and 4?

I plan to measure compression tonight and see if the valves move through the spark plug holes, and add a few drops of MM oil. I’d appreciate your thoughts and advice. Next steps?

Thanks.

Hank

[Don Moyer]

Hank,

Please go ahead and complete the compression check and get back to us. The clicking sound could be an indication of a broken valve spring or two (perhaps on cylinders 3 and 4).

Don

[hank]

Cylinder 4's compression is a big fat 0

Thanks Don.

I took the compression readings as follows:
#1=91, #2=96, #3=90, #4=0.
The rear most valve on cylinder 4 is stuck open.

A search of some images, discussions etc helped clarify that would be the exhaust valve, and that the intake valves are next to each other and share a common manifold port. Given that cylinder 3 has good compression, would this shared intake port explain the lack of power at #3? Would the sticky #4 exhaust valve explain the molten plug wires many weeks ago at both cylinders 3 & 4?

Next would be to attempt and push the valve down with the bent screwdriver or allen wrench. If I'm successful and #4 compression comes back and the clatter goes away, then consider myself lucky (for now) and maintain a regimen of Marvel Mystery oil?

If not... off with her head (I couldn't resist), alt, manifold, valve cover and inspect/replace broken spring/retainer/keepers?

Thanks again!

Hank

[sastanley]

Hank, Going along with Don's suggestions (he is the master afterall), I would only comment that you can be more generous than a 'few drops' of MMO...I think Don refers to 'a few squirts' in his instructions. But, an MMO treatment can affect your pressure readings, so I would do the compression test with the motor 'as-is', then begin the troubleshooting process to determine the problems.

[Don Moyer]

Hank,

I think you're on the right track to pursue freeing up of the exhaust valve
in the fourth cylinder and hope that continued use of Marvel Mystery Oil
(MMO) will keep it free.

I don't believe the fact that two cylinders are sharing a common intake port
is causing any problems in your engine. As long as both intake valves
sharing a common intake port are working normally, they act as one-way check
valves which prevent anything bad that may be going on in either cylinder
from backing up and affecting the other.

However, given your report of the third cylinder also losing power in the
recent past, I do have some concern that you're getting a bit of water
damage from somewhere (frequently from something going on in the exhaust
system). If you're fortunate enough to get the last exhaust valve to break
free, I recommend keeping the raw water through-hull valve closed at all
times that the engine is not running to see if the plug in the fourth
cylinder stays clean.

Don

[hank]

purring like a kitten!

Don, sstanley - thanks for the input. Good news. I went to the boat at midday, put a squirt of carb cleaner down the valve stem, and was able to reach the valve with an allen wrench and tap it down, then turn over the motor. After repeating 3 or 4 times, the valve seemed to be seating and moving well. I checked compression, and cylinder 4 was now at 90 pounds! I put a couple of squirts of MMO by the valves and started her up, but... she still ran rough, with no power at cylinders 3 or 4. Spark plugs in cylinder 3 and 4 are wet w/ gas, I checked spark at the plugs and it was strong, and I have good compression.... hmmm... I let it run about 15 minutes, then had to run back to work.

After work, I went back and verified one more time that everything ignition-wise was right. I started her up again, and .... she ran perfect! Wow! I guess the MMO worked its magic.

I let her run for an hour. Before I left, I took compression readings again, 89-88-89-89, added another 4 squirts of MMO and ran her for 2 minutes and called it a night.

So, it looks like I'm back in business. Thanks again for the help y'all, and all of the folks who have posted their stories that I was able to study.

Don, I agree with your concerns about moisture in cylinder 4, and probably cylinder 3 too. I'll close the water intake seacock as you suggested when not running the motor. This is my first experience with a water cooled exhaust, so I have a question. The boat is a 29' Ericson, with a factory exhaust arrangement that looks to be in excellent shape from the outside. It's 'water muffler'? is higher than the engine, so if it is failing on the inside would it result in water back to the cylinders? If so, how would I check this? Are there other things I should check? When I ran it for an hour today, it stayed right at 140 degrees, though it usually runs 160.

Thanks again for all of the help.

Hank

[rigspelt]

Don, I agree with your concerns about moisture in cylinder 4, and probably cylinder 3 too. I'll close the water intake seacock as you suggested when not running the motor. This is my first experience with a water cooled exhaust, so I have a question. The boat is a 29' Ericson, with a factory exhaust arrangement that looks to be in excellent shape from the outside. It's 'water muffler'? is higher than the engine, so if it is failing on the inside would it result in water back to the cylinders? If so, how would I check this? Are there other things I should check? When I ran it for an hour today, it stayed right at 140 degrees, though it usually runs 160.

I'm an A4 newbie, but in the past few weeks I've been reading up on exhausts to redesign the exhaust in our boat. The old exhaust is on the garage floor and needs replacing.

While you're waiting for Don's wiser and more authoritative suggestions, consider checking the cooling water line running from the aft end of the manifold to the dry stack. Does it enter the dry stack at a point where it looks like cooling water could run backward in the dry stack to the manifold and hence to the aft valves? I'm no expert, but my reading suggests the cooling water should inject at least 4" below the top of the dry stack.

If there is an antisiphon valve at the top of a loop in that hose, is it working properly? I'm not yet clear on why a dysfunctional antisiphon valve there would cause water to get into the cylinders, but my current understanding (I could need correction) is that if a siphon gets going, then water flows from the raw water intake through the water pump (if impeller allows this flow) and into the waterlift muffler. That floods the waterlift muffler, allowing back flow into the manifold again through the dry stack.

In a well designed and functioning exhaust, the hose from the waterlift muffler to the transom carries mixed warm gasses and cooling water. Since there is more gas than water, the volume of the water in that mix is low. (If I got my high school math right, the volume of a foot of 1.5" ID hose is only 0.1 US Gallons or 0.35 Liters if pure liquid). The muffler can overflow most commonly in two ways, as I understand it: 1. By overcranking an engine that does not start. 2. Or, on shutdown, what cooling water there is in the standing part of the hose falls back into the muffler, but should not be able to flow back into the manifold unless for some reason the muffler overfills and the water finds a way to run backwards.

Some exhaust references I found:

http://www.abycinc.org/committees/P-01.pdf

http://www.moyermarine.com/faq/1.2.html

http://www.boatus.com/goodoldboat/Marine_exhaust.asp

http://www.yachtsurvey.com/exhaust_risers.htm

http://www.yanmarhelp.com/i_exhaust.htm (diesel, but principles similar).

http://www.moyermarine.com/forums/showthread.php?t=2772

http://www.moyermarine.com/forums/showthread.php?t=2317

[rigspelt]

Good news. I went to the boat at midday, put a squirt of carb cleaner down the valve stem, and was able to reach the valve with an allen wrench and tap it down...

Stupid newbie question: were you able to do that through the spark plug hole with a flashlight?

[sastanley]

newbie response to newbie question

rigspelt...

My experience has been that the spark plug holes are closer to the valves than they are to the pistons...when I pull the plugs out I can see a valve..usually my #2 cylinder has the most light shining on it. Not sure which valve yet, but I can see something in there...sometimes it is open, sometimes closed.

I think that this is the reason that Don suggests squirting MMO away from the monfold, so that it also does some work to the rings as well and not just rolling down the valves.

[Don Moyer]

Most water lift mufflers have a drain on the bottom. If you have such a drain, you can configure a small valve and hose barb to which you can attach a small diameter clear plastic tubing running vertically upward to serve as a monometer. To check the static level that your exhausting engine cooling water reaches within your exhaust system (the piezometric level), simply open the valve and note the level that the water inside the muffler reaches immediately after engine shutdown.

In your system, the water level will no doubt normally remain inside the vertical dimension of the water lift muffler itself. On boats with smaller mufflers, the piezometric level inside the exhaust system sometimes reaches a short distance up into the hot section in the direction of the manifold. In any case, there should be plenty of hot section above this piezometric water level to prevent engine cooling water from backing up into the manifold and into the engine while heeling when sailing in your worst case sea conditions.

One more point about your system. I would suspect that any breakdown within the internal baffling of your muffler in the future would result in a significantly higher piezometric water level than the level you would be noting now immediately after shutdown when the muffler is presumably working normally.

Don

[hank]

rigspelt,

Thanks for the exhaustive research (pun intended). I hadn't found much yet, this will really help .

Re the allen wrench - of course all that I know about an atomic 4 I learned from this site. I found a picture of a headless block and the underside of the head that kelley had posted. (kelley is right - a picture is worth a thousand words - thanks!)

http://www.moyermarine.com/forums/showthread.php?p=9989#post9989

The spark plug hole is more or less between the exhaust and intake valves, but offset a bit to the center of the head - towards the piston. I couldn't see the exhaust valve. I slipped the short end of a small diameter (maybe 1/8 or 3/32) into the sparkplug hole between the valves, and rotated it over on top of the exhaust valve. Then I lightly tapped on the top of the allen wrench.

Oh - a funny thing happened - I was holding the allen wrench with my fingers and I dropped it... into the head . Luckily, I was able to extract it with needle nose pliers. I locked my needle nose vice grips on it before any additional tapping...

Hope that helps.

Hank

[hank]

monometer

Thanks Don.

I've searched a bit but have been unable to find a drawing of this exhaust system, so I drew this. The red line is the monometer.

Unfortunately, my muffler does not have a drain plug, so adding the monometer would be prohibitive. Understanding the design of the system would help me, does this look about right?

Thanks again.

Hank

[Don Moyer]

Hank,

You have the correct concept.

Don

[rigspelt]

There's a marmalade word I haven't heard before:
piezometer: 1. An instrument for measuring fluid pressure, such as the pressure of water or gas in a pipe.

[rigspelt]

I've searched a bit but have been unable to find a drawing of this exhaust system, so I drew this ... Understanding the design of the system would help me, does this look about right?

Looks like the cooling water enters the muffler separately from the hot exhaust gasses, rather than entering the dry stack to cool the gasses prior to entering the muffler? That's an interesting design I have not yet encountered in my limited learning about boat exhaust systems. Can you post a photo of the waterlift muffler in relation to the manifold?