Shake shake shake....

[JOHN COOKSON]

# 3 has no spark or the spark is arriving to the cylinder at the wrong time.
# 4 has stuck valve (most likely) or a blown head gasket.

Are 3 & 4 spark plug wires interchanged to the wrong plugs?
Is there tracking inside the distributor cap between 3 & 4 terminals?
Did you look at the wiring while the engine was running at night to see if electricity escaping outside the spark plug wire(s)? (Post # 3).

There is a chance that if you can get the engine running on three cylinders the (alleged) stuck valve will shake loose.

ex TRUE GRIT

[sastanley]

# 3 has no spark or the spark is arriving to the cylinder at the wrong time.
# 4 has stuck valve (most likely) or a blown head gasket.

Are 3 & 4 spark plug wires interchanged to the wrong plugs?
Is there tracking inside the distributor cap between 3 & 4 terminals?
Did you look at the wiring while the engine was running at night to see if electricity escaping outside the spark plug wire(s)? (Post # 3).

There is a chance that if you can get the engine running on three cylinders the (alleged) stuck valve will shake loose.

ex TRUE GRIT

Excellent post. My engine with stuck #4 valve did this without removing the head. Gotta get #3 firing and it will not run too bad.

[Mo]

Stuck number 4 valve is common. I've seen many. Agree with John's interpretation so here's my 2 cents.

OK, Number 4 probably isn't going to come loose on it's own. 0 compression means it is stuck or might even be broken...more than likely just stuck. Question is WHY. So open your lazerttes, get some light down there, and have a look back along your exhaust. What you are looking for is that your exhaust rise off the manifold is higher than exit port of the boat. You also need to ensure the hose that goes from the exhaust manifold is on the downside off that high point..so that water is ejected down and astern.

Many, many #4 valve issues are from water coming back from the exhaust. Have you worked on your exhaust? I've seen a few #4 problems in the past few years that were owner caused because they replaced the hot exhaust without going high enough...subsequently, water dribbled back and after sitting a while seized valves. So my thought is if 4 seizes often because of inadequate drainage...more common than we think.

Next, how did the plugs look? Number 3 and 4 particularly. If they were really clean, instead of carboned up you have some water wandering in there. If they look really clean it's water washed.,,,I mean cleaned right off. If using NGK XR4 plugs they will look tanned and so will the porcelain part (that would be normal). If the plugs are the normally recommended plugs they should show more carbon buildup on 3 and 4 than those of 1 and 2...that would be normal.

In the past week I freed up 2 valves on different vessels using acetone and tranny fluid. The owners did the work so it's no different here. In my little oil dispenser I mixed 100 ml of acetone and 30 ml of tranny fluid and loaned my little dispenser to both guys. It is a very thin concoction. (NOTE try to direct it at the valve and not the cyliners. when directed at non seized cylinders it does drop compression a bit because is clears away the oil. ALSO NOTE" It is imperative to do an oil change after using acetone.

..they squired the concoction in around the valves for 3 days straight...both vessels were relieved of the valve issue. One has to change his hot exhaust...the other exhaust looked fine but he didn't spray anything in the top end last fall...so it stuck. It can happen. FYI, I lube my top end good each fall and turn it over once a month..no issues.

Now, that all said, last year it didn't work on a totally different boat...the reason was the valve was broken and part of it was just floating. Had to take the head off, side plate off and replace valve. That whole thing was cause by improper exhaust...fixed the engine, fixed he exhaust, no issues since. He had been having valve issue since changing his exhaust the year before.

So as John has indicated, looks like you have a fire issue on 3...might even be a bad plug, on 3, and 4 is likely a valve....just a matter of how much of a SOG it's going to be.

Remember, if you use acetone you change oil once you get it working. When all is said and done I think you will have it up and running. Don't maybe that exhaust though OK...it has to be right.

Edit:
Once you have sorted out #3 cylinder and fire it up (after soaking the valves) run for about 30 seconds at low idle and see if it evens out. If it doesn't even out squirt the #4 again and try it next day. If it does even out, do another compression check on 4 and see what you have. As soon as you know you have decent compression of 80 or so change your oil right away. Once that is done fire it up and idle it for a while keeping an eye on temp etc....then check compression again. Usually after a few minutes it will be fine. Note that if acetone got down around the rings you might see a little blue smoke for a little bit until the rings are re-lubricated....should be just a puff or two or someone might say "she blowing blue"...don't panic on that it will go away. Another though, not to overwhelm you, is maybe a pinhole in the manilfold....I'll just put that out there, but I've run into a few " rockers" that had a manilfold trying to put the fire out. (that doesn't sound like your issue but when it comes time to find a water incursion site...well)

Have a good night guys...spent 11 hrs on my boat today, worked like a dog on stuff I didn't need to be doing....aurgh.

All the best.

[JOHN COOKSON]

To tee off what Mo said........

Is there a siphon break in the exhaust somewhere? If there is it may not be working properly and allowing water to siphon from the exhaust into the engine.

ex TRUE GRIT

Edit: Switch #3 plug with #1 or #2 plug and see what happens. Does the problem follow the plug?

[DDO]

Thanks for the great info above and for following along. MMO was in overnight and today I inspected in the EI distributor and did a little maintenance in there. All looked so good. I am preceeding along with various tests, much of items above. Today the engine started up easy with a roar, and throttled up smoothly, and even most of the clickety stopped, but not the shaking. Pulling off the third spark plug did make a change now, not as strongly as when I pull the front or second. But - still 0 compression aft. Re exhaust system: design is good, hot section still looks like new, but flange and that area of manifold are "rusty". I was planning on working on that issue this year. (Last year was the water jacket side plate and etc.)

[scratchee]

You might want to read through my thread from when I had a very similar problem about six months ago (summary: fixed with lubricants and patience):

https://www.moyermarineforum.com/forums/showthread.php?t=11680

[sastanley]

DDO..I do not expect it to pop loose anytime soon. I religiously put in MMO every time I ran it..sometime in the middle of the summer it suddenly ran better and I had compression in #4. Let's hope yours is a little sooner!

[DDO]

I'm back.... No, cylinder #3 is not firing up although it has compression. Two hot spark plugs and two cold spark plugs made me look it over again, and lifting off the (new) plug wire didn't give the engine pause. So, I'll let the stuck exhaust valve on #4 (aftmost) wait while I try to get #3 working. Suggestions?

[ronstory]

Did you replace both the cap and rotor? I've ran into a bad brand-new cap/rotor combo once, and another where a new cap with an old rotor didn't work reliably.

I can't seem tell from the thread if you tested the wired and swizzled them around to eliminate the wires as the culprit.

[DDO]

I placed new plug wires, plugs, rotor, cap, and opened up the distributor to inspect & oil springs etc in there. Today I think I'll put the old plate with the traditional points back in in place of the EI, just in case that helps. I'm running out of ideas...

[Mo]

OK what does the plug look like. Is it clean. The only other reason I can think of a misfire, with a clean plugs, is a hole in the exhaust manifold. I had that problem 14 years ago. What I did was turn off the raw water intake valve and have someone standby to open it. Cleaned all the plugs, then started the engine let it run for 30 seconds or so...mine ran perfect...had my buddy open the valve and she started to rattle. Steam was trying to put the fire out in the top end of mine, both 3 and 4. It's an easy check.

[JOHN COOKSON]

Today I think I'll put the old plate with the traditional points back in in place of the EI, just in case that helps..

IMO this is a good idea.

ex TRUE GRIT

[scratchee]

I've found this tool to be very handy. You put it inline between a spark plug and that plug's wire, and there will be a visible spark inside the tool to confirm that your spark plug is is getting fired (but whether it's actually sparking or not depends on the proper gap etc).

It's called an inline spark tester. Amazon has several for less than $10:

[DDO]

I went to the auto store and bought the spark plug tester, very nice, a tidy way to test. Each of the 4 plugs made the same flashing light result. Also did the water off/on test suggested by Mo above and heard/felt no difference at all. Took a usb snake camera to the aftmost plug hole and examined raised exhaust valve and stem, and then tried the allen wrench trick. It has had a lot of MMO, even a bit of WD40, in it. No movement. Turned the engine a bit and tried again. I've run out of ideas.

[ndutton]

I've run out of ideas.

This isn't going to get better until the offending valve becomes unstuck. If you've exhausted (intended, sorry) the non-invasive methods that, depending on the severity of the stuck-ness, have not been successful you are left with partial engine disassembly, head, manifold, valve cover plate and valve removal, valve guide reaming and possible replacement as well as possible valve replacement.

At that point a decision needs to be made. As long as the engine is disassembled that far, as long as you've already ordered replacement head, valve cover, thermostat (if late model), manifold, exhaust flange and carburetor gaskets, as long as you have the valve spring compressor handy, do you address just the one stuck valve or go nuclear and do all eight? How often do you get in that deep? It's a question no one can answer but you.