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Old 03-08-2021, 08:46 PM
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Shake shake shake....

Hello Afourians, Recently my engine shakes shakes shakes! I regularly run the engine at the dock, if we don't go out, as is the case in January/February. This is at the dock in neutral, so prop and shaft are not moving. She shakes at all speeds although a bit smoother at higher revs, maybe. This is an engine with quite a bit of click-click, sometimes rumble, but now suddenly she vibrates the whole cockpit. What has happened? Your suggestions welcome.
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Old 03-08-2021, 10:09 PM
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Is it firing on all cylinders? You can try to remove the spark plug wires one at a time, while the engine is running (replace them before removing the next one). Each time you remove a wire, there should be a noticeable change in the sound of the engine, because that cylinder will not be firing. If there is no change when a wire is removed, that cylinder is probably not firing, and may cause vibration or shaking.

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Old 03-09-2021, 12:40 AM
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Did the vibration start after a maintenance\repair procedure? In particular any procedure that involved removal of the spark plug wires? If so check the firing order of the spark plug wires. It's easy to get #2 & 3 spark plug wires interchanged.
Also have a look inside the distributor cap for tracking (shorting) between the terminals.
Have a look at the spark plug wires at night while the engine is running to see if there is shorting between wires or shorting to the engine.
Feel the spark plugs. Are they all evenly warm after the engine has been running for awhile?
How long since the last tuneup? When was the advance last serviced? Kind of a long shot but since the engine seems to run a bit better at higher RPMs maybe the advance is stuck advanced position.

ex TRUE GRIT
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Old 03-09-2021, 10:43 AM
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Just to be clear...
This is while in NEUTRAL? The prop is NOT turning?
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Old 03-09-2021, 10:50 AM
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How long since a tune up?

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Old 03-10-2021, 07:15 AM
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motor mount?
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Old 03-16-2021, 09:31 PM
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I did check the order of the plugs, made darn sure prop is still, etc. Here ya go: There is no change in the sound when #4 and then aftmost #3 wires were lifted off. I did not expect that, since the engine sounds about normal, just shakes! Replaced distributor cap since I had a new one. Same result. I'll get a rotor, don't have a new one, to replace that too. EI so the tune-up is mostly that. Now I think I can eliminate the problem probably not motor mounts.
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Old 03-17-2021, 12:13 AM
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Compression check probably a good idea

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Old 03-17-2021, 06:46 AM
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Quote:
Originally Posted by DDO View Post
I did check the order of the plugs, made darn sure prop is still, etc. Here ya go: There is no change in the sound when #4 and then aftmost #3 wires were lifted off. I did not expect that, since the engine sounds about normal, just shakes! Replaced distributor cap since I had a new one. Same result. I'll get a rotor, don't have a new one, to replace that too. EI so the tune-up is mostly that. Now I think I can eliminate the problem probably not motor mounts.
Before getting into compression, I would try to swap wires + spark plugs around, to rule out wire or plug issues. But agree that this screams stuck valves, especially on 3 & 4, closer to exhaust. Is oil clean? no milky way?
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Old 03-17-2021, 09:34 AM
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DDO..for now, just clean up the contacts on the rotor..I wouldn't just start replacing a bunch of parts hoping for a miracle cure, which is just like stabbing in the dark.

I second surcouf's suggestion. Double check the wiring, 1-2-4-3 on the plugs as you go clockwise around the dizzy.

The first thing i WOULD replace, are the spark plugs..I try to remember to do mine every season when I do an oil change.
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Old 03-17-2021, 04:51 PM
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Thanks for all the guidance. Today I will just continue with the spring tune-up and put in the new plugs, some MMO in the holes, a new rotor carefully checked for fit. Valves sound very click-e-ty today. Sigh... Happy Saint Patrick's, all, from Mrs. O'Connor... Laphroaig will have to wait until I solve this!
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Old 03-17-2021, 08:49 PM
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The symptoms remain the same after the above work, so I think the next step is to try "stuck valve" treatments as scattered around this forum. Favorite treatments? What are the causes of "sticking"? Thanks.
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Old 03-18-2021, 04:47 AM
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Quote:
Originally Posted by DDO View Post
The symptoms remain the same after the above work, so I think the next step is to try "stuck valve" treatments as scattered around this forum. Favorite treatments? What are the causes of "sticking"? Thanks.
If plugs / wire tests failed, confirming no compression would be next step. Spray regularly and generously MMO / WD 40 etc.. trying to aim at valves. If you have access to the valve cover, you can try to lift a little more the stuck valves, it will help break the sticky gunk. Patience and spray...
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Old 03-18-2021, 05:39 PM
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Quote:
Originally Posted by Surcouf View Post
If plugs / wire tests failed, confirming no compression would be next step. ..
+1
Confirming compression\no compression is the next step. In addition to stuck valves there may be a blown gasket between 3 & 4. I don't know common this is or even if it ever happens - something to think about........

ex TRUE GRIT

Did you confirm after the repairs that the plugs are actually firing? A crude method is to take the wire off the plug and put a screw driver into the spark plug boot and see if you can jump a arc to the spark plug while the engine is running. Wear gloves so you don't get shocked to badly.
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Old 03-21-2021, 10:44 PM
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Today I did my first compression test: 105 95 97 0 (aftmost). Sigh. Slopped some MMO in aftmost hole and left it for another day. I am not sure what is next. So, each of #3 and #4 spark plug can be lifted off without changing the engine run, but 3 had compression of 97. Does that tell me something more? I am assuming now I have a stuck valve and should put spray Seafoam up the carb and MMO down the hole and what else? I am actually enjoying learning about more parts of the engine. I've spent time in most other sides...
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Old 03-22-2021, 12:30 AM
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# 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
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Old 03-22-2021, 05:08 PM
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Quote:
Originally Posted by JOHN COOKSON View Post
# 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.
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Old 03-22-2021, 10:32 PM
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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.
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Last edited by Mo; 03-22-2021 at 11:24 PM.
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Old 03-23-2021, 01:14 AM
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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?

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Old 03-23-2021, 02:43 AM
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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.)
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Old 03-23-2021, 06:48 PM
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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/for...ad.php?t=11680

Last edited by scratchee; 03-23-2021 at 06:50 PM.
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Old 03-23-2021, 07:16 PM
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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!
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Old 03-27-2021, 11:59 PM
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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?
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Old 03-28-2021, 11:08 AM
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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.
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Old 03-28-2021, 03:10 PM
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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...
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