Engine Vibration

[imported_TheMan]

Hey all,

First, I just wanted to say that I really enjoy this forum and all the great advice everyone has to share. Keep up the good work!

I have a 1989 SeaRay 180 open bow with the 3.0L mercruiser and alpha one outdrive. I have only been testing the boat with muffs as I have not had a chance to get to open water yet. At idle, the engine seems to have really excessive vibration. Unfortunately I do not know the extent of the travel, but it looks to be about an inch and a half side to side (rough guess). It also shakes the boat pretty well. I can only assume that this is more than is typically expected, but have only owned an OB before though, so perhaps I am wrong.

When the boat is placed in gear and RPMs increased to around 1000-1500, the rocking goes away and the everything seems to be running great. The boat doesn't shake much, the outdrive doesn't appear to move at all, and it is a lot more pleasant to see the engine sitting stationary. I have not increased the RPMs above that while on the muffs.

My question is: Are there potential problems other than improperly installed (or worn) engine mounts that would cause such a bad rocking? I assume that by engaging the gears the engine is essentially locked into place to transfer the power (probably also bad for the life of the drive shaft if it takes the vibration).
I am a little low on tools at the moment as I moved a short while ago and left many in my parents' garage. I have made sure that everything is as tight as can be when done by hand, but that is about as far as I can get till next weekend.

Any advice you guys can give is much appreciated!

 

[tommays]

Re: Engine Vibration

I can tell you even a new one shakes a Bit on a cold start if you dont warm it up around 1500 RPM but it should idle smooth in about 60 to 90 seconds


The first step would be a full tuneup and see how it runs then

I have no problem with it shakeing even at 600 RPM when its running correctly BUt it will never be as smooth as a V-6 or V-8


Tommays

 

[lrlima]

Re: Engine Vibration

I had a similiar problem with a 4.3 engine...after all of routine maintenance / tuneup items, turned out I lost compression on #6. If I was you, I'd do a compression check along with what tommys said just to be sure...

 

[Silvertip]

Re: Engine Vibration

Make sure it's firing on all four cylinders. It may have one cylinder out due to a bad valve or an ignition miss. Even with one cylinder out it will smooth out somewhat at anything above idle. Tune the thing up before going near the water. Start with a compression check as was suggested.

 

[QC]

Re: Engine Vibration

Just for fun I'd start with a cylinder balance test. Momentarily disconnect each of your engine's spark plug wires one at a time while the engine is running. When the plug wire is removed from the spark plug, there should be a big drop in idle speed and idle smoothness, especially with a 4 cylinder engine. When you pull a wire and there's little or no change in idle speed or quality, you've found the bad cylinder. If all act equally, then there is no single suspect cylinder at least at idle.

 

[imported_TheMan]

Re: Engine Vibration

Thanks guys! I will try QC's advice when I get home. Probably purchase a compression gauge later this week and get started on a tuneup. I'll let you know if anything turns up.

I've been thinking about buying a compression gauge to use on my car anyways. I know that Autozone has a $35 one, but I'm not sure on the quality. Anyone have some suggestions as to a decent gauge and the price? I can't imagine there would be a lot of variation between brands, just in bells and whistles.

 

[Bondo]

Re: Engine Vibration

Sears has Decent Gauges,.... At Decent Prices.......

 

[Zackman]

Re: Engine Vibration

Agree with what everyone else has posted. Just one other thought, if the other recommendations prove to be okay. Check the motor mounts, given the age and amount of shake you describe, one may have broken.

 

[imported_TheMan]

Re: Engine Vibration

Just a quick update this morning.

I followed the advice of QC and checked to make sure each cylinder was actually firing. The 3rd and 4th cylinders were not.

Had a few thoughts running through my head, which I tried to sort out. 1.) Blown rods? Nah, everything seems to be running okay, just irregularly. 2.) Bad plugs? Nah, guy I bought it from said he bought new ones and they looked new when I checked earlier. 3.) Bad distributor or wires? Maybe, but its not an overly complex system, so I doubt it. 4.) Dumbass hooked up plugs in wrong firing order? Quite possibly.

I checked the firing order, and sure enough, the guy seemed to have just randomly connected up the spark plug wires to the distributor. As noted, he said he changed the plugs because the boat wouldn't even run when he got it. My oversight as to not check the wiring prior though. Anywho, I reconnected them properly and the engine wasn't rocking at all. I'm hoping (and am 99% sure it will) that this also corrects the "low power" the guy reported when he tried using it.

Building off of that, anyone know if there is any expected damage as a result of running the boat with improper firing order other than poor performance? I am still planning on doing a compression check this weekend if it doesn't rain.

Thanks again.

 

[imported_TheMan]

Re: Engine Vibration

Didn't mean to have those faces in there, just tryin to note my thoughts.

Much happier now that the engine and boat aren't shaking to heck!

 

[QC]

Re: Engine Vibration

Cool, glad it worked out so far. Yes, that would also cause low power. Not sure about any damage although it for sure isn't good. I'm guessing the exhaust smelled pretty gassy though . . .

Those little faces happen whenever you follow a period with a close parentheses. Stupid. It gets me every time I put etc. at the end of a parenthetical thing . . .