Rhythmic Optimax 135 Vibrations

[Chipper1012]

Thanks in advance for taking the time to read and weigh-in.

Serial #: OT834066
2004 Optimax 135 XL SWB
798 hours

I've noticed for almost a year now, that my motor presents a vibration that is rhythmic in nature. Every 5 seconds the motor will shake, then smooth out, then shake...over and over. This is felt both out of gear and in gear. The faster I go (or higher in rpm) the shorter the interval between vibrations gets.

Again, it's done this for about a year, and I've finally decided to dig into the issue. I replaced the plugs, no change. Clipped a timing light to the plug wires to see if I could find a coil mis-firing at the intervals, no luck. Cleaned the crank position sensor teeth, thinking it was a timing issue, nothing.

Fuel pressure while at idle is 87, Air is 77. Thought this might be a touch low. Hooked regulated air to the shrader valve. Air dumps through the exhaust at 77 psi, anything lower than that it holds and I cannot hear any leaks through the spark plug holes.

Tracker looks good after carefully inspecting.

So, I decided to check the heartbeat and do a compression test. Here are the results from the first go-around (running temp/throttle wide open/all plugs out/by the book):

1: 83
2: 85
3: 90
4: 105
5: 90
6: 70

Yep, good ol' #6. Not wanting to believe it, I soaked the cylinders in seafoam and Marvel Mystery oil overnight. It made clouds of white smoke the next day. I warmed it up and tested again to see if I could loosen up a stuck ring:

1: 90
2: 90
3: 100
4: 105
5: 95
6: 80

While #6 came up a little, it's still the black sheep.

What's the general opinion? Time for a rebuild? Are the vibrations symptoms of having a weak cylinder? Boat runs great otherwise, but definitely would want to stop short of completely blowing her if this is a good warning...

Here's a video for a better example.

[leonreno]

First, are the compression numbers stated in order taken? If so, I would recommend doing them again and checking #6 first, helps rule out a weak battery. If it still is as low this time then I would either pull heads and check the gaskets or use a bore scope and look at them through the spark plug holes. Might be a good time to inspect the plugs, see if the #6 plug looks and different than the others.

[Chipper1012]

No, they are not in order. I took the port side first 2,4,6 then starboard 1,3,5. Battery shouldn't be an issue. It's only a few months old and I had it plugged to the onboard charger while testing.

I pulled the plugs this evening after making a few runs on the lake. All the plugs had a nice golden-brown color to them. #6 didn't look any different than the others.

I'll definitely take a look with a scope or pull the head to get a visual before tearing this thing apart. I hate that it ran so good this afternoon, but that vibration paired with newly found low compression has me worried.

Maybe it'll just be a head gasket repair...knock on wood. Regardless, I'm thinking of sending my injectors (air and fuel) to Don. In my mind I'm thinking I might have a few out of calibration that cause the vibration, who knows.

[lpugh]

Time to rebuild or replace, even if you #6 up, you still have issues. Will cost a lot less to address the now than waiting for additional damage

[EuropeanAM]

Before you tear the engine apart, I would suggest you make an attempt at using POWER TUNE in the engine.

This is a Mercury Product.

Note: Recommend you keep in mind that any plug run with Power Tune will almost certainly be replaced soon after. DON'T run a brand new set of plugs for this purpose for the obvious (financial) reasons.

-Warm engine up to temp

-Remove spark plugs

-Tilt engine to FULL UP position and support it.

-Spray power tune into the spark plug openings (liberally).

-Reinstall spark plugs and leave engine sit OVERNIGHT.

-Next day, Launch, Warmup and run for at least 10 minutes on water.

REPEAT PROCESS (AT LEAST ONCE), then Retest compression. If #6 is still below specs, the cylinder head should be removed to inspect to determine correct actions to address (cylinder head o-ring, sticking Direct Injector, rebuild, etc).

[Chipper1012]

Thanks, Don. I appreciate your feedback and will definitely give it one last shot with the power tune.

Like I said, if this does result in a tear down due to a damaged piston, cylinder, etc. I'll be sure to send you my fuel rail and injectors for a cleaning to start off on the right foot after the rebuild.

[lpugh]

Perform a leak down test before a tear down to identfy the source

[Heff]

Chipper, did the power tune work?

[Chipper1012]

Heff, sorry for the delay in responding. I’ve been stalling trying to figure out a good time to rebuild, but I think I got lucky.

So, the Powertune/Marvel Mystery Oil/SeaFoam helped a little. When I first tested compression, CYL #6 was at 70psi and I got it to come up to 80. Still lower than it needs to be. A few days ago I took off the heads to visually inspect. I was expecting to
see scoring on CYL #6 but to my surprise it looked very good. Still had some hone marks on the walls. Also, I was amazed at how clean all my water passages were considering my motor was used in salt the first 10 years. Anyways, more on that later.

Currently, the heads are off and I’m waiting for new O-rings for the heads and the water jacket seal. I did notice while disassembling that I had oil dripping from the head just below CYL #6. I believe my problem was a compromised o-ring on that cylinder. I have since flattened the heads using glass and sandpaper. I’ll post the compression results once everything is reinstalled.

Question? Does anyone know how to recoat the heads with that yellow coating present in the water jacket. It looks like a corrosion inhibitor. Can I coat the CYL head mating surfaces with Alodine? The original coating was removed when I resurfaced the heads with glass and sandpaper.

Chipper

[EuropeanAM]

Yellow coating is a product Mercury uses in their corrosion inhibiting process, and they are quite tight-lipped about it's contents or makeup.

Hopefully you did not remove any material from the head surface- as the o-ring channels must be cut precisely the same amount as the head.

Head bolts are a one-time use bolt (torque to yield fastener).