I've developed a knock. Advice needed

[OldNBold51]

here are the details: This is my 1st I/O but many years of wrenching under my belt on cars/outboards/dirt bikes.

95 wellcraft 232. 7.4L engine with 55 hrs on rebuild. I'm the second owner with total of 55 hrs me owning. I've no history or maintenance schedule to reference but during rebuild all the bellows and gimble looked and felt good.

The shutter flaps have been an issue since I got it and I know and hear them distinctly at low rpms pretty often. I don't think (I could be wrong) this is the problem.

While cruising along at 2800 rpms, the 1st thing i heard was a whining/hydraulic/belt whining sound that I slowed and listened to. I was close to the dock so i kept going. Within 5 minutes of the whining it turned into a knock that sounded like it's coming from engine.

I trailered boat and yesterday changed the oil to see if it was a lifter.

OIL psi: 40+ at idle and this hasn't changed since day 1
Idleing in gear or out of gear no noise, no knock sounds great.
Neutral: can rev to any rpm w/o the knock (an occasional shutter valve knock)
In gear : can idle speed (no wake) w/o knocking but can hear an intermittent / occasional whining like previously described.
Holeshot: here comes the knock, steady and consistent.

What do you think guys? Is this in my gimble bearing as the noise sounds like it's coming from the engine bay.

 

[sethjon]

Re: I've developed a knock. Advice needed

here are the details: This is my 1st I/O but many years of wrenching under my belt on cars/outboards/dirt bikes.

95 wellcraft 232. 7.4L engine with 55 hrs on rebuild. I'm the second owner with total of 55 hrs me owning. I've no history or maintenance schedule to reference but during rebuild all the bellows and gimble looked and felt good.

The shutter flaps have been an issue since I got it and I know and hear them distinctly at low rpms pretty often. I don't think (I could be wrong) this is the problem.

While cruising along at 2800 rpms, the 1st thing i heard was a whining/hydraulic/belt whining sound that I slowed and listened to. I was close to the dock so i kept going. Within 5 minutes of the whining it turned into a knock that sounded like it's coming from engine.

I trailered boat and yesterday changed the oil to see if it was a lifter.

OIL psi: 40+ at idle and this hasn't changed since day 1
Idleing in gear or out of gear no noise, no knock sounds great.
Neutral: can rev to any rpm w/o the knock (an occasional shutter valve knock)
In gear : can idle speed (no wake) w/o knocking but can hear an intermittent / occasional whining like previously described.
Holeshot: here comes the knock, steady and consistent.

What do you think guys? Is this in my gimble bearing as the noise sounds like it's coming from the engine bay.

The only way to tell for sure is pull the OD. Its an easy job for a wrench like yourself and the problem should be easy to find. Make sure you have a manual as opposed to trying it without.

 

[JustJason]

Re: I've developed a knock. Advice needed

Finding a noise is only something you can find, and not diagnoseable over the internet. Your best bet may be to have someone you trust drive the boat someplace not congested and you'll have to have a mechanics stethoscope on the block to pinpoint the noise. If you have rod or bottom end knock the engine probably wasn't measured out correctly during the "rebuild".

 

[OldNBold51]

Re: I've developed a knock. Advice needed

Finding a noise is only something you can find, and not diagnoseable over the internet. Your best bet may be to have someone you trust drive the boat someplace not congested and you'll have to have a mechanics stethoscope on the block to pinpoint the noise. If you have rod or bottom end knock the engine probably wasn't measured out correctly during the "rebuild".

Based on the symptoms, doesn't it sound like it's something other than the engine? the reason i say that is there is no knock from the engine at any rpm's unless there is a significant load on it. Won't a rod or a crank knock all the time, just more pronounced under a heavy load? If it's a spun bearing or a loose rod cap bolt won't the oil pressure drop significantly? I may well be wrong here, but i'm trying to maximize my efforts and rule out some things. I know a loose or cracked flywheel will knock, but i thought it knocked continuously too.

I'm not arguing here, i'm just trying to rule some things out.

 

[OldNBold51]

Re: I've developed a knock. Advice needed

So I took the OD off hoping to find something glaring at me. U Joints seemed fine with no grittiness or slack.

the gimbal bearing I'm unsure of. while it had plenty of grease and it spun freely w/o any rough/grit feel. it did seem to have some up/down/side play. with the alignment bar all the way in and contacting spline in coupler, I could see a few .000's of movement in the inner race up/down. That's strictly "eyeballing" it. It moved, but not a lot. the alignment bar also fit slightly loosely in the bore of the bearing. Also, when you pulled backward the alignment bar out of the splines, you could get much more movement from the bearing.

I don't want to destroy this bearing if it doesn't need replacing.

How much tolerance is acceptable for the gimbal bearing?

 

[Bondo]

Re: I've developed a knock. Advice needed

So I took the OD off hoping to find something glaring at me. U Joints seemed fine with no grittiness or slack.

Ayuh,.... Did you drain the outdrive, 'n inspect it's oil,..??

 

[OldNBold51]

Re: I've developed a knock. Advice needed

Ayuh,.... Did you drain the outdrive, 'n inspect it's oil,..??

I drained about a cup w/o any signs of metal. None.

Update: so i removed all the spark plugs. 6 looked like they had 55 hrs on them, while 1 looked like 0 hrs and the second only a small amount of carbon anywhere. Suspect cylinders are 2 and 8. I also had a mist when engine spun over coming from 2 (although it smelled like gas). Compression check yielded all cylinders were within 6 psi of each other at avg 145 psi. Suspecting i had water getting past my intake manifold gaskets, I checked torque on the manifold bolts. While all bolts were loose, well under the 45 ft/lbs torque , #2 had less than 20 ft/lbs torque and #8 not much better. I tightened them all down to spec, put dirty plugs into 2 and 8 and started her up. I now had a small knock/ more a lifter tap than knock while in neutral which wasn't there before. I took her to the water for a load test and she didn't pass as still a knock, although sounds different than before. I gave up for the day at that point.

Has it been others experience that once the intake manifold gasket leaks, it needs replaced, not just tightened? I had my stethiscope out but couldn't pinpoint the source. It was loudest while on the valve covers, but the covers are a giant amplifier so I didn't put much into that.

Also, this motor was briefly hot when impeller went out and 1st inkling of problems was when the horn went off. I immediately shut down. After the impeller was fixed, I put 2 hrs of run time on this before the knocking started.

I know these pic's are kinda blurry, but 2 and 8 are much cleaner than 4 and 6. #2's ground strap was spotless, even shiny. 8 was clean, but not as clean as 2.

 

[Bondo]

Re: I've developed a knock. Advice needed

#2's ground strap was spotless, even shiny. 8 was clean, but not as clean as 2.

Ayuh,.... Extremely Clean sparklpugs is a sign of Water in the combustion chamber....

 

[OldNBold51]

Re: I've developed a knock. Advice needed

After changing the intake manifold gaskets without any relief from the knocking under load, I borrowed a leak down test gauge.

The good news was I did a great job of sealing the rings as I had less than 5% leakdown on 7 cylinders. ( I used the dry break in method)

The bad news is I had a huge leakdown in #5 that varied from 25% to 55% depending on which way I turned the crank to get to TDC. So I suspect I've a broken piston.

It looks like I've got me another project to keep me busy.

So far owning this boat: 55 hrs of run time and over 100 hrs of working on it!!!