Knock Knock and I don't know whose there.

Whfd74

Cadet
Joined
Nov 3, 2008
Messages
7
I have an 01 horizon f/s. Recently it has developed a lound knock in the rear of the engine. I took it to a shop that told me the engine had a lower end knock. I removed then engine (3.0 VP with an sx 2.16 drive) and rebuilt the lower end. Everything was replaced back to factory spec. Then engine was bench ran and made no noises. Placed the engine back in the boat and when taken back out to the water still had the knock. I did not break down any of the lower unit parts. We did notice a leak in the exhaust bellows (about a 1/2" hole in between the ribs). I have no idea of where to start to look for this or what to start to do to diagnose the problem. When we removed the engine we did notice alot of grease on the engine coupler. It looked like it had been slung from inside the splines. Also how hard is it to drop the lower unit and rebuild it all. Any help I can get on this would be a big thanks including places to buy parts and common parts to replace on these. THANK YOU!
 

P 0 P E Y E

Chief Petty Officer
Joined
Jun 3, 2009
Messages
441
Re: Knock Knock and I don't know whose there.

Is it the same knocking sound?

Sounds like the mechanic who sold you the engine may have heard and identified the noise as opportunity knocking and sold you an engine when you only needed a center bearing.

Please excuse my sarcasm. I just hate to hear another case of bad troubleshooting by a "professional" or a case of all that work and it's still broke.

Did you perfom the work yourself?

Hope you can track it down quick and enjoy the summer.
 

TilliamWe

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Dec 21, 2004
Messages
6,579
Re: Knock Knock and I don't know whose there.

Just out of curiosity, what did the exhaust shutter in the exhaust pipe look like? You know the one inside the boat, inside the metal pipe, that is made of metal surrounded by rubber, that will clunk, clank, clink, rattle when the rubber melts off after an overheat? Not all VPs have them, but if yours does, it could be the very simple culprit.
Nothing like an engine rebuild for a $20, mostly unecessary part!
 

gadget73

Petty Officer 1st Class
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Jun 20, 2009
Messages
308
Re: Knock Knock and I don't know whose there.

If its not the exhaust shutter, I'd suspect the U joints, especially if the bellows is leaking.


Just a side note, what I've done in the past to help diagnose engine noise is to use a timing light to guage whether its every revolution, or every other revolution. If the timing light blinks once per noise, its valvetrain. If the noise happens twice for every blink, its bottom end. If it follows no special pattern, its likely not internal. Mind you this is by no means definitive, but it sometimes does help narrow things down.
 

TilliamWe

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Dec 21, 2004
Messages
6,579
Re: Knock Knock and I don't know whose there.

Just a side note, what I've done in the past to help diagnose engine noise is to use a timing light to guage whether its every revolution, or every other revolution. If the timing light blinks once per noise, its valvetrain. If the noise happens twice for every blink, its bottom end. If it follows no special pattern, its likely not internal...

You sir are a practical Genius! Would you like to run for public office?!
 

Whfd74

Cadet
Joined
Nov 3, 2008
Messages
7
Re: Knock Knock and I don't know whose there.

Yes I did the engine rebuild myself. I hate paying some jackleg mechanic charging $90.00 an hour when I can do the work myself and know its not done just to make a quick buck. The exhaust has a threaded "star shaped" metal piece that rest inside the riser. The engine is the original for the boat. Like I said there was no noise when the engine was ran outside of the boat on the stand. Idled fine, came up to operating temp and would rev up and come straight back to idle with no noises or hiccups. I saw the reply about the u joint and I know I have had them go out in trucks before and always had more of a whine, but then again never had to be at the angles an outdrive is. The bellowes I have leaking are the exhaust so will that still effect the drive side of it. Thank Guys for all of the help.
 

rjlipscomb

Chief Petty Officer
Joined
Jun 2, 2009
Messages
582
Re: Knock Knock and I don't know whose there.

My experience is that bad u-joints tend to knock. Bad bearings tend to whine.
 

gadget73

Petty Officer 1st Class
Joined
Jun 20, 2009
Messages
308
Re: Knock Knock and I don't know whose there.

Oh, exhaust bellows. No, that won't affect the drive. I thought you meant the drive bellows was leaking, allowing water to come into contact with the U joint. That really jacks them up. I'd still pull them and give them a good looking at though. I've also had them tend to knock and clack when they fail.

Something else you could do, fire the motor with the drive off. That will tell you if its something associated with thedrive, or if its in the exhaust. Just need a water source for the engine, probably you can just pull the hose off the transom assembly and stick a garden hose in there.
 

TilliamWe

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Joined
Dec 21, 2004
Messages
6,579
Re: Knock Knock and I don't know whose there.

"The exhaust has a threaded "star shaped" metal piece that rest inside the riser."

And would it bang against the side the the exhaust pipe?

Again gadget has the right idea, remove the drive and start the engine, this would eliminate the drive as the source. Not too hard to jam a garden hose into the hose end in the transom plate. Might want to have someone hold it just in case.
 

Whfd74

Cadet
Joined
Nov 3, 2008
Messages
7
Re: Knock Knock and I don't know whose there.

Engine has been stand run with no noise. I am going to drop the lower unit replace u-joint, seals and bellows while I have it down. I am just wondering how hard is it to pull the lower unit do I have to remove it from the engine bay side or does it unbolt from the outside. This is my first I/O boat and I haven't got a shop manual yet and won't be here by the time I get the chance to work on my boat. I have limited time to work on this because of my work schedule for the next two months (48hrs on duty 24hrs off). Any help would be great.
 
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