knock on '05 21v w/ Indmar 325 - boat shopping

[RCD_Wake]

Just got the compression readings:

1 - 165
2 - 150
3 - 150
4 - 155
5 - 160
6 - 155
7 - 150
8 - 155

within about 10% but all seemingly on the low side (I believe it should be in range of 150-190, so this is at the bottom)

[michael hunter]

A compression test has nothing to do with a knock. A compression test checks the seal of the piston to the cyl , head gasket and valves. There are many things in an engine that can cause a knock unforgettably most are expensive and will require the engine to be removed and disassembled. Is this boat at a dealer? Will they give you a written warranty concerning the knock? Will they allow an independent surveyor to check it for you? A knock can be a nothing to worry about or a major problem if you have to replace the engine you will spend as much as 10,000 dollars. Make sure you know what is causing it before you buy. Where is the boat?

[CJD]

Knocking is a very generic description. If you could locate it to a general area it would help. Some things that can cause a knocking:

1) Rod bearing loose or worn.
2) Main bearing worn or spinning.
3) Piston slap from loose clearance.
4) Lifter gone flat from low oil pressure or gunk in the system.
5) Loose coupling for the prop...loose prop...although it won't be loose for long!
6) Flex plate springs broken or missing.
7) Tranny or V-drive issue.

Those are just some things quickly off the top of my head. A compression check will not diagnose any of them. All of them require at least some disassembly to diagnose. If I hear noises like a real knocking, I would walk away. Since it is a dealer, and if it is a really good deal otherwise...get them to warranty the engine bottom end and drive train for a year. If you use the boat hard next summer, any real knocking will grow to a full scale break down by then!

Remember, prices will continue to drop on boats at least through February, as families try to cover Christmas expenses. There is no reason to hurry into a deal unless you are confident about it.

[RCD_Wake]

Thanks for the feedback guys, it definitely helps. I already assumed what you both said re: the compression test...wanted to hear it from somewhere other than my gut / research.

CJD, as far as where the noise is, I definitely don't think it has to do with the v-drive / tranny or prop coupling, as it was happening out of gear as well. It was definitely coming from the engine and was definitely synced in timing with the RPMs, so I imagine it was something happening internally. Hard to say if it was coming from the top end or bottom end in there.

I think your suggestions on a warranty for just the engine or bottom end are awesome suggestions, and I hadn't thought of them previously so thanks for the help. I think the boat is a great deal otherwise -- I am getting ~$37K from NADA as far as value, and I am seeing similar boats out there listed in the $30-$38K range, I'm hoping to walk away with it for WELL under $30K (we have agreed contingent upon what their mechanic diagnosis). It is in practically show room condition, other than the wiring between the amp and tower speakers needing some work, and the depth sounder read out screen seems to be shot.

I will try to get the boat running again and see if I can't more closely identify where (specifically) the engine noise is.

[DAFF]

Make an offer with the cost of a rebuild or new engine deducted from the price. Hope for the best but plan for the worst case scenario. Sometimes taking an educated risk works out in the long run.

[RCD_Wake]

Mechanic at the dealer just came back and said there is "nothing out of normal operation" that they are detecting and are "not able to reproduce the sound." Now they are starting to sound like a car dealership!

Daff -- I am either going to do that or ask them to warranty it for 100hrs. I am also going to run the boat again this week, will see if I can identify exactly where it is coming from.

[michael hunter]

Were you there when their mechanic looked at it and found nothing?
Can you bring an independent engine mechanic to check it out?
Where is the boat?

[wotan2525]

"Knocking" our misfiring can also be caused by bad gas. Always a possibility for a boat that has been sitting for a while.

[RCD_Wake]

I was not there -- I am going to run the boat with the mechanic so we can listen/talk through it together - hopefully tomorrow morning.

They did say the boat wasn't used much in the couple of seasons prior to the previous owner trading it in (and it is an 05 with only 230hrs on it.. so it is believable) -- so you're right maybe it was the gas, I'll ask if they put any additives in or anything that 'made the sound go away.'

Thanks for the input and thoughts on this, I know there are a million possibilities for diagnosis here, the input I've gotten has helped guide me to push for the right things and ask the right questions. I'll report back on when I meet with the mechanic to run the boat together.

[CornRickey]

Warranties are only worth the paper they are written on especially if it is a dealer specific warranty. Unless your willing to sue them and pay the costs to do so they have the upper hand. Don't even mention bankruptcy court. Do you value the next summer @ the savings you are getting on the boat? Because worst case scenario is it will be in the shop. And that's even if they honor the warranty. There is a ton of boats out there. Find one that doesn't have a problem. Or at least has a problem you personally can fix. I got educated on third party warranties when I talked to a service rep at a stealership. It was open your eyes.