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

[RCD_Wake]

Hi all, This is my first time on this forum -- and I am *hoping* to be a Supra owner very soon (depending on answers to the below ha)...

Hoping for a little bit of help here. I test drove a 2005 21v today with the Indmar "assault" 325 5.7L, 230 hrs per the dash, no maintenance records to speak of. There was a knocking at idle and low RPMs, not sure that it completely went away at higher RPMs / under load, but it was definitely harder to hear (with the compartment closed it was completely undetectable -even hard to hear at idle - with it open it was still tough to hear if the knocking was even happening anything above ~2500 rpm). Based on some research it sounded almost like it could be a rod knocking, but I am a bit too novice to really be able to identify 100%, plus it didn't get louder or worse with high RPMs and the engine under load (including after filling the 1250lb ballast). I've asked the dealer for info/diagnostics on it, but since they're trying to sell me the boat I'm not certain I trust their diagnosis.

The dealer did say they inspected and compression tested the engine and everything checked out, though I have not personally seen the results. The knocking was relatively mild but definitely not something they would miss. On the test drive, the boat ran and performed beautifully other than the knock, even had a very smooth and normal idle (maybe 600-700rpm). It is also in phenomenal condition (garage kept practically show room condition boat), so I'm trying to determine if the knocking is a reason not to buy.

Couple of questions:
- Would the compression test detect something wrong with a rod?
- Could the compression testing detect any kind of OTHER (non rod) knocking problem?
- Are there other common piston-knocking sounds that are not as major as a rod issue?
- Would a rod knocking issue ever be an easy or cheap fix (from the research it sounds pretty major across the board)?
- Any idea on a ballpark repair cost if it IS a rod (considering its not something I am skilled enough to do myself)?

- What other questions should I be asking about this to probe the dealer and help figure out my level of risk?

Thanks for the help!

[RCD_Wake]

One thing I thought I should add --

This is being sold by a Malibu dealership (certified Indmar service center) who says they "certify" all of their preowned boats, which includes the inspection/compression test. I have asked for a formal diagnosis of the knocking by one of their Indmar mechanics before I agree to buy. Not sure if knowing that it is an official Indmar service center changes anyone's thoughts on this.

I am speaking to the mechanic on Monday or Tuesday of next week, would love to hear some feedback before then.

[tg0824SSVGG]

I had a "knocking" that was a bad head gasket -- it was easy to fix (it was under warranty at the time) - but would not have been had I ignored it.

[RCD_Wake]

Thanks for the reply.

Any idea if a bad head gasket would show up in a compression test?

Were there any other symptoms other than the knocking (ie, white smoke, the smell normally associated with a blown head gasket, etc.)?

Nice boat by the way

[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.