Loud Transmission Knocking Noise

S

Stylish Imports

New Member
Mar 1, 2022
5
Perth Western Australia
Boat Info
Boatless
Engines
Boatless
G'day all, I am looking at purchasing a 2001 Sea Ray 340 Sundance. Today while we were doing a pre purchase mechanical inspection we noticed a loud knocking sound coming from the port side gearbox. It only does it on the port and not stbd and it's pretty loud as you can hear in the video.
What do you guys think is the issue? The same port engine has also a compression issue. When the mechanics performed the compression test the lowest reading on 2 cylinders was around 105 psi and the highest on the other 6 cylinders was around 185/190 psi.
Would you guys run away or get the costs deducted?

https://youtube.com/shorts/vWAAQNGElRI?feature=share
 
V-drives are known for a few "normal", but sometimes unsettling, sounds but I don't think your video is showing one of those sounds. That sounds awful. I assume it's not making that noise when not in gear?

It's a tough market out there so walking away from boats is not easy. Unless you plan on using this boat as a floating cottage (only) I'd make sure that the current owner addresses that as part of the deal (preferred) or you get enough money off asking price to fully address it.

Compression...others will surely chime in. I seem to recall 10% difference between cylinders is acceptable? You seem to be well beyond that level.
 
Stee6043 said:
V-drives are known for a few "normal", but sometimes unsettling, sounds but I don't think your video is showing one of those sounds. That sounds awful. I assume it's not making that noise when not in gear?

It's a tough market out there so walking away from boats is not easy. Unless you plan on using this boat as a floating cottage (only) I'd make sure that the current owner addresses that as part of the deal (preferred) or you get enough money off asking price to fully address it.

Compression...others will surely chime in. I seem to recall 10% difference between cylinders is acceptable? You seem to be well beyond that level.
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Yes the noise goes away when not in gear. And yes I have read all the other posts about similar issue but the noise this one made was super load and definitely not normal since only one side did it as well.

yeah the compression issue is huge, it probably needs a new engine rebuild or new heads.
 
Port.
1 - 185psi.
2 - 185psi.
3 - 115psi.
4 - 190psi.
5 - 185psi.
6 - 125psi Went down to 105 when warm
7 - 175psi.
8 - 185psi.
Compressions did not change when engines at temp.
 
V-Drives have a damper plate installed between the engine and transmission to help absorb impulse/vibration from the engine at low RPM, and will occasionally produce a knocking sound if they are wearing out, or failing. However, that’s the worst I’ve ever heard…by a far margin. Bad compression on a couple cylinders could make it worse.

I think you have 2 problems possibly. I’m guessing based solely on listening.

This compression numbers could mean a bad head, bad risers or both, and possibly piston ring issues. You don’t mention which engine, but your likely looking at heads and risers on both sides. And if you having issues with one side…the other is usually not far behind.

Damper plate needs replacement. This requires splitting the transmission from the engine, and possibly pulling the whole assembly.

I think you need a lot more information before purchasing.
 
I listened to the video, unless the seller is going to fix it, or at a minimum get it diagnosed, I would walk. That is not the usual knocking noise I am used to, plus you have low/inconsistent compression in cylinders 3 and 6. Could be resolved with a head/valve job, but that's a risk I personally would not assume.
 
The engine issue would bother me more, at this point. It actually could be causing that noise in the transmission or damper plate, especially if cylinders 3 and 6 are adjacent in the firing order (1-8-4-3-6-5-7-2??). Those compression numbers are definitely cause for concern.
 
km1125 said:
The engine issue would bother me more, at this point. It actually could be causing that noise in the transmission or damper plate, especially if cylinders 3 and 6 are adjacent in the firing order (1-8-4-3-6-5-7-2??). Those compression numbers are definitely cause for concern.
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Agreed, I walked away from a boat last year that had low compression in one cylinder. I asked the seller to do a scope and/or leak down test, to validate a bad valve and not a cylinder issue; they would not, so I walked. Broker kept saying a valve/head job was all that was needed. Some on here beat me up for walking/asking, but I felt good about my decision.

To your question "Would you guys run away or get the costs deducted?". I'd ask the seller to validate/diagnosis what's wrong. I am surprised they let you go as far as you did knowing this as in my opinion this did not show itself for the first time when you got on the boat. The seller is going to have to do this anyway for all prospective buyers. Once you know what's wrong you can ask them to fix it, you can deduct the cost from the price, walk, or negotiate a compromise (split the costs maybe) if you otherwise like the boat.
 
I have heard many transmission noises that are normal. That is one of the loudest noises I have heard from a tranny. Definitely warrants more investigation. Also, something is up with engine. Should be fixed before you buy.
 
Stylish Imports said:
6 - 125psi Went down to 105 when warm
Click to expand...
This would make me walk away. the fact compression goes down like that makes me think rings/piston issues rather than just valve train. Its sort of clear the knocking is engine not transmission. Doesnt say above how you know its transmission isolated. Wondering if thats just a guess from owner.
 
I do not think that is the standard damper plate rattle, sounds way too deep to me. If it goes away by bumping RPM at idle, then it could still be the damper. Engine scares me a little, If the boat has been sitting for a while, that can throw off the numbers. A hard run at 3k RPM for awhile might help.
 
Stylish Imports said:
Port.
1 - 185psi.
2 - 185psi.
3 - 115psi.
4 - 190psi.
5 - 185psi.
6 - 125psi Went down to 105 when warm
7 - 175psi.
8 - 185psi.
Compressions did not change when engines at temp.
Click to expand...

Without listening to the video, the 4 and 6 cylinders are middle of the engine right next to one another. I can promise you the inner wall of the exhaust riser is leaking water in to those cylinders and has caused the valves to tulip and possibly those cylinder walls are shot as well.

Can't speak to the klunking, possibly engine, bad main from the water intrusion, but I think the above is enough to walk away, actually run away from that one.
 
89P270 said:
This would make me walk away. the fact compression goes down like that makes me think rings/piston issues rather than just valve train. Its sort of clear the knocking is engine not transmission. Doesnt say above how you know its transmission isolated. Wondering if thats just a guess from owner.
Click to expand...
Tight valve?
 
Being a broker, with the availability of boats right now, if the rest of the boat is in great shape. I would recommend getting prices to repair, add 20% for miscalculations and frustration of waiting for repairs to be done. Then you have a boat you at least know these items are right. Keep in mind, we are talking 20 year old boat. Just my .02
 
bahamabreisus said:
Being a broker, with the availability of boats right now, if the rest of the boat is in great shape. I would recommend getting prices to repair, add 20% for miscalculations and frustration of waiting for repairs to be done. Then you have a boat you at least know these items are right. Keep in mind, we are talking 20 year old boat. Just my .02
Click to expand...
Contract has been cancelled, the owner deemed the knocking noise normal and he wasn’t willing to rectify or deduct the cost of the compression issue. I honestly don’t understand how he expects anyone to buy it, especially when he is asking over AU$120k +.
 
Stylish Imports said:
Contract has been cancelled, the owner deemed the knocking noise normal and he wasn’t willing to rectify or deduct the cost of the compression issue. I honestly don’t understand how he expects anyone to buy it, especially when he is asking over AU$120k +.
Click to expand...
I don't know how the market is in your neck of the woods, but here in the US I have had two boats sold out from under me because I wanted a survey and sea trial. Other buyers did not. Go figure.
 
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