Strange Clunking - What could it be from??

[mejim707]

This is a 96 Seadoo Challenger with a single Rotax 787.

I've been battling with a strange "clunk" at idle for years. I've been trying to find the source but I can't. When I open the back I can't hear it over the engine so it's near impossible to locate the source, but when I close the hood I hear it clear as day. I don't think it's coming from the engine because this was happening the exact same way with the old engine. No difference.

Things I've checked / done;

• All mounts are new.
• All cables / wires including the large steering cable are totally secure. I've also added foam around the steering cable when it makes contact with the body.
• All exhaust parts are completely secure.
• Installed an "anti-rattle" cone on the pump.
• Drive shaft has 2 brand new rubber bumpers.
• All hatches are secure. In fact I've added weather stripping around them to be positive.

Here is a video of the clunking sounds. It sounds like a golf ball bouncing around in a wooden box. It's only really there when the engine is idling causing the boat to shake. And it sounds like it's coming form the rear but everything is secure I think.

Any ideas would be great! Maybe one of you have had the same and figured it out?

Here is the video -> Clunking Sound While Idling

 

[mikidymac]

It is a seadoo and they all do it at idle. It is just the design of the jet pump and the "Anti-Rattle" cone kits really don't fix it either.
Just the way it is so try and ignore it.

 

[mejim707]

It is a seadoo and they all do it at idle. It is just the design of the jet pump and the "Anti-Rattle" cone kits really don't fix it either.
Just the way it is so try and ignore it.

I’ll try lol But man it’s annoying and when I have passengers they all say ‘that doesn’t sound good ’

I try to tell them it’s normal but they think the engine is failing lol It sounds soo good at 1800 RPM though. Kinda just humms. 1500 and it sounds like a failing engine. It was the same with the last engine too so you’re probably right it’s just the cone.

Thanks!

 

[etemplet]

key is to identify the "frequency" of the vibration. Is it exactly at engine RPM and does it increase with RPM. Sounds like it fades out. If that sound was there with the old engine I wouldn't worry about the engine internals causing the problem

Now what you could have is a bottomed out bolt on an engine mount. Sometimes the bolt is just a tad too long and it is difficut to spot. It seems that it is tight but it is bottomed. I'd get in the hull with the engine idling and pull on it hard left and right to see if the knock changes. You said the knock was the same with the old engine in place. I'll bet that what the problem is. Check those mounts (the long bolts and the short ones). Sometimes when you change the shim height to line up the engine.... the bolts can be too long or too short. Good Luck !!

I got two of these engines to align.... Oh Boy.

 

[mejim707]

key is to identify the "frequency" of the vibration. Is it exactly at engine RPM and does it increase with RPM. Sounds like it fades out. If that sound was there with the old engine I wouldn't worry about the engine internals causing the problem

Now what you could have is a bottomed out bolt on an engine mount. Sometimes the bolt is just a tad too long and it is difficut to spot. It seems that it is tight but it is bottomed. I'd get in the hull with the engine idling and pull on it hard left and right to see if the knock changes. You said the knock was the same with the old engine in place. I'll bet that what the problem is. Check those mounts (the long bolts and the short ones). Sometimes when you change the shim height to line up the engine.... the bolts can be too long or too short. Good Luck !!

I got two of these engines to align.... Oh Boy.

That's a very interesting thought! I'll check if any of the bolts are anything but properly seated against the mounts. When I'm installing anything, I pay very close attention to any possible anomaly. I think I would have noticed something strange like that but I'll recheck!

 

[mejim707]

It is a seadoo and they all do it at idle. It is just the design of the jet pump and the "Anti-Rattle" cone kits really don't fix it either.
Just the way it is so try and ignore it.

I ordered this anti-rattle kit from OSD Marine

Anti-Rattle Kit

Question though, on the engine alignment all I see is about aligning it to the alignment tool. But I have not seen anything about the distance from the pump / impeller to the PTO. I didn't think to check that since nothing I've seen about alignments suggested that. Or maybe I just absolutely missed it.

I saw you mention something about that in a different thread, to make sure the rubber bumpers aren't so tight to get crushed. I have not, nor have ever, checked for this...

What is your advice?

 

[mikidymac]

There is no spec distance from the pump to the engine, they can't move enough to cause an issue.
The rubber bumpers do get crushed and is why they get replaced.