Knocking sound in hull, low idle and a loose exhaust bolt. (Pic and Video included)

[Krispy]

So this past weekend I took my new to me ski out for sea trials, all was successful except I had my engine idle set too low.

In the water it was idling about 1000 rpm. At this RPM the engine would shake a bit, much like having a large "Cam" in a car. At these idle speeds there was a knocking against the hull that I couldn't identify. This knocking went away at about 1500 rpm.

This is something that I can't reproduce on the hose as the engine speed is much greater than 1500 without load on the pump.

I checked all the engine mounting bolts, all are tight. I did however find the bolt that wasn't fully seated (circled in red).



It appears to be cross threaded slightly into the engine and I can't seem to access it with any of my tools with enough torque to back it off. Any suggestions?

Could this be the cause of the problem?

When I tug on the engine and exhaust nothing seems to contact the hull. But something sure is makcing a racket at these low idle speeds.

Check the Youtube Video.

[video=youtube;n9Svh1z5rFs]http://www.youtube.com/watch?v=n9Svh1z5rFs[/video]

The Youtube video is still uploading but should be online shortly...

 

[Spimothy Leary]

that's the exhaust bushing... you can't back it out ?
it should be a metric hex nut... you should be able to reach it with one of the long hex sockets, or a long allen wrench...
and your sure the drive shaft isn't bumping the hull ?

 

[Krispy]

It is slightly cross threaded in the hole. I currently use a metric hex socket (short)



But I can't seem to get a good placement of a tool in there.

I wonder if I need to remove the *other* part of the exhaust pipe to better access it.

My plan is.

1. Get it out.

2. Chase the threads with a tap (M8x???)

3. Put it back together.

Unfortunately I am stuck at step one.

To be honest I didn't think about the drive shaft. How would I check that?

Does it make sense that it would go away after idle speed?

 

[get_real]

Did you look all through the hull front & back to see if something like a paddle or part was loose and was hitting the hull when the engine was vibrating at the low idle?

 

[Spimothy Leary]

the socket I had in mind was this one...

or even the ball end ones..

cheap at HF...

and don't be dumb and do what I did once and bought SAE, because you think they fit but they'll strip out that bolt in 1/4 turn... totally pissed me off...

i assume while its ideling you've done the obvious.. put your hand between the pipe and hull, or pulled a little on the pipe to see if its rattling against the bracket ? To be honest I've seen more than one ski that was running w/o that bushing in at all...not advisable, but not surprising either.. and you may want/need a new exhaust bushing there.. (really cheap, I get them at jet-world.net)

i had a drive shaft rattle at low rpm's way back when I bought mine, but it was fairly obvious where the sound was coming from...

 

[Seadoobuddy]

This could be a long shot but I once had a knocking sound in my hull also.
It turned out to be part # 37 in the diagram above. The bigger nut part was hitting the hull, I loosen it and moved it a little and the knocking went away.

Sorry but I can't help you with the cross threaded bolt.
Hey spim, did chuck lose a long wobble head allen wrench while working on mine? I found one during the 3rd cleaning of the hull last week.

 

[kicker]

. The impeller and driveshafts will have a rattle to it as well, which is normal. In 97 they put an antirattle cone in which helps a little. Make sure the driveshaft is greased, which helps with the rattle but does not eliminate it in most cases.

That being said it does sound more like a clunking then a rattle. Check your motor mounts, especially the right rear, that one seems to loosen first

 

[Krispy]

the socket I had in mind was this one...

or even the ball end ones..

cheap at HF...

and don't be dumb and do what I did once and bought SAE, because you think they fit but they'll strip out that bolt in 1/4 turn... totally pissed me off...

i assume while its ideling you've done the obvious.. put your hand between the pipe and hull, or pulled a little on the pipe to see if its rattling against the bracket ? To be honest I've seen more than one ski that was running w/o that bushing in at all...not advisable, but not surprising either.. and you may want/need a new exhaust bushing there.. (really cheap, I get them at jet-world.net)

i had a drive shaft rattle at low rpm's way back when I bought mine, but it was fairly obvious where the sound was coming from...

This sound appears to be coming from the front of the ski. In the video I had pulled out the storage bin as it sounded to me that it could be my tool kit banging around in there. It wasn't.

I found that my local home depot had those tools in stock, and for a few bucks more than HF I figured I would go on my lunch break to pick them up.

They seem like the right tool for the job.



When I got there I found someone in tools, showed them the printout. And they proceded to tell me that "it is a new product" and "I don't know where they are" a lunch break of searching later and still no tool.

 

[Krispy]

This could be a long shot but I once had a knocking sound in my hull also.
It turned out to be part # 37 in the diagram above. The bigger nut part was hitting the hull, I loosen it and moved it a little and the knocking went away.


.

Not a long shot at all. I will check that #37 as soon as I am home from work. It is possible that the clamp was tightened in a strange place. What is the correct orientation for that anyway? It seems like I need to be a double jointed pygmy of a man to reach some of these fasteners.

 

[Krispy]

...snip...

and don't be dumb and do what I did once and bought SAE, because you think they fit but they'll strip out that bolt in 1/4 turn... totally pissed me off...
...snip..

I just realized I am sitting in the middle of a factory that builds cars using all metric fasteners. Surely someone around here has the tool I need.

Anyone know what size the hex is that fits this? I am guessing a 5 or 6 mm as the thread major dia is M8...

 

[kicker]

6mm, try it get one 6 inches total length, then the ratchet will clear the top of the head.

 

[racerxxx]

I use the short Allen sockets like first pictured, an extension, and a 3/8" ratchet with an adjustable angle short handle from craftsman. Fits like a glove and use a cheater pipe if I need to. Take your plus out so you don't bloody your knuckles, been there, done that, and watch the temp sensor too. Check the large band clamp that its in the correct location, you might need to rotate the clamp to get the clamp portion away from the body, again I use the adjustable short handle ratchet. My 96 has a nice dig in the glass right there.



Sent from my SGH-T989 using Tapatalk 2

 

[Krispy]

Thanks for all the tips, I was able to remove it using the long Allen socket. Nothing like having the right tool for the job.

I Check the exhaust clamp, number 37 in the diagram. It appears as though it has plenty of clearance all the way around.

I will chase the threads, replace the bolt and try again.

Do y'all think I can try and turn the idle speed way down to try to re-create this knock on the trailer?

 

[kicker]

Try grounding your spark plugs and just turning it over with the starter and see if anything is bouncing around.
Pay close attention to the motor mounts and exhaust mounts.

Are your gas and oil tank straps secure? Or handle bar and steering mounts.

I'm running out of ideas.

Sent using Tapatalk

 

[Krispy]

Now the bolt is replaced, there is one tight spot on the secondary part of the pipe against the hull.

If it is the pipe hitting this is where it would be in my opinion

I am going to try using some closed cell foam to see if that changes anything

I'll report back.

 

[Krispy]

Nothing that seems excessive right?

[video=youtube;8RK5gF-AJrI]http://www.youtube.com/watch?v=8RK5gF-AJrI[/video]

 

[Krispy]

double post

 

[CReynoldsMIZ]

Grab ahold of the exhaust manifold and try and shake the whole engine. It shouldnt really move

 

[Krispy]

When I pull on the pipe and brace against the port side of the hull there is some slight movement, I am pulling hard enough that it is flexing the port side of the hull. That may be the movement.

 

[ski-d00]

sounds like the standard seadoo pump knock. very normal in all older skis. you won't recreate it on the trailer and it will go away with a slightly higher rpm. it's nothing to worry about, just ride it.

you can try the anti rattle kits which help sometimes but they will all do it 1000 rpms, your idle should be set at 1500 rpms.

 

[Krispy]

sounds like the standard seadoo pump knock. very normal in all older skis. you won't recreate it on the trailer and it will go away with a slightly higher rpm. it's nothing to worry about, just ride it.

you can try the anti rattle kits which help sometimes but they will all do it 1000 rpms, your idle should be set at 1500 rpms.

Thanks for the feedback, I was aware of the anti rattle kits but I thought that was a lighter knock from the pump area. Can anyone else confirm one way or the other?

Setting the idle speed seems to be a little bit tricky on this ski. I understand it should be 3k out of water and 1500 in water.

When on the trailer how are yall setting the idle?

1. Do you just start it and just let it go to idle and adjust to 3k?

2. Or do you start it, blip the throttle a few times and then adjust to 3k?

I seem to end up with lower idle speeds when I use method 2 over method 1.

 

[DA080682]

Thanks for the feedback, I was aware of the anti rattle kits but I thought that was a lighter knock from the pump area. Can anyone else confirm one way or the other?

Setting the idle speed seems to be a little bit tricky on this ski. I understand it should be 3k out of water and 1500 in water.

When on the trailer how are yall setting the idle?

1. Do you just start it and just let it go to idle and adjust to 3k?

2. Or do you start it, blip the throttle a few times and then adjust to 3k?

I seem to end up with lower idle speeds when I use method 2 over method 1.

I set my idle in the water after riding it for a bit so the engine is nice and warm. I don't really care what it does out of the water. Having the idle too low in the water will definitely induce a drive shaft knock regardless if you have the bumpers and pusher cone.

 

[Krispy]

I set my idle in the water after riding it for a bit so the engine is nice and warm. I don't really care what it does out of the water. Having the idle too low in the water will definitely induce a drive shaft knock regardless if you have the bumpers and pusher cone.

Getting to the idle adjuster on my 96 is a bit tough with the airbox on. I like your method though.

 

[DA080682]

Getting to the idle adjuster on my 96 is a bit tough with the airbox on. I like your method though.

On my GSX i just reach around the bracket from the front of the engine and get my finger on the t-handle enough to get it adjusted. The 97xp is a challenge to not sink the thing in the process because once you lift the hood and lean forward enough the nose goes under water.

 

[kicker]

Here is a tip. The next time you can get at your idle screw, cut a small piece of 1/4" fuel line and slice the one end about 3/4" long. Slide that end over the T valve (idle screw) and put a tie wrap around the end. The fuel line will stick past the carb bracket so you can reach it easier. Here is a picture looking at the setup from the bottom of the carb.