Super Jet SN SuperJet - Vibration at Low RPM

[Fleabags]

Guys,
Last season, I experienced some vibration at low RPM (1995 SJ). Probably not a big deal. Others that rode it, didn't even notice. I am pretty particular about my stuff and have no issue spending a little money each year so I never have any days/weekends that are cut short due to something that I saw coming.


My first instinct is to replace the "original" rubber coupler damper and realign/shim the motor. Any reason to believe the motor mounts would be going bad on a very low hour stock machine? BTW, the impeller is a new SS re-pitch & balance from impros, so I feel pretty confident the vibration is not from that.

Also, Any issue with the aftermarket rubber dampers? They are 1/3 the price of stock.

Any insight is appreciated - THANKS

 

[Dirtybird]

Had a similar problem my self.
I found it to be the pipe just making contact with the hull.
Or maybe any part of your motor rubbing along something.

 

[Fleabags]

Thanks Dirtybird,
My problem definitely feels more like a balance issue. As the RPMs go up, it seems to balance out and is not noticeable. Unfortunately, I am storing my ski about 2 hours away and can't just go out and fire it up. I wanted to order some parts, so when I get it home I get after it.

 

[IS0LD0UT]

Is is running rough? Is the idle set low?

 

[Fleabags]

Runs/idles well. When I stated "Vibration at Low RPM" I should have clarified. IMO, all skis tend to vibrate at idle, especially out of the water.

This vibration is somewhere above idle RPM and while under load. For instance, it is most noticable when going through a "no wake" zone when you are giving it a little throttle.

THANKS

 

[Fleabags]

I'd like to resurrect this post. I didn't ride all that much this year, however, the problem still exists. Only noticeable when riding slow in no wake. The ski runs great and idles smooth so I am confident it is not due to a rough running motor. It feels like a balance / out of alignment issue.
I removed the coupler shroud and checked shaft alignment. It appears to be right on. No visible signs of coupler wear or rubber dusts from wear.
Like I mentioned, once I go above say 10mph, you can't feel it at all. That being said, when you have to go a long way in a no wake zone, it is very annoying and can't be good for it.
Would like to work on it in the off - season - Any ideas?
THANKS

 

[tor*p*do]

pull the pump, check the pump bearings and seal to hull
also may as well pull the motor (forward) and check the midshaft
I bet you find rough bearings or a blown pump seal

 

[Fleabags]

thanks
It a 95, so it wouldn't hurt to do that anyway. Should I buy all OEM parts or do you know of a source for the bearings, etc?

 

[Fleabags]

I just looked at the schematic - this could get expensive if I try to replace everything. Do you think I'll find noticeable wear to the bearings in order to determine what needs to be replaced? Assuming that this is the issue.

 

[tor*p*do]

if it is the pump or midshaft, you will feel the bearings being rough of the midshaft housing will be visually seperated
Jetmaniac for the win on rebuilding either

 

[SkiDiggity]

My sn does it too only in the 5 mph zone, I have replaced all of my pump bearings and have a new midshaft, midshaft housing and drive shaft and it still does it, however my other 94 does not. I think it is a shimming issue, but i am having a hard time getting the motor to align correctly.

I just found this video made by wamaltins and I am going to go home and try this tonight. I will update you if it solves the issue.

Make sure you watch part 2 as well.

 

[Fleabags]

Thanks for the info.
I pulled my motor and removed the mid shaft. I then shimmd the pump to align the drive shaft directly in the middle of the hole in the firewall. Re-installed the midshaft and then re-aligned the motor. Vibration went away.

 

[SkiDiggity]

So when you realigned the motor did your couplers match up perfectly all the way around? i can't seem to get mine to line up just perfect and i am worried about destroying the mid shaft housing again.

 

[Fleabags]

I didn't have any issue shimming/aligning the motor. However, my problem was the pump alignment. The drive shaft, where it enters the engine comparment, was sitting low. I shimmed the back of the pump to bring the shaft up. I'm sure that was the issue, since I had shimmed my motor before thinking that may have been where my vibration was coming from. However, it was right on.

 

[Fleabags]

THE VIBRATION IS BACK.
I mostly ride lakes where there is little to no "No Wake" zones, so I hardly ever ride the ski in the RPM range where the vibration occurs. This past weekend, I was in a mile long no wake zone heading out to Lake Michigan. The vibration was really bad. It occurs just above idle speed and everything shakes until you speed up or slow down.
The ski runs awesome and the vibration has nothing to do with the motor not running well. It starts easy and idles smooth. It pulls hard and you would never notice the vibration when powering from idle to plane, since it goes so quickly through the RPM range where the issue exists. No vibration when out of the water, only under load.

Two seasons ago, I pulled the motor and realigned the driveshaft. It was only a little off, but I did notice an improvement and thought the problem was fixed. The main shaft bearings seemed smooth and I didn't notice any play. I purchased a new (aftermarket) coupler damper but the OEM one looked perfect with no wear marks, rubber dust or imperfections. So, I left it in rather than risk putting an inferior aftermarket one on.

I'm ready to pull and align the pump and motor again, but don't fell optimistic that it will do any good. Do motor mounts wear out without failing? Not knowing any better, it feels like the motor mounts are weak. I inspected them when I pulled the motor and they looked fine.

Any insight is appreciated.

 

[Midlake Crisis]

I had a similar problem that included a loose motor mount

 

[Andersschroder]

Im interested in hearing about if you solved it? I have the same problem


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[Fleabags]

With Michigan Summer's so short, I decided to deal with it until the weather turns cold or until something breaks. I'll update the thread once I tear it apart.

 

[Mdavies_02]

I pulled my engine on my SuperFreak w/ Front foothold (Super tight engine compartment on PTO Side) in 16 minutes last weekend. I think you should address this issue before it breaks regardless of the length of your season. Better to lose a day now in my opinion. Either way good luck

 

[Andersschroder]

Im interested in hearing about if you solved it? I have the same problem


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I figured out my vibration was due to a completely mangled motor mount.


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