2002 Ski Nautique - GT40 Vibration / Power Loss

[fsts2k]

I have had the Ski Nautique 2002 w/ a GT40 since 2020 and overall it has been a good boat. This summer the boat has run well until the last day when I was putting it away for the season.

Pulling the boat off the lift, I put the boat in gear I had a noticeable vibration albeit a bit different than a bent prop, it just didn't feel as smooth as normal. Once the boat was up to temp I took it to full power and the vibration seemed to get a bit better.. Then about 6 min into full power down the lake (~45 mph) the boat engine pitch changed and slowed down a bit... it would only go about 41 mph. I pulled back the power to idle, then went full throttle again and was able to get back to 45.

After getting the boat on the trailer I inspected the prop, it looked perfect. I realize that a prop can be bent without any visual queues but the vibration was different than what my 226 feels like with a bent prop. It almost makes me suspect a fuel flow issue or perhaps plugs.

We didn't get to use the boat as much this year as years past which is what is making me think a plug is fouled or lack of fuel.

Thoughts?

[gary s]

Well not knowing where you are or what has been done to the boat in the past this spring I would do a cap and rotor change along with the plugs. Could be something simple like condensation in the distributor or a plug going bad. Did you go through the boat since you have had it? fuel filter, impeller, trans oil change etc?

[fsts2k]

Thanks, the boat is in South Central Wisconsin, I am in Chicago. I have gone through the boat over the past few years including redoing the gelcoat, new gauges, etc. The mechanic I use in Wisconsin also went through the mechanics last Spring. We have done impeller (twice), multiple oil and fluid changes, etc; aka normal maintenance each year. I am unsure on the fuel filter but will ask about that and cap and rotor; makes sense.

I probably should have started with my thread on the boat.. it is here:
https://www.planetnautique.com/vb5/f...ique-196/page5

Note that I did replace the ECU two years ago when it was burned out.

[fsts2k]

Figured it out this weekend. The clamp holding the distributor cap to the adapter came loose allowing the cap to come up, I think it was missing a cylinder. New cap, rotor, plugs, and wires now; seems to be back to normal

[fsts2k]

Ok, something is still wrong as I am getting vibration when driving. The motor runs super smooth when in neutral after the new cap, rotor, plugs, and wires. I am now thinking the issue is the prop. Last summer the boat was positioned too far on the lift and the prop was over the horizontal crossmember; when the lift came up it lifted the boat from the prop. I am thinking that is when it happened, hoping it is the prop and not the shaft.

The boat (2002 Ski Nautique with GT40 engine) was purchased with a three blade prop. I don’t know why it has that prop or if it was replaced. Everything I have seen is to use an ACME 422 prop which is a four blade for this boat. Assume that is still the direction to go?

Besides pulling the boat and positioning an indicator on the shaft to check runout is there any other way to see if we bent the shaft vs the prop? Current symptoms are that the wheel has a vibration at ~30mph and you can “hear” a bit of vibration. It is also possible to feel the vibration through the hull (e.g. arm resting on the hull) while under power.

Thank you
Kevin

[Rednucleus]

Need to check prop, shaft and strut for damage. I would not run it again until fixed.

[fsts2k]

Just checked again.. clearly see one of the three prop blades is turned in a bit; aka bent. Would make sense why it vibrates like it does. Ordering a new 422 now.

[Tom_H]

A bent ear will certainly cause vibration. If you're ordering a new one, send the old one off for repair and keep it around as a spare. You should still check the shaft/strut. A pretty simple way is to tape some solid gauge wire to the bottom of the boat, and point the loose end right at the center of the shaft end. Rotate the shaft end and see if the shaft end moves relative to the wire. If it does, your shaft is bent. The strut is generally easy to eyeball, but since you should do an engine alignment anyway, split the coupler behind the transmission. If the shaft displaces a bunch when you separate those, you likely have a bent strut (or a really bad engine alignment (also verify that your shaft is centered in the through-hull shaft log)).

[fsts2k]

Thanks, new 422 going on tomorrow with mechanic.. he is going to check shaft and strut. Will know after that if vibration is gone

Appreciate the help!