Alpha Vibrations

[Danny C]

2004 Chap 220ssi with Merc 350 MAG MPI and Alpha 1. I replaced the impeller over the winter and now I can feel an unusual vibration in reverse and idle. Then Saturday while running back in a storm I was getting slight vibration and noise running at 3500 rpm. I trimmed up and the vibration completely stopped and it was smooth as glass but I also immediately lost 5mph (on the dash speedo). That has me a bit confused. Thinking maybe I was spinning the hub a bit? When I pulled the boat and checked, the prop seems tight and don't see any play in shaft. Plan on swapping the prop and trying again this weekend. Any thoughts/suggestions? could it be something I did when I pulled the LU and swapped the impeller? maybe didn't put it back together perfectly? Gonna go check the LU oil now.

 

[H20Rat]

Hubs usually don't slip just a bit... They are slip, slip, GONE. Does it make noise when you turn, especially a sharp turn? When you said the prop is tight, did you check the nut for proper torque or did you mean tight on the shaft if you try turning it?

 

[Danny C]

The more I am looking into it, the more I believe it may be a worn hub. The symptoms are exactly what some other people are describing. I am dreading the cost/time to replace...

 

[Scott06]

The more I am looking into it, the more I believe it may be a worn hub. The symptoms are exactly what some other people are describing. I am dreading the cost/time to replace...

Do you mean a prop hub or coupler? Prop hub is no big deal to replace , but I think the modern hubs are work or not no slip.

If just in reverse or idle Id suspect a tune up issue such that engine isn't as smooth. At speed, usually a vibration that changes with trim is gimbal or u joint related. Speed dropping when trim up is more likely related to less water flow into the speedo pick up tube, notoriously inaccurate.

Just dropping the lower wouldn't cause a vibration. Would suspect looking at removing drive to inspect gimbal bearing and ujoints, but if it's not bad I'd probably just keep an eye on it until fall.

 

[Danny C]

You are correct, i meant worn drive coupler. Symptoms such as vibrations, unusual speed fluctuations at diff trim levels and one i did not mention was burning plastic rubber smell when that happened. Originally wrote it off as a nearby camp fire because tgere were several but now think it is related after reading other peoples accounts.

 

[Scott06]

Burning rubber is likely the coupler. Look for rubber bits by the coupler on back of engine

May not be as bad as you think to change , you don't have to remove the engine only slide it forward and or rotate to get at the flywheel cover. Would check the drive alignment before and after as it is likely culprit.

 

[Danny C]

Thanks for the info guys. Also, I failed to mention that this day in particular I spent most of the day, 2 hrs or so, just idling around to look at lake lots for sale. I am also hearing that idling is not great for the coupler, maybe this pushed it over the edge. Then on my fast cruise back to the dock it started to let loose.