rattling and cavitation

[jdsgrog]

Ok, Here's the deal. The first issue I have is a rattling noise. When I am running at my upper rpms, I get a rattling noise. I'm not sure how serious it is as it doesn't seem to cause any issues with performance (actually, after tuning the motor up this year, I am getting 3-4 mph faster than last). I've had the boat out three times running the motor a total of about 6 hours. The funny thing, though, is that when there is tension on the steering rod/cable, the rattling goes away until the rod/cable is loose. Any thoughts?

The second issue happened briefly today. Reading from other posts, it seems like cavitation, but I'm not quite sure (never experienced it before). I was running at WOT when suddenly my speed suddenly dropped and the engine revved up. When I pulled back on the throttle, it ran fine, but when I took it up to WOT again, it happened again. So I decided to stop to check if the prop was ok. It seemed fine. Ran the motor again, puttered around for a little and stopped to fish for a little. Didn't have the problem again all day even at wot.

Any thoughts would help. Thanks

Motor: '67 Johnson 33hp

 

[F_R]

Re: rattling and cavitation

Props hubs don't self-heal, only get worse. Must have been cavitation. 33s cavitate easy. All it takes is a piece of grass looped around the lower unit on some boats/installations.

Anybody would have to be on-site to diagnose where the rattle is coming from. Seems like it might be looseness in the steering?

 

[jdsgrog]

Re: rattling and cavitation

I was thinking it was cavitation. Actually the two times it happened, I was in an area where there was a lot of submergent weeds. Once I left that area, the boat seemed to run fine. But I wanted to make sure to calm any uneasiness.

I guess, I'll check the steering when I go out next time. I know it's not in the powerhead, so I figure it must be something loose. Just not quite sure what it is.

Thanks.

 

[Matrex]

Re: rattling and cavitation

I had a similar cavitation-like problem that progressively worsened... I would lose "bite" with the engine revving, but no power being transfered to the water. It initially showed up occasionally when starting from a standing start under load such as when pulling a tube. It eventually got to the point where it would do the same as you described when just motoring down the river.

My first boat, so I was worried it was something serious. Brought it into the marina and the mechanic took about 2 minutes to pop off my prop and show me the rubber inner hub that goes on the "drive shaft" had separated from the steel prop assembly. They put a new prop on and problem was solved. They sent my broken prop out to have a new hub assembly installed. I just got it back last weekend, re-installed it and it worked great.

Hopefully you have figured it out on your boat, but if not something you might look at....

 

[jdsgrog]

Re: rattling and cavitation

prop hub assembly? From what I recall, my propeller doesn't seem to have what is described. It has a pin that goes through the drive shaft and the propeller hub. A very simple set up.

 

[F_R]

Re: rattling and cavitation

jdsgrog, your prop does have a rubber cushion between the hub and propeller itself. You can't see it but it is in there, and they do come loose sometimes...commonly referred to as a "spun prop". However, as I said earlier, once they break free they don't heal..only get worse, eventually to the point where it won't go at all.

You clinched my cavitation diagnosis with the statement that it was weedy water. I believe the word for it is %#@#**&!!, pure and simple. Happens constantly here in the swamps. Stop, put it in reverse to clear the weeds, back to forward and move on to the next weed.

 

[matt9923]

Re: rattling and cavitation

I have nasty weeds right in front of my house. i have my own launch on the reservoir. It works for skis haven't tried my boat but should work. I usually use my atv but sometimes the jeep. Last yea rit was so bad i took my canoe out and had a steel rake and cleared a nice area was about 5 canoe fulls. Its just your steering cable or near the pulley i had to cut out some fiberglass cause the pulley rubbed. Whats this cavitation thing? The propeller falls off the shaft? How much to fix?

 

[jdsgrog]

Re: rattling and cavitation

I've been out a few times since my last post. I still hear the rattling, but still can't figure it out exactly. It's not the steering cable. Actually, I'm wondering if it's the water splashing when planing. But I'm not too concerned. Maybe need to retrim? Anyway, I've been out some nine or ten hours and haven't had anything break on me.

As for cavitation. Haven't had the problem at all since. matt...were you asking what cavitation is? I could try to explain, but it's better just to google it or look on this forum. The propeller hub problem is a different issue, but I found that it was not the problem.

 

[Dunaruna]

Re: rattling and cavitation

Gentlemen, what you are describing is either a spun prop or ventilation, not cavitation.