hello all. I need ur professional opinion and would appreciate ur help.. I was going slow through the channel [like I should] and nothing of my fault a kayaker would not get out of the way, so I went around them on LOW TIDE and I ran aground . my motor started to bounce and motor hit sanding bottom .. When I went though and started to put her on plane ,it was good for a short time[ 5 minutes] Then I lost power.. my RPM were about 3000 but my MPH was about 10.. I fished for the day .but didn't go over 3000 RPM'S When I returned to the dock one of my neighbors said I may have blown my lower unit. Is that possible ? my propeller looked fine no chips motor sounded strong no kind of strange noises that I can hear.. If any can help me that would be great thank u
high rpm slow speed
- Thread starter against the wind
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Sounds like you spun the hub. There is a rubber center in the prop on most motors that is designed to prevent lower unit gear damage by slipping on the shaft. That can be rebuilt by a good prop shop at minimal cost. Put it in gear and try to turn the prop by hand on the trailer, engine off of course. If it has spun, you may, or may not, be able to make it slip, depending on how tight it remains.
Yup. Spun hub. If it ran normally for a bit and there is no prop damage that is what it is. Not a huge deal and not too expensive to fix.
Fishermanbb said:
Two seasons ago at slow idle speed I hit a submerged log that damaged the prop. My symptoms were a bit different, Top speed was fine but there was a vibration at low revs. That was due to a combination of a shifted hub and some blade distortion ( and not a lot. You couldn't see it but you could measure a difference from blade to blade)
Long and the short: Prop shop replaced hub and tuned prob. Cost was $225 a lot less than a new ss prop and the tuneup added 200 revs to the WOT speed.
thank u everyone. I was thinking spun hub also, but when i heard that i could have damaged my lower unit, well that made me very concerned. could u tell me the signs of a damaged lower unit ,also if i sucked alittle sand and mud up from being grounded could that be something to be concerned about.. thank u
The most common symptoms of lower unit probs are noise, vibrations or shifting issues. If there are vibrations that get stronger as revs increase that usually means that the prop shaft is bent ($$$). If the vibrations are more at low revs and diminish at higher revs, the prob is out of whack.against the wind said:
Sucking some sand is not a big deal, just keep an eye on the water flow (pee stream etc)
I know it's a bit scary experience but be glad you ran into sand and not rocks
Get your prop re-hubbed or replaced and enjoy.
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against the wind said:
If you had blown your lower unit, you would know it. It would be making all kinds of non-happy sounds, grinding, metal to metal noise or locked up totally. By you being able to still run the motor, in gear, at 3K rpm, your lower unit should be good. Anything over the 3K mark, you are putting pressure against the prop and hub to try and lift boat on plane, hence the motor revs but no increase in speed, spun hub.
As far as the sand/mud in the impeller. You're not the first to bump bottom with your motor. Did you flush it out after you got back? By you continuing on even at 3K, you probably flushed it out already. If it still concerns you, change it out one afternoon so you know it's ok, cheap/fairly easy to do.
Take a Sharpie and make a line across the black hub and the stainless steel or Al on the propeller. Give it some full power hole shots, and see if they still line up. If not, the hub is slipping.
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against the wind said:
Sorry, the impeller/water pump. If you are concerned about sucking up sand, gravel, mud when you bumped bottom.
Chances are you will be fine since you continued to run the boat, you have probably flushed out anything you might have sucked up in it. But if you still have question, you can change out the impeller, check out the housing and start again with a fresh impeller.
thank u ky grady.. Ijust changed pump this spring so I think impeller should be fine. I will mark hub and propeller tomorrow . I was more concerned about lower unit, however I feel alittle better by you and saesicks comments. like I said I really didn't hear any noise coming from lower unit but I am going to drop lower unit oil and see if I feel any metal shaving besides the very fine powder ones I did spin the prop today by hand and by eye it looked like it was turning straight when I hit the sand bar I wasn't going fast about 3 to 4 mph . so I'm feeling alittle better about lower unit damage
against the wind said:
You asked for help on this forum, and you got very good advice. Don't worry about your lower unit and don't waste any more time. No need to change the oil, it's fine.
Your problem is a spun prop hub as stated above. THE HUB DID WHAT IT IS DESIGNED TO DO and broke free, saving your lower unit from damage.
Just pull your prop and take it to a prop shop to get re-hubbed.....in one day and for about 100 bucks you will be back in business....
I am 100% sure of this, it happened while I was fishing on my buddy's boat recently, one of the prop hubs spun and we had to come back 15 miles on one motor.
thank u finest kind.i appreciate that . I was debating to drop the oil or not just to make sure. but I see ur point. as I mentioned the prop shaft looks straight no noise in motor that I could here. sending out prop on Monday to get re hubbed. when you rehub a prop is it just as good as a factory installed hub or could u spin it again with normal use. just curious
That is an interesting question. Make sure that you ask if there is a waiting time for the rehubbed prop before installing it. Some hubs are pressed but mine required a urethane filler that was poured in. It needed two days to cure. Is a rehub as strong as the factory hub? Maybe yes, maybe no. The bottom line as mentioned is that if you hit something hard and especially if you run a stainless prop, you want the hub to 'break' and not transfer all that force to the LU shaft and gears.against the wind said:
Now over time, hubs can also age and the bushings dry out. You never really know until something happens or doesn't
I may not have mentioned that sometimes a hub moves a bit but doesn't continue to spin under load. That is what mine did a year or so ago. So the usual symptom of the motor seeming to over rev but without an increase n speed was not present. It just felt like something was wrong since the hub bushing after 'twisting' was not perfectly centered and the prop had a slight imbalance that was noticeable only at low speeds. I could feel it in my feet.
i agree seasick. I took my hub to a shop yesterday, it wasnt poured it was pressed in and done in 15 minutes. Is pouring better ? The one thing that was intresting was they asked me was i shore i spun the prop because he told me most all yamaha props when spun come out very easy. he said mine was very hard to come out and was doubting i spun the hub. i thought that was intresting he said that.
against the wind said:
So, don't keep us in suspense...is your problem solved now with the re-hubbed prop or not?
got rehubbed acouple of days ago, have not put her in the water yet hopefully this week.. dropped LU oil no shavings and no play in shaft ill keep u updated.