Hard to describe my problem, but I will try. When I accelarate or turn, the engine rpm stays up but it seems like something is slipping in my lower unit. What are the possible problems?
That would sound like you have a cavitation issue.
At least the first guess.
possible causes could be
the motor doesn't stick down far enough behind the boat
(check to see if that horizontal plate like section above propeller is about even with bottom of boat)
The motor might be adjusted out too far at the bottom from trying to get the front of the boat up to go fast.
The propeller has flat blades and needs some cup.
Or there may be some other issue such as irregular boat bottom, or something in the flow to, and through the propeller to cause turbulance.
I was also gonna say sun hub, but should the rpm climb then? When I corner with my engine trimmed high for a straight line I can hear the prop start to gurgle, and eventually partially climb out of the water. This is accompanied by a sudden climb in rpm.
I've never had a spun hub, so I don't know what that would sound like.
It's very easy to diagnose through. Using a white marker, or nail polish. Paint a straight line from your prop hub, over the retaining washer, over the retaining nut, to the center of the drive shaft. Take the boat for a spin and make it do what you described. When you get back to shore, inspect you line. If the line is now broken you have a spun hub.
it is a 1987 tracker with this mariner 45. I purchased this boat in April 06. I did replace the prop this summer after the other prop was damaged. My point is the boat and motor was a pair forever. Am I correct that an engine is direct drive from the the gears to the prop?
it is a 1987 tracker with this mariner 45. I purchased this boat in April 06. I did replace the prop this summer after the other prop was damaged. My point is the boat and motor was a pair forever. Am I correct that an engine is direct drive from the the gears to the prop?
Almost. It's direct drive from the crank shaft to the prop shaft. But between the prop shaft and the actual prop is a replacable hub. It"s meant to "spin" itself ie slip. For when the prop hits something underwater the hub will slip thus reducing the shock put through to the engine and minimizing damage to the prop itself.
took the boat out today and tried it. Like was suggested, I marked the shaft nut, lock washer and prop. Once I was going into a very strong wind and whitcap waves, the slippage almost stopped me on the water. The painted marks were still in line with each other.
I put on a new prop this summer. The new hub just slipped on the splined shaft, with nut and washer to prevent the nut from coming loose.
I am not familiar with a prop hub. Is this still a possibility?
Does your engine rpm go up, down, or stay the same when the event occurs? Any unfamiliar noises?
Did the problem start when you put on the new prop? How long before or after the prop installation did the problem start? Was the hub replaced when the prop was replaced? Is the new prop the exact same dimensions as the old prop? Diameter and pitch. What do you do to get out of the event? Do you just keep going full throttle and it goes away by itself?
I will try to answer your questions 1 at a time.
1. Engine rpm goes up slightly or stays the same, definitely does not go down.
2. No unfamiliar noise.
3. We spent a week vacation on the lake this summer. It started during that week. When I loaded the boat to come home I noticed the old prop was damaged.
4. I think I matched the new prop to the old prop by matching the numbers, diameter and pitch.
5.When the problem happens I reduce the throttle and then gradually accelerate.
6. Did not replace the hub. Again I am not familiar with the hub. I slid the new prop over the spline shaft and secured it with nut and washer that prevents the nut from coming loose. The new prop exhausts through the prop.
Is the prop hub inside the lower unit?
I apologize for not being to sharp on this subject
Last edited by artee : October 22nd, 2007 at 08:24 PM.
Reason: spelling
Hi Artee,
The prop hub is actually a rubber bushing that sits between the prop and the splined shaft. Or let me add more detail.
If I were to install my prop from scratch:
1) Slide big copper washer with tapered hole onto the splined prop shaft.
2) Fit rubber prop hub into aluminium prop
3) Slide prop (complete with rubber hub) onto prop shaft
4) Fit brass interface bushing onto splined propshaft and engage with rubber prop hub.
5) Fit tongued washer
6) Fit Nyloc prop nut and tighten
7) Bend 3 tongues to engage with brass interface bushing.
It's that rubber hub that we're refering to. I hope you have this setup.
here's a nice pic of the lot. The biggest component (rear of pic) is the rubber prop hub
Double checked my old and new prop. They appear to be a perfect match. The new prop is a Michigan Match #031016, it is a 10 5/8 inch diameter x 12 pitch. It does not have the rubber prop hub, a brass or bronze sleeve with splines is pressed into the aluminum prop. The splines on the shaft and prop are good.
The old prop is not original, don't know what the original prop was.
I am not the sharpest knife in the drawer, by any means, but I am a toolmaker by trade. So I do have some mechanical background. But I don't see anything with the prop that is causing this problem.
Maybe I will get a nice weekend and get out and try some things.
Thank you very much for trying to help me with this problem
No problem Artee. Sorry I couldn't help you figure it out though. My knowledge of LU's are limited, but I don't think there anything like a cluth in there that can slip. Not without making a noise anyways.
obviously something is slipping. Without noise that would make a toolmaker jump overboard it could only be
1. Hub assembly slipping.
2. Prop slip in the water.
The symptoms you describe seem to allude to the second choice. You say that by the numbers the props are the same. You also said that the problem appeared when the original prop was damaged.
here's my theory. The motor is mounted high to increase performance by running the prop near the surface. This also increases prop slip, especially when turning, or accelerating. If the prop is cupped, this slippage is reduced. If that cupped prop is then damaged, it likely will slip. A replacement prop with less or no cup would slip.
Look closely at the trailing edges of both props. I would bet the original has been custom cupped.
Another possibility is that the bottom of the boat was damaged at the same time the prop got bent, and the problem is the boat, not the prop. If the same obstruction that got the prop put a cup in the bottom of the boat near the transom, it would act like you describe.
MARINER 45 -spinning my wheels
Linear Mode
