I have an 8 horse Hatatsu long shaft outboard on my C27. This just started this weekend. With low rpm I back out, move into the lane going out into the bay; just as I leave the channel and bring up the rpm to go haul speed it is as if the “clutch” starts to slip. The engine rpm winds out and I loose thrust. When I lower the rpm, it is as if the prop bites in again and gives me thrust. Outboards don’t have “clutch” do they? If the shear pin broke I shouldn’t have any thrust. Where should I start?
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Robert Polk
Check the prop
I was an outboard mechanic in the late 50s. In those days, props had rubber between the prop hub and the prop to absorb the shock of engaging forward or reverse. Some times the rubber started to slip providing the symptom you described. I don't know how the prop is designed on your motor.
I was an outboard mechanic in the late 50s. In those days, props had rubber between the prop hub and the prop to absorb the shock of engaging forward or reverse. Some times the rubber started to slip providing the symptom you described. I don't know how the prop is designed on your motor.
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Justin - O'day Owners' Web
I bet your shift linkage needs adjustment
Ok - Never played with that particular engine, but here is my guess. First off, have this corrected before you use the engine again or you may destroy your lower unit. For those of us with brand new engines from companies that don't exist anymore, at least not for waranty purposes (read: OMC) this is a big concern. Next, it could be your shear pin. I broke the one on my little 3.3 dink engine and got a similar result to what you describe. The reason was that there was enough pin sticking out to engage the prop at low power but it would slip when more power was applied. I think I had this result because that engine has a plastic prop. Here's what I think is up, though: Your prop is attached to a shaft that ends with a bevel gear in the lower unit. (OK, so it ends with a bearing, let me be simplistic for moment). The drive shaft from the motor has two bevel gears, one with the bevel facing down, and one with bevel facing up. When you throw the shift linkage, you move the drive shaft up or down (there is a splined section that allows this) and one of the bevel gears engages the gear on the prop shaft. Since one will engage from the bottom, and one will engage from the top, depending on which way you shifted, the prop shaft will spin in either forward or reverse, even though the drive shaft is turning in the same direction. for the outboard mechanics out there, I know that there are sometimes more gears in a cage in the lower unit so that its stronger, but this is about right for the little guys. Anyway, if the shift throw is too short, then the gears will not fully engage and they'll slip. This actually tends to happen only in one direction, since what often happens is that the linkage is no longer centered correctly. At low power, the gears engage enough to spin the prop. At higher power, they don't. So - get the service manual for your engine and reset the shift linkage. Or, if you're risk adverse and not a grad student, take it to an outboard mechanic. What ever you do, don't use it again until you fix it, or you may get to see those bevel gears I was talkaing about up close and personal.
Ok - Never played with that particular engine, but here is my guess. First off, have this corrected before you use the engine again or you may destroy your lower unit. For those of us with brand new engines from companies that don't exist anymore, at least not for waranty purposes (read: OMC) this is a big concern. Next, it could be your shear pin. I broke the one on my little 3.3 dink engine and got a similar result to what you describe. The reason was that there was enough pin sticking out to engage the prop at low power but it would slip when more power was applied. I think I had this result because that engine has a plastic prop. Here's what I think is up, though: Your prop is attached to a shaft that ends with a bevel gear in the lower unit. (OK, so it ends with a bearing, let me be simplistic for moment). The drive shaft from the motor has two bevel gears, one with the bevel facing down, and one with bevel facing up. When you throw the shift linkage, you move the drive shaft up or down (there is a splined section that allows this) and one of the bevel gears engages the gear on the prop shaft. Since one will engage from the bottom, and one will engage from the top, depending on which way you shifted, the prop shaft will spin in either forward or reverse, even though the drive shaft is turning in the same direction. for the outboard mechanics out there, I know that there are sometimes more gears in a cage in the lower unit so that its stronger, but this is about right for the little guys. Anyway, if the shift throw is too short, then the gears will not fully engage and they'll slip. This actually tends to happen only in one direction, since what often happens is that the linkage is no longer centered correctly. At low power, the gears engage enough to spin the prop. At higher power, they don't. So - get the service manual for your engine and reset the shift linkage. Or, if you're risk adverse and not a grad student, take it to an outboard mechanic. What ever you do, don't use it again until you fix it, or you may get to see those bevel gears I was talkaing about up close and personal.
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Bob England
Shear pin, too
I once had the same symptoms, and the cause was a broken shear pin. The rubber hub was providing a small amount of friction to turn the prop under low power only.
I once had the same symptoms, and the cause was a broken shear pin. The rubber hub was providing a small amount of friction to turn the prop under low power only.
J
Jon Bastien
Shear pin, part III
I had the same problem with a Tohatsu 3.5 Horsepower outboard. The motor has a plastic prop, and was eating shear pins like they were candy... As it turns out, the first shear pin to break also wore a groove into the prop, and I had to replace the prop as well. With a new prop and pin, I haven't had any more problems. Cost for the new prop was around $35. If you have a plastic prop on your outboard, this is where I'd look first. If not, then the linkage is likely to be your culpit. Good luck! Let us know how it turns out... --Jon Bastien H25 'Adagio'
I had the same problem with a Tohatsu 3.5 Horsepower outboard. The motor has a plastic prop, and was eating shear pins like they were candy... As it turns out, the first shear pin to break also wore a groove into the prop, and I had to replace the prop as well. With a new prop and pin, I haven't had any more problems. Cost for the new prop was around $35. If you have a plastic prop on your outboard, this is where I'd look first. If not, then the linkage is likely to be your culpit. Good luck! Let us know how it turns out... --Jon Bastien H25 'Adagio'
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Walt L.
Hatatsu Thrust Thanks for help
Thanks for the input. I do not think it is gear related because I hear no grinding when I shift and it goes into gear with a solid thunk. It looks like I have a metel three bladed prop. My experience with shear pins is about thirty years old. I suspect that I may have to replace that washer that seems to be giving me some low thrust also. Thanks again
Thanks for the input. I do not think it is gear related because I hear no grinding when I shift and it goes into gear with a solid thunk. It looks like I have a metel three bladed prop. My experience with shear pins is about thirty years old. I suspect that I may have to replace that washer that seems to be giving me some low thrust also. Thanks again
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David
Tohatsu
I think Robert Polk is correct. You probably have a spun hub in the prop. This was a common failure when I worked at a prop shop.
I think Robert Polk is correct. You probably have a spun hub in the prop. This was a common failure when I worked at a prop shop.
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Kevin l. Woody
Slip
Dear Walt, I would have to agree with the respondent who suggested you look at the linkage. Happens frequently with transmissions on inboards. The linkage has possibly worked its way out of adjustment and is allowing the engagement to “pop in or out”. Sorry I’m not more familiar with Outboards. Good luck. Sincerely, Kevin L. Woody
Dear Walt, I would have to agree with the respondent who suggested you look at the linkage. Happens frequently with transmissions on inboards. The linkage has possibly worked its way out of adjustment and is allowing the engagement to “pop in or out”. Sorry I’m not more familiar with Outboards. Good luck. Sincerely, Kevin L. Woody
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Walt L.
Tohatsu Thrust
Thanks for the replies. I think I will start with the prop first and check on the pin / washer. That will give me an answer pretty quick if that doesn't work I will have to go inside. I will be working the boat this weekend and will give you an update monday or so. I most thank I think Jon. The make of the motor is Tohatsu. My apologies for not getting that right.
Thanks for the replies. I think I will start with the prop first and check on the pin / washer. That will give me an answer pretty quick if that doesn't work I will have to go inside. I will be working the boat this weekend and will give you an update monday or so. I most thank I think Jon. The make of the motor is Tohatsu. My apologies for not getting that right.
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