Lost propulsion

[donnyk]

I have a 2008 Tohatsu 9.8 Four Stroke.
Coming down the lake the prop suddenly lost propulsion.

I have had it apart. Gears and everything all look great. It appears that the clutch is not engaging fully in Forward. reverse is fine.

Is there a way to adjust the clutch?
Could this be a linkage problem?

Any ideas?

Thanks,
donnyk

 

[Texasmark]

Re: Lost propulsion

Have you hit something lately with your prop? Unless you have been messing with your engine lately no reason for linkage to just go whacko, especially when you are at WOT and not doing anything.

Put the engine in a vertical position with the cowl off. Shift to F gear. Stand on the left side of the prop and watch the crankshaft. If the prop turns with your weight on it and the crankshaft doesn't your slip clutch in the prop is bad. Rehub or better new prop time. If the crankshaft turns proportional to the prop you have something else.

That is a quality engine and only 5 years old. Unless you have severely abused it, no reason for an engine mechanical failure.

Mark

 

[donnyk]

Re: Lost propulsion

Have you hit something lately with your prop? Unless you have been messing with your engine lately no reason for linkage to just go whacko, especially when you are at WOT and not doing anything.

Put the engine in a vertical position with the cowl off. Shift to F gear. Stand on the left side of the prop and watch the crankshaft. If the prop turns with your weight on it and the crankshaft doesn't your slip clutch in the prop is bad. Rehub or better new prop time. If the crankshaft turns proportional to the prop you have something else.

That is a quality engine and only 5 years old. Unless you have severely abused it, no reason for an engine mechanical failure.

Mark

Would the prop be bad if reverse is ok? Just does it in Forward.

 

[steelespike]

Re: Lost propulsion

A motor will lose propulsion if you pick up a pack of weeds or a plastic bag or some other trash in the water.
If it simply revved while it loses propulsion it very likely is a spun hub.
You can check by removing the prop and drawing a water proof line across the hub and housing.
Run the boat and check the line.
It has a clutch dog not like a car clutch. The clutch and gears have lugs on them that engage to drive the prop.
If the dog was bad it would clunk like you hit something and wouldn't really rev much.
The gears are in mesh with the drive shaft all the time and free on the prop shaft. The clutch is in between the gears and splined to the prop shaft. It slides to engage the gears thus causing the prop to go forward or back.
The dogs are what makes the crunch as you shift.
It is advisable to shift crisply, neither dragging it into gear nor jamming it in .
Best to try to shift at idle speed to prolong the life of the clutch and gears.

 

[Texasmark]

Re: Lost propulsion

Would the prop be bad if reverse is ok? Just does it in Forward.

I'm going to say yes it could. Reason is you don't use a lot of thrust in reverse. Additionally, the way the hub is slipping, may catch in the reverse direction; like fingers laid back in the slipping direction but the points of the fingers are there to dig into the hub when reversing.

Check the prop.

Mark

 

[Sea Rider]

Re: Lost propulsion

Make a hub slip test to see if you have a spun prop, or lend yourself one and test. If fine, buy a new one.

Happy Boating

 

[Okieboatguy]

Re: Lost propulsion

Last summer at WOT, I would loose all power. However if I throttled to below 2200 rpm, after coming out of neutral, I would have thrust, until I hit the magic 2300 rpm. I excluded the prop off the bat since it was a brand new Merc. Quick Silver, with less than 4 hours on it.
Through testing once I got it back to the marina, I verified it by checking compression and so forth, with no problem found. I then took it back out and found the issue disappeared completely, I would hit WOT on several hole shot starts with no issue, until I tried it the 5th or 6th time, then it lost power. Through investigation I found that the prop would slip, only when I would throw it up to WOT, and then run it there for 2-3 minutes. I verified that was the issue since I had placed a mark on the hub and the prop earlier during troubleshooting, and once I was back in I found that they had moved apart from each other.
Check the prop again, no matter how new, or how it looks, it could still be spun.