Lower end 'slipping'?

[tnltracy]

I've noticed a few times when I rev up to WOT, my motor will seem to rev up as if the prop has lost traction, or is slipping. My best description is like a tire spinning in a car. The motor revs up, but there's little to no forward thrust.

I'm wondering if the prop is somehow getting 'airlocked', or if I possibly have a larger issue with slippage somewhere in the lower end.

Thoughts?

 

[Xcusme]

Re: Lower end 'slipping'?

Your description could be from 2 things. The prop is cavitating , catching air or you have a spun prop hub. Remove prop, mark inner and outer hub with grease pencil. Replace prop and take to WOT on the water. After she slips again, remove prop and see if your 'line' has moved. If the line isn't lined up, you have a spun prop hub, get prop re-hubed.

 

[billybowlegs]

Re: Lower end 'slipping'?

The exact same thing happened to me for the first time this morning!! I have an Evinrude E-TEC 115hp outboard with only about 40 hrs on the motor which I purchased new.

Motor started right up, went for about a 15 min run at 3/4 speed, slowed to idle speed while in a harbor for about 10 min, then on the way out, increased throttle and boat RPM's went to about 3000 but no significant power. Not enough to get on plane and only slightly faster than idle speed. Cut motor off and raised to see if anything in prop. Nothing noted. Restarted motor without problem, tried again and same thing. No alarms, no warning lights, good water flow through engine. Idled toward home, and after 5 min. tried again and we were off at normal speeds, no problem. Got home and checked prop....seemed tight, nothing wrapped around shaft. Plenty of oil.....only other thought I had was that engine went into SAFE mode but no alarms, no warning lights???

Any thoughts??

Bryan

 

[5150abf]

Re: Lower end 'slipping'?

The lower can't "slip" ,the drive shaft is splined to the power head and the lower itself is always turning and the gears are splined to the prop shaft so it has to be something with the prop, either the hub is spun or it is cavitating.

are you sure the motor was trimmed down, sometimes on mine if you forget to trim it down after running sped the prop will grab some air until you trim it down OR you motor is set too high on the transom which makes trimm even more critical, one of these should be your problem, check for spun hub first.

 

[tnltracy]

Re: Lower end 'slipping'?

I should have stated that the motor is a 1958 Johnson 35. no power trim, so motor is down. Also, the prop sits on a pin through the shaft, so no way it's going to slip on the shaft unless the pin were to snap which it isn't.

So my guess is that it's cavitating. Interesting thing is I'm confident trim angle is good, and the motor actually sits a couple inches lower than optimal, so odd overall that this would be happening. Maybe just the shape of the boat, also a 1958 aluminum is just feeding it some air at the right speed. Once I figure out the carb issues (separate active thread), I'll get a co-pilot to see if I can get any kind of visual on it.

 

[CATransplant]

Re: Lower end 'slipping'?

Like most, your 1958 Johnson has a rubber hub in the prop. You can't see it, but it's there. Given what you describe, it's almost certain that it's slipping. Nothing else in the drive line can slip like that, and, unless your outboard is mounted way, way, too high, it isn't cavitating.

Try a spare prop or take the old one in and get it rebuilt. Props for that engine are inexpensive, and there are always dozens of them for sale on ebay. Buy two. Always have a spare.

I had your exact engine. I guarantee that your problem is a slipped hub. Get a good prop and it'll be fixed. Happens all the time with those props, especially the 50-year-old ones. Rubber deteriorates.

You can get a brand new prop for that outboard right here on iboats. You'll be surprised at how inexpensive they are. I bought my spare prop, though, on ebay. Cost me $15, plus shipping.

As long as your anti-ventilation plate on that engine is running underwater, it's almost impossible to get that 35hp to cavitate the prop. The engine is designed to run a bit deeper than most modern engines.

Don't waste any more time trying to figure it out. You have a slipped hub.

 

[tnltracy]

Re: Lower end 'slipping'?

Well, how about that! I have the original 25lb brass prop on there, but didn't know that. I'll get another as you suggest and hopefully resolve the problem.

 

[Shizzy]

Re: Lower end 'slipping'?

I have the same issue on my 6HP Johnson (1965) it seems worse after running the engine for some time. I also get an odd noise at times (kind of a loose bearing sound) when I am at about 3/4 throttle. Spun Hub for me as well?

 

[wilde1j]

Re: Lower end 'slipping'?

Shizzy, see above Xcusme post.

 

[tnltracy]

Re: Lower end 'slipping'?

New (to me) prop on the way and will be mounted this weekend. Took it out last weekend and after a bit of running, could not get over 1/2 throttle without it slipping.

What's best way to find someone to rebuild my original prop? Or given the insight into cost to buy new (mine's coming for less than $50 shipped), is it easier to just convert it to a paperweight and buy another for a spare?

 

[Chinewalker]

Re: Lower end 'slipping'?

tnltracy,
Also, I would not use the bronze prop! They look neat all shined up, but they put a lot of strain on 50 year old clutch, gears and shafts. I find clutch dogs wear out much faster with the heavy bronze wheels, and considering the cost of new dogs (if you can find them at all), it's a no brainer. Find an aluminum of the same pitch and diameter and keep the bronze for show...
- Scott

 

[wilde1j]

Re: Lower end 'slipping'?

Assuming it is slipping (you marked and checked it, right?), look in the yellow pages for propeller repair and call and ask the cost to rehub.

 

[F_R]

Re: Lower end 'slipping'?

It was suggested several times to mark the hub, but nowhere do I see that you have done it. It isn't too bright to replace it before even knowing if it is bad. Sorry 'bout coming on so strong. You don't even have to remove it to mark it. Just draw a line between the prop nut and the propeller itself. If it spins the nut will turn with the shaft within the propeller and will no longer align.

 

[tnltracy]

Re: Lower end 'slipping'?

You are right, but given the symptoms, and the fact that I didn't have a spare anyway, I needed a new prop. Got a pretty inexpensive aluminum one from eBay and tried it out yesterday. Definatly was the solution. I think I"ll find somewhere to mount the brass prop for decoration and find myself another aluminum one as a spare now.