Prop stops spinning at mid throttle & the engine races

[russee]

Prop stops spinning at mid throttle & the engine races<br />I have a 1964 Evinrud fastwin 18 hp. I’ve been able to figure out and fix many probs over the years but this one has my logic stumped. While going forward at a rather low speed and while turning the throttle up in an effort to go faster the forward propulsion stops and the engine races. The motor bucks a little and over speeds. It stops pushing the boat forward. I drop back on the throttle to a very low speed and I am moving forward again - i.e. the props turning - I try to throttle up again and the same event happens. It’s like a warn clutch is slipping at higher engine revs - but there is no clutch just forward neutral and reverse. I put it in a big tub and try revving it - the prop spins at all engine speeds. So it appears that only under the load of the boat in the water is this happening. I checked to see if the sheer pin sheared by hand spinning the prop while in forward gear. It turns the flywheel and offers compression resistance. So the prop’s sheer pin is ok – right? What’s happening??? - Russ

 

[andys15]

Re: Prop stops spinning at mid throttle & the engine races

The clug dog in the lower unit is either out of adjustment or severely worn.

 

[CATransplant]

Re: Prop stops spinning at mid throttle & the engine races

Yup. Clutch dog. You'll need to replace it.<br /><br />But...here's a safety tip for you:<br /><br />Never turn the engine over with the prop unless you've disabled the ignition. Your outboard uses a magneto system for ignition, and can fire if you turn the flywheel with the propellor. The result could be serious injury to your hand(s).

 

[rwise]

Re: Prop stops spinning at mid throttle & the engine races

russee<br />welcome to iboats!<br />"The motor bucks a little and over speeds" Like it is jumping in and out of gear? Some have had luck with turning the gears and clutch dog around, (use the reverse gear for forward) moving the problem to reverse. For most of us thats not a problem, I don't back up at high speeds I don't know if this will work on your lower unit but may be worth trying.

 

[russee]

Re: Prop stops spinning at mid throttle & the engine races

Thanks for the posts to my problem - It looks like I'm ignorant about what a Clutch dog is. Can you clue me in. Where do I find it (? lower unit?) and what does it look like and what would indicate that its out of adjustment or severely worn. What would indicate it needing replacment And yes for safety I pulled the spark plug wires and ran the gas out before hand turning the prop. Thanks for the wise advice on the safety.

 

[johnshera]

Re: Prop stops spinning at mid throttle & the engine races

I'm having the same problem...<br /><br />Maybe this website will help...On what a cutch dog looks like..<br /><br /> http://www.sterndrive.info/outboardmotor/id1.html

 

[rwise]

Re: Prop stops spinning at mid throttle & the engine races

The pictures in the above link show dog and gears, though yours probably look a little different. the clutch dog is in the lower unit between the forward and reverse gear. over time (and slow shifting) the corners become rounded and it starts to jump in and out of gear. (load clunk or bang with a good jolt). However if it is a smooth slip it could be a spun hub in the prop. If you think this may be the problem, pull the prop and put a mark (with a water proof marker) across the center, hub, and prop. Then put it back on and run it tell it slips, pull the prop and look at the mark. If it does not line up then its a spun hub.<br />hope this helps

 

[russee]

Re: Prop stops spinning at mid throttle & the engine races

Thanks - I now am on my way out to dig into the problem. I currently have 3 potential things to look at. #1 open the side plate on the lower unit to see if the brass shift link rod coupling has loosend up and sliped .This could be the problem if the full stroke of the shift lever isnt transfering its throw to the geers # 2 Check to see if the prop is slipping on the rubber hub (#1 & 2 could life be so easy) and #3 open up the lower unit and look at the clutch dog. I priced the dog at $37 but the forward geer was an unbeliveable $300 for it and the bearing. Thats a deal killer so I hope it's #1 - 2 or just the dogin #3. Isnt the internet a wonder. Thanks all I'll report what I find.

 

[djclark]

Re: Prop stops spinning at mid throttle & the engine races

Please let me know what you find out. I have a 1978 55 HP Johnson with exactly the same symptoms. At low speed she runs great though when I move to anywhere past mid throttle it starts to rev and forward thrust stops. I don't hear any grinding or anything that sounds loose or broken. My problem just manifested this weekend so I have yet to put a lot of time into finding out what is wrong. I will post If I find out anything.<br /><br />Thanks, Doug

 

[Goodoleboy]

Re: Prop stops spinning at mid throttle & the engine races

Hijinx.....you may have a spun prop hub instead of a cluch slipping.<br /><br />When these cluchs slip they sound and feel just like you have hit a log in the water. Itll scare ya half to death.<br /><br />with A spun prop the motor just quickly reves up with no bang or jolt. It will eventualy quit even at low power.

 

[flcorrections19]

Re: Prop stops spinning at mid throttle & the engine races

Well, I HAVE been having the same problem, smooth slip under load and the engine revs up fast and I don't move, But heres the thing, I too was told about the rubber hub failing, so I sent my prop off to be checked and they say the hub is fine. They did say it could be the pitch in my prop as well, in which I thought was a load of crock. You should still have your hub checked its the most easiest way.

 

[flcorrections19]

Re: Prop stops spinning at mid throttle & the engine races

so do we have to get just the clutch dog or the whole dang set of gears 400.00? just wondering.

 

[tunnelwood]

Re: Prop stops spinning at mid throttle & the engine races

I agree with checking the prop hub. it may be spun. I had one that felt tight, but then i tried scratching a mark on it ( from the shaft hole out in a radial pattern). After I ran it again the the mark did not line up anymore. It had shifted from the hub slipping. good luck

 

[the rebel]

Re: Prop stops spinning at mid throttle & the engine races

You are right about the dog engagement making the engine buck and clang inside the foot. It is generally because the shift linkage is misadjusted or the link is loose on the 18 horse. HiJinx on the 55 horse you need to make sure it is going in to gear all the way when you shift it into forward or reverse. I have run into that problem on a 50 before. You can repair it more than one way. Since the clutch dog is cheap buy a new one. The gears can be repaired. I have TIG welded the engagement dogs where they were rounded off from wear, then remachined them on a vertical mill. Afterwards, I draw them back in a draw furnace to retemper them. Or you can just machine the wear off of them and run them with a slightly shorter engagement dog. Both ways will work fine. rwise has a good suggestion also about inverting them, that works too. The main thing to do is make sure the dog is engageing fully when you shift the lever into gear. Hope that helps.<br /><br /> On the prop slippage, I have never had a prop with a slipping hub that would even move the boat after it slipped a hub. What I ran into with my 18 horse Evinrude was a blade shape(cup shape, not pitch) problem. Right before the engine would peak, the prop would cavitate and the boat would loose speed. Back off the throttle and it would pull again until you hit that speed again. The engine would spin up like the hub was slipping. My prop guy told me it was the angle(cup) of the blade, not necessarily the pitch. He put it on his mandrel, wacked it into shape and we tried it again. No more problems. If we could all be that lucky.... BWJ

 

[russee]

Re: Prop stops spinning at mid throttle & the engine races

Here are the results - I went out and opened the side plate on my 18hp and couldnt detect any loose linkage at the conection point. So I moved onto the slipping prop idea. I marked the prop and inner hub as sugested and put the boat back in the water as putting the prop in a tub of water didnt put much resistance on it. Same thing - could go forward slowly but by my reving the engine I had nothing but a racing engine and all forward movement was gone - throtled back and slowed down again but this time I had to go even slower to find the point where the prop would engage. Just one more time I tried to give the throttle a little bit of the gun and the result of that effort was that this time I had to reduce throttle even more to just a hair above idle befor it engaged in forward movement. I was on a river after a big rain and the current was swift. I was glad I went up stream as now there wasnt enough forward movement to go up against the current. I started looking for the canoe paddle. Went straight back to shore. Glad I did. The problem now showed itself with absolute clairity. This time I disconected the plug wires and hand spun the prop. This time there was so much slippage it wouldnt turn the flywheel. I took off the plastic end nut on the prop. A squiggle of rubber fell out - the mark was gone and it was plain to see the center of the prop - the brass or bronze part was standing still and the aluminum prop in my hands was turning. So I'm glad I finaly know what the problem is and have located a prop. Calling around I found prices from 70 to 125 &70 being a slightly used another place new for 80 and another new for 125. I also found a place that specializes in props and does rubber hub replacments for about 50. This is a happy solution as I was aprehensive about breaking into the geers never having done it before. But now I have a prop question - What pitch should the prop be considering I'm using it on a 14 ft aluminum fishing boat? The old prop worked just fine but I dont know what its pitch is and I dont know enough about pitch to know if the 11 pitch of the slightly used one for $75 at the nearest shop is what I should get.??? Thanks for all the information and support. Oh -ya - this link was informative about the clutch dog problem www.marineengine.com/discus/ messages/2/7987.shtml?1062719611 . What I learned in it was to stop shifting in and out of geers gentilly - from now on I will quickly clunk into geer and hopefull avoid future clutch dog problems - I would never had guessed at that logic - clunking into geer was good and gentilly shifting was bad!!!

 

[the rebel]

Re: Prop stops spinning at mid throttle & the engine races

Glad you found the problem and you got back in safe. I run a 10 pitch prop on my 67 Fastwin 18. I have a 14ft. semi V Duracraft which is heavier than your average flat bottom Jon boat. I can use an 11 pitch with out a big load in the boat, but the engine doesn't tach out like it should when the boat is loaded. That is my spare prop. I would recomend the 10. Cabelas has a great price on Michigan props. Check them out. BWJ

 

[russee]

Re: Prop stops spinning at mid throttle & the engine races

Dear andys15,CATransplant, rwise,JohnShera, HiJinx, Goodoleboy, flcorections, Tunnelwood and Big Whits Johnson,<br /><br />Thanks for all the help - got a new prop the same as was on there befor the rubber hub started slipping - a 9 1/4" x 11 pitch. The prop was used at $70 almost new just some paint chips - it was a Michigan brand. I did go to the cabelas site after I bought the new prop and ?I see the price was the same and I learned a lot about props. It looks like I could have used a 9,10, or 11 pitch. The boat planes out nicely when its just me but yes when I have 2 or 3 passengers it takes a while for it to get up and plane and is definatly slower. From what the cabelas prop education page says my 11 pitch will allow me to go faster than with a 10 or 9 pitch. As I mostly have just myself and my wife or one friend I think the 11 pitch will be ok.<br /><br />Again thank you all - the internet is indeed a wonderful thing. I am not a very knowlegable boat person other than with the problems I encounter on my own boat. When I blindly put out a message for help it could be that no one will answer . So the fact that you came to my rescue is great. I imagine that you guys are experienced boat people . I think you are doing a very generous thing spending time on these web sites helping us rookies.<br /><br />Untill I encounter another problem - Thanks - Thanks - Thanks...