Prop Hub Spun or Other?

[Toyman991]

I have a 1962 28hp Johnson RX-10 on the back of my 1957 Cadillac Daytona. It's a bit on the thirsty side but has proved to be nearly buletproof. Yesterday I took it out for a spin on the lake and after several miles at top speed, the engine revs picked up and the boat slowed. I did not feel the clunk that I have always thought jumping out of gear would produce but I don't know what that feels like.<br /><br />The prop is the pin-drive style that came with the motor when I got it. Do these have a rubber hub that can spin? Could the motor have jumped out of gear without a clunk? When I backed off the revs, forward push resumed. Also, when I went to idle and shifted to neutral, reverse and then forward, everything felt fine. <br /><br />I have not changed anything recently except the lower lube (with Mercury Premium rather than the Lubrimatic I normally use). It seemed somewhat thicker but it did say for use with all outboards. Could this be the cause? Have never had cavitation with this boat so I don't think this is it although this is what it felt like.<br /><br />One more thing, I pulled the lower unit a couple of weeks ago just to make sure it wasn't stuck to the leg and when I reconnected the upper and lower shift rods is it possible that I did not do it right? I normally push the lower rod all the way down and shift the handle so that the coupler is also all the way down when I join and secure them. My Clymer is vague on this point...am I doing this wrong? Is this the cause of my current problem?<br /><br />Sorry for the long post but I wanted to include as much information as possible. Thanks for your help, John

 

[Silvertip]

Re: Prop Hub Spun or Other?

Pin drives don't have a rubber hub. They have a shear pin (the pin drive). With the engine off, put the engine in gear and try to turn the prop by hand. If it spins without turning the engine over, its either not in gear, or you need to remove the prop and replace the shear pin. Check the pin seating area in the prop. Through many cycles of speeding up and slowing down, the pin hole in the prop shaft or the area where the pin seats in the prop can be deformed (becomes a sloppy fit). This gets progressively worse to the point where the shear pin can't stand the rocking forces any longer. The fix is to replace the prop (if theat's were the wear is) or repair/replace the prop shaft.

 

[BoatBuoy]

Re: Prop Hub Spun or Other?

According to Paul Moir, all props have rubber bushings since the '40's, pin or not. Do the "spun prop" test. With a Sharpie or other, mark a line across the inner hub and prop. Force it to exhibit the described symptoms. Then remove and examine your mark. If spun, the marks won't be aligned like the were when you made the mark.

 

[cajun555]

Re: Prop Hub Spun or Other?

Toyman, Yes indeed, even if it is pin drive it does have a hub. Its a brass insert pressed in the aluminum prop with a rubber hub. I've got a 56 30 hp, 62 28 hp and a 63 40 hp. All have pin drives and pressed in hubs.<br /><br />The easiest way to tell if your hub is slipping is pull prop and put a mark on the brass and alu. Test out in water and pull prop to see if the marks still align up.

 

[Toyman991]

Re: Prop Hub Spun or Other?

Thanks all. As soon as this FL rain stops I'm going to mark my hub/prop and take the boat out. I picked up a spare prop a while ago so I can swap it out if that proves to be the problem. Is it a big deal to have a new hub pressed in?

 

[OBJ]

Re: Prop Hub Spun or Other?

No big deal Toyman....take it to a prop shop and they should be able to rehub it for ya'.

 

[bubbakat]

Re: Prop Hub Spun or Other?

If the prop is in good shape it is well worth it.<br />I have had two done this year.<br />If you need a good place to send it just post it here and i'll post an addy for you. The man does good work and very honest.

 

[Toyman991]

Re: Prop Hub Spun or Other?

Thanks Bubbakat. I'm going out tomorrow regardless of the weather since I need to pull the boat out of the water and put it back into the shed. I'll post my findings tomorrow after I test for a spun prop. John

 

[BillP]

Re: Prop Hub Spun or Other?

Hey Toyman911,<br />How about posting a pic of your classic? I like old boats and pics are always fun.<br /><br />Bill P.

 

[Toyman991]

Re: Prop Hub Spun or Other?

Good Morning,<br /><br />I marked my hob/prop this morning and went out on the lake (lake Beresford on the St Johns for you fellow Floridians). When I felt the slipping, I came back in to the dock and pulled the prop. Well...the marks still line up! Either they spun around and lined back up, which is extremely unlikely, or I have a different problem. Any other ideas? If it helps, it feels and sounds just like cavitation which has never happened to me in this boat before. Please help. <br /><br />P.S I'll post a pic as soon as I figure out how.

 

[DHPMARINE]

Re: Prop Hub Spun or Other?

You have checked the drivepin?Only other idea right now is check shift rod connector,make sure the bolt goes thru the groove portion of the shift rod.<br /><br />DHP

 

[Toyman991]

Re: Prop Hub Spun or Other?

I checked the linkage and found that the lower rod was a hair high in the connector. I lowered it about 1-2mm but it's hard to tell wether it's in the groove or not since the connector obstructs my view of the groove. If the lower rod was set too high in the connector, wouldn't this favor the forward shifting of the L/U? Could the gearcase somehow go beyond forward gear into some sort of neutral again?<br /><br />Anyway, I took the boat out for about 15 minutes of full and near-full throttle running and the problem did not recur Perhaps this small adjustment fixed it? I just don't think so because I have always thought popping out of gear would feel more abrupt than what I felt. Also, backing off the throttle seemed to "hook it back up". This sounds to me more like cavitation which, as I have said, has never happened in this setup before.<br /><br />BTW, don't you just love working with small motor parts while the boat is still in the water? John

 

[DHPMARINE]

Re: Prop Hub Spun or Other?

Toyman991, lets hope that was the problem,and no real damage was done.These older motors are worn,and sometimes need tweaking a bit.When I reinstall a gearcase,I visually check thru the bolt hole that the lineup is good.<br />GoodLuck,<br /><br />DHP

 

[Solittle]

Re: Prop Hub Spun or Other?

At this point Toyman I think you are on the right track to pursue the possibility of cavitation. Where is the cavitation plate relative to the bottom of the hull?

 

[Paul Moir]

Re: Prop Hub Spun or Other?

There's really no way for the lower unit to allow the engine to spin independant of the prop without making loud mechanical complaints. If the clutch dog was slipping due to a mechanical problem in the shift linkage or simply wear, you'll get a massive banging from the engine - much like hitting a log repeatedly. It's possible that the splines in the crankshaft where it meets the driveshaft stripped, but again there would be horrible mechanical noises occuring whenever it started slipping. That might be worth investigating though.<br />If you have your shift linkage adjusted to push too far into forward, the clutch dog cradle will wear faster, but you won't enter neutral again. It's impossible.<br />The lower unit shift rod connector is not supposed to be adjustable in any way. Rather all adjustments are to be made at the shift handle itself.<br /><br />If you're certain you don't have a slipping hub, I think the only answer can be cavitation like SoLittle said. It's strange that it would come up all of a sudden though.<br /><br />Tell us what you find!

 

[Toyman991]

Re: Prop Hub Spun or Other?

Sorry for the delay in getting back to you kind folks. I left the boat in my dad's shed and now I'm back in Tampa. To answer a question that was posed, the cavitation plate is essentially flush with the bottom of the boat at the transom. It may be an inch lower, if at all. While the symptoms sure do feel just like cavitation, why would it start now? I've owned this boat and motor for nearly four years and haven't changed a thing. Very puzzling.<br /><br />Anyway, is there a surefire way to rule out cavitation? It only seems to happen at top speed which is about 26-27 mph according to my eTrex GPS.<br /><br />I'll post a picture to the board as soon as I figure out how. For those of you who attend the Mt. Dora show each March, I usually beach my boat next to the Feathercrafts since it is so much easier to zip across Lake Dora than fight the parking crowds. John