prop slipping?

I have a 1975 Mercury 650 O/B. It is on a 1975 14.5' Sportcraft Runabout (no poer trim or tilt). I just replaced (what i think was) the original prop. I replaced the prop because the hub was "slipping". I could idle out fine, but when i hit the gas, the boat moved just as slowly, but the engine was full throttle. When I pulled the old prop, the old thrust washer (nearest the gearbox) was "very shiny" and the serial numbers on the prop were rubbed off. The mechanic at the marine shop in town said that the hub went bad.<br /><br />OK, here is the new problem. I put a new prop (Comprop) on and took it out to the lake with the kids. My son was driving and I was kicking back, relaxing. All of the sudden, I saw the motor pull out from the boat about 6 inches, then drop back down. The motor was running the same speed (rpm) but it felt like the boat was not moving as fast. I thought maybe we hit something under the water, but we pulled into a cove and I pulled the motor up and looked at the prop. No dings, no scratches, no sign of contact. I pulled the prop off and noticed that the gearbox end of the prop was scratched (inside and outside). If you don't know about Comprops, they are composite props that look as if they are plastic, but are as strong and durable as aluminum. It appeared to be rubbing against the gearbox housing. The thrust washer moves with the prop.<br /><br />Here's something else. When I installed the new prop the lock washer fit snug against the propeller and I screwed the lock nut on tight. When I pulled the motor up today, there was a 1/2" gap between the lock washer and the front of the prop hub. The lock nut does not fit past the threads (does not fit over the splines), so it is not like the nut backed out or anything. The lock nut is tight to the end of the thread on the prop shaft. The prop itself slides up and down the shaft that 1/2". Is this normal? <br /><br />1) Should I get another thrust washer, since the old one is obviously worn? <br />2) Should the prop have play in it on the shaft? <br />3) Should there be wear on the gearbox side of the prop? <br />4) Is there supposed to be anything between the prop and the gearbox housing? (grease, seal, bearing, etc)<br /><br />Please reply if you can answer any of these questions. I don't want to ruin this "fixer-upper"

Re: prop slipping?

sounds like a lower unit rebuild, to me.

Re: prop slipping?

sorry

Re: prop slipping?

Maybe that prop requires another type of thrust washer?<br /><br />If you still have your old prop, try to fit it again and see if you encounter the same problem. I mean, prop loose with locknot all the way in.<br /><br />Just as a side note, when you tighten the prop, you don't need to make the nut superman-tight. It's a nyloc and you have a crown plate to keep from going loose.

Re: prop slipping?

hmm... is there supposed to be play in the prop? on the shaft, i mean. And is there supposed to be something that seperates the prop from the gearbox housing?

Re: prop slipping?

is it possible you have the wrong prop. diagram just show thrust washer behind prop. the flange on the gear box side of the prop,protruding farther than the old prop, and you thought it was on tight because it was hitting. take some maesurements and compare the to props.

Re: prop slipping?

"hmm... is there supposed to be play in the prop? on the shaft, i mean. And is there supposed to be something that seperates the prop from the gearbox housing?"<br /><br />Yes, it's the thrust washer the guys were talking about. It slides over the shaft and has a chamfer on it forcing it to go on only one way if you pay attention and line up the chamfer with the chamfer on the shaft.<br /><br /> I have noticed that some props (for sale) indicate that they take a different thrust washer than other props.....and they supply you with the number. I don't know why, but I do recall that where I saw it was in the Merc section (Michigan Wheel charts I think) and the prop was aluminum.<br /><br />Also on the nut, the nut has to be tight; like my manual says 55# and they mean 55#, which I learn last week. So now you have the prop sandwiched between the thrust washer and the nut/locking disc. Nice and tight. There could be a little slack between the prop shaft and the lower unit (gear lash) but none between the prop shaft and the prop.<br /><br />The prop then can turn freely without striking the lower unit.<br /><br />Mark

Re: prop slipping?

ok, so I took a look at the gearbox "flange" and the prop. there is a 3mm gap between the prop and the housing. The prop turns freely. the measurements inside the two props are the same and the thrust washer fits. I just do not understand why there is scarring on the inside of the prop; it doesn't have anything to rub against... when you put it in gear, does the prop shaft move in and out? are the gears in the housing rubbing the inside of the prop maybe? forgive me, I only know enough of this stuff to get me in trouble. I do appreciate the help though.

Re: prop slipping?

I am on the other side of "expert", but I do have the 72 650 and have read every message on here even remotely related to it. If I recall what I have read correctly, the prop shaft does move inward (I don't remember how much) when reverse is engaged, in order to allow the appropriate gears to align.<br /><br />E

Re: prop slipping?

Yes it does move in slightly; looks like a lot but it's only about 1/16 inch (62 thousandth's) when you measure it. You can push in on the prop with the engine stopped, like sitting on the trailer out of the water, in N or F makes no difference. The prop is not (should not be moving), the shaft is.<br /><br />Mark

Re: prop slipping?

thank you for the input. I'm new to this myself. I do know that I can slipe the prop on the shaft about the 1/2" described above, it's not the shaft moving. What I guess i need to know is if I need to get a spacer washer to kill the gap and seperate it more from the gearbox. it seems to be rubbing and scarring up the inside of the prop on the gearbox side. is thee supposed to be a bearing around the inside of the gearbox housing and the guy who owned it before lost it or took it out? At the moment, it's just metal. also if the gap is filled, will it hurt the motor, prop or performance of the engine. Thanks for the help guys, i appreciate it.

Re: prop slipping?

Im not an expert. But NO the prop should not slide up and down the prop shaft with the correct thrust washer and the lock nut tight.Like (Texasmark)said compaire the old prop to the new one see if there is a difference. The comprop could take a different thrust washer.The only thing behind my prop is the thrust washer. The only other thing I could think of would be that maybe you did hit something and the hub on the comprop has sliped. Good luck hope I helped a little.

Re: prop slipping?

thank you BMW for the answer for the prop slide. I appreciate it. It can't be the hub on the comprop, because there is no hub.<br /><br />anyone know why the motor came out of the water without a strike? it came up about 6 inches, then went back down. it never came out of the wate, but i thought that it was going to fall in may lap for a second there

Re: prop slipping?

BMW II. What I said was that the shaft moves; the prop is rigidly affixed to the shaft. <br /><br />In reading my manual it seems that this is normal, but I am currently investigating. I totally agree with anyone who wants to agree that the prop should never be loose on the shaft.<br /><br />And rojsan, I would not add any washers to the OEM thurst washer. Again, my book says that the prop nut is to be torqued to 55 ft#.....that's tight and the nut is pushing the prop against the thrust washer in developing this torque.<br /><br />You can (I can) push my shaft in slightly, but when pushed in, rotating the prop causes no friction, noise, or interference of any kind.<br /><br />Mark

Re: prop slipping?

The motor probably kicked up because the actuators on the motor are worn or broken. Either that or it was never properly locked down. What kind of waterway were you running in? If it was a soft mud or sandy bottom, you may not have any visible damage to the skeg, lower unit or prop. When you throttle up in reverse does the motor raise up? A good solution for a broken or worn out manual tilt is an aftermarket trim/tilt setup. It is often less expensive than the original manual tilt repair.

Re: prop slipping?

OK, lets not lose sight of the original post. Sorry (Texasmark) I confused(Tashasdaddy)reply and yours.But I do understand what you are saying.(Rojsan)to answer your 4 original questions. 1)Yes, it might be a good idea to get a new thrust washer.Dont know how much they are $$$$ but cant be to expensive.2)NO,the prop should not move up and down the prop shaft,with the correct thrust washer and the lock nut tightened down all the way.3)NO, there sould not be wear on the gear box side of the prop.4)YES,there is some thing between the prop and gear box.(THRUST WASHER)that is all i see on mine.The comprop has to have some kind of hub on it.To keep the shaft from spinning in side the prop.If you cant see any damage to splined part (inside of prop)and you can see 1/2 in.of shaft on either end then I think the thrust washer is bad or not the correct one for the comprop.I hope this is of some help to you.Good luck.

Re: prop slipping?

thank you for your input studly, and thanks BMW II for answering my original questions. I've learned a great deal from this post. I have ordered another thrust washer and hopefully it takes out the slack in the prop. <br /><br />Studly, the comment about the actuator- what is that? is it in the motor, the lower unit or the mount? <br /><br />BMW, to clarify the hub issue. A comprop is designed to break away in case of prop strike, so the blades and center are all the same piece- it's molded "plastic" (composite material). It's not like an aluminum prop that has the rubber inside to allow it to spin in case of strike.<br /><br />I'm sorry for the ongoing questions. I'm just trying to learn everything I can about this thing so I don't get my family stranded in the middle of the lake <br /><br />Tex, this is what I am talking about the prop hitting the gearbox. The circumference of the prop, inside and outside seems to be rubbing the inside and outside of the gearbox, causing scarring on the outside and inside of the prop (gearbox side). Imagine taking your finger and running it around the inside of the prop. That is the puzzle, because there is a 3mm gap between the gearbox housing and the prop. neither one touch each other. Am I making any sense?