Prop moves back and fourth on the pin - normal?

[pretty_amateur]

Hi there,

I was just wondering about my prop be able to move back and fourth along the pin (when I pull it out and push it back in) - about 1/3 of an inch total. It seems like way too much to be moving, yet the nut seems pretty tight. (I didn't try that hard to tighten it though.) Is this normal?

Thanks!

 

[craze1cars]

Re: Prop moves back and fourth on the pin - normal?

Does not sound normal.

However we need to know what year/make/model of motor you are asking about....there have been 100's of ways to retain a prop on a motor over the last century or so...

 

[Texasmark]

Re: Prop moves back and fourth on the pin - normal?

Not sure of your terminology or the problem. In Mercs, at least, you can grasp the prop and push it forward on the shaft at rest.....engine off, shifter in N. The reason for the "slack/slop isn't either. It's caused by the spring loaded shifter and is normal. It is what allows the prop to free spin when you are decelerating whereas you cut the throttle, the boat is settling into the water, but the prop is still in the water, has pitch....it is a screw turning in a "solid medium", and the prop is turning faster than the drive shaft. No biggie.....enjoy your boat.

Mark

Mark

 

[Fed]

Re: Prop moves back and fourth on the pin - normal?

If the prop is moving on the prop shaft then that's no good and you may have a missing or mismatched thrust washer or something.
If it's the whole prop shaft with the end play then that's pretty normal.

Never seen a prop that freewheels when you back off Mark, what are you running there?

 

[jspansel]

Re: Prop moves back and fourth on the pin - normal?

My 5hp merc had lots of free play like that... I just put a new prop on it and actually tightened the nut to spec (8 ft pound), just a hair past hand tight to line up the cotter pin hole and have no play at all. Spins nice and smooth by hand in neutral now.

 

[pretty_amateur]

Re: Prop moves back and fourth on the pin - normal?

Does not sound normal.

However we need to know what year/make/model of motor you are asking about....there have been 100's of ways to retain a prop on a motor over the last century or so...

Hi,

Thanks for the reply.

The motor is a 1970's 20 hp short shaft 2-stroke merc. 4055704 is the serial #.

Thanks (again) for the reply!

 

[pretty_amateur]

Re: Prop moves back and fourth on the pin - normal?

Not sure of your terminology or the problem. In Mercs, at least, you can grasp the prop and push it forward on the shaft at rest.....engine off, shifter in N. The reason for the "slack/slop isn't either. It's caused by the spring loaded shifter and is normal. It is what allows the prop to free spin when you are decelerating whereas you cut the throttle, the boat is settling into the water, but the prop is still in the water, has pitch....it is a screw turning in a "solid medium", and the prop is turning faster than the drive shaft. No biggie.....enjoy your boat.

Mark

Mark

Hi Mark,

Thanks for the reply.

I'm not sure what you mean by not sure of my terminology, but I'll try to explain it again maybe with different words... When the motor is lifted (so obviously not running) I can take my hand and pull out on the prop and push it back in... I'll draw a picture using the "@" symbol as the prop to try to explain better:


<--- @ ---->


So if the prop is level (horizontal) in that picture (as it would be in the water) I can pull (as the arrows show) in a horizontal direction and then push it back in a horizontal direction and it will move about 1/3 of an inch to end to end.

I wouldn't think this is normal - but then again I don't really know.

Thanks (again) Mark for the reply!

 

[pretty_amateur]

Re: Prop moves back and fourth on the pin - normal?

If the prop is moving on the prop shaft then that's no good and you may have a missing or mismatched thrust washer or something.
If it's the whole prop shaft with the end play then that's pretty normal.

Never seen a prop that freewheels when you back off Mark, what are you running there?

Hi,

Thanks for the reply.

The whole thing moves. The prop and nut, washer (everything in the center of the prop) all moves with it. I just figured it would feel like it's solid in one place and not move fwd and backwards at all. I've never felt that on any other prop.

Thanks (again) for the reply!

 

[pretty_amateur]

Re: Prop moves back and fourth on the pin - normal?

My 5hp merc had lots of free play like that... I just put a new prop on it and actually tightened the nut to spec (8 ft pound), just a hair past hand tight to line up the cotter pin hole and have no play at all. Spins nice and smooth by hand in neutral now.

Hi,

Thanks for the reply.

Oh, what do you mean by "hand tight"? I think I know, but just to be sure. I will be putting a new prop on and should know exactly what I'm doing. I'm guessing you mean, using a ratchet or whatever you would use (what did you use by the way?) I should tighten it as tight as I can without really heaving on it. Just enough so it should spin nice 'n smooth, and be tight.

So were you saying your 5 hp does the same thing as my 20 though - with the back 'n forth movement?

Thanks (again) for the reply!

 

[Texasmark]

Re: Prop moves back and fourth on the pin - normal?

Easily answered. With the engine off, put your shifter in F gear. Grasp a blade of the prop and attempt to turn it cw and ccw. One way you have to turn the engine over to get the prop/propshaft to turn. The other direction the prop turns freely making a clicking noise about every 10 degrees and if you watch the distance the prop is from the lower unit housing, you will notice it move back and forth. If you ever took a lower unit apart and looked at the rear of F gear you would see what and I told you why.

Mark

 

[Texasmark]

Re: Prop moves back and fourth on the pin - normal?

What I'm talking about is not free play. It's the way the lower unit functions and the prop is torqued to 55 FT lbs. It's 90 hp and runs a 17' bass boat at better than 50 mph gps. Can't hardly have a problem and do that!!!!!!!!!!!!!!

 

[Texasmark]

Re: Prop moves back and fourth on the pin - normal?

If the prop is moving on the prop shaft then that's no good and you may have a missing or mismatched thrust washer or something.
If it's the whole prop shaft with the end play then that's pretty normal.

Never seen a prop that freewheels when you back off Mark, what are you running there?

The prop is not moving on the propshaft!!!!!!!!!!!!!!!!!!!!! The prop shaft is what's turning with respect to the drive shaft!!!!!!!!!!!!!!!!!! Get yourself a manual on engines and look in the lower unit section. May be an educational opportunity!!!!!!!!!!!!!

 

[Fed]

Re: Prop moves back and fourth on the pin - normal?

pretty_amateur disregard Texasmark's post #11 as it was aimed at me, your prop nut torque spec will be much less than Mark's 90HP 55 Ft/Lbs.

Mark, RELAX!!!!!!!!!!!!!!!!!
I'll be back after I get the Sunday papers.

 

[Fed]

Re: Prop moves back and fourth on the pin - normal?

OK I'm back.

The prop is not moving on the propshaft!!!!!!!!!!!!!!!!!!!!!

We didn't know that until post #8.

The prop shaft is what's turning with respect to the drive shaft!!!!!!!!!!!!!!!!!!

I have no idea where this fits into the OP's question?

Again, I have never seen a prop that freewheels when you back off, at least I've never heard any of my Mercs ratcheting but maybe they do.
It was just a simple question Mark, do you get it!!!!!!!!!!!!!!!!!!!!