Is My Mercury Prop Spun?

[Phantom309]

1987 Mercury Black Max 150 Xr2 on a 17ft bass boat.
Current prop is a 14 1/4 x 24 II stainless steel 3 blade. Can’t find any marking with a brand or part number on it.

Had it out on the water today, and while running on a plane at WOT, the motor suddenly sounded like it wasn’t under much load anymore and was going faster, while the boat slowed down. I’m almost certain it did not come out of gear. We didn’t hear any noises, and slowed down to idle without taking it out of gear and it continued to move forward. We could go about 6 mph with no issues, before the motor suddenly sounded like it was not under much load and would start to take off, without our speed increasing. Limped back to the dock, thankfully less then a mile away.

I tried to block the prop and spin the shaft with a wrench and couldn’t get it to spin on the shaft. Of course I’m sure the motor is putting much more turning force on it than I did. I’ll post a picture if I can. It looked like there may be some rubber coming out between the prop and hub, near the nut on the shaft. Could he old paint flaking too. But I’m pretty sure it wasn’t there before.
I tried to remove the hub from the prop and it wouldn’t budge even with some really good whacks from a hammer. So maybe it’s a pressed in hub?

Is there anything else I should check other than the prop? I’m hoping that’s all it is, as I was planning to re prop anyway. I feel that it’s over propped. WOT is only 4600 rpm, and top speed 45 mph. Takes a long time to get out of the hole. Im thinking of going to a 21 pitch.

 

[dwco5051]

The short answer is yes. The classic symptoms and visual sign of a spun hub.

 

[RGrew176]

That's usually what happens when you have a spun hub. Happened to me. Fortunately I had twin engines still came home on one engine.

 

[Phantom309]

New prop should be in tomorrow. Fingers crossed.
With my old prop, can it be fixed, or is it worth fixing? It’s a stainless prop and appears in very good shape. I think the pitch is steep for my setup but it was working for me and if it can be easily fixed I’ll keep it as a backup. Any ideas?

 

[dwco5051]

Check with a prop shop. Haven't had one done for years but probably about 1/4 of what a new one costs. It's a good thing to always have a spare even if it not in perfect shape or the ideal pitch.

 

[RGrew176]

The hub can be replaced definitely. I would have it repaired and keep it as a spare.

 

[Texasmark]

New prop should be in tomorrow. Fingers crossed.
With my old prop, can it be fixed, or is it worth fixing? It’s a stainless prop and appears in very good shape. I think the pitch is steep for my setup but it was working for me and if it can be easily fixed I’ll keep it as a backup. Any ideas?

I/m guessing that your gear ratio is 1.76 on that engine. Here is where you are: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

Something isn't right.....way too much slip as you should be up around 55: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

I'd think your prop has been slipping for awhile or your speedometer needs a GPS calibration.

Based on your RPMs, and I would trust them before I'd trust the speedometer, you choice to go to a 21 should give you: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

I find that pretty realistic and yes your hole shot should be much improved.

 

[Sea Rider]

What's the min-max wot rpm range factory stated for that motor ? Let's find out how accurate is a Prop Selector recommending a 21 pitch for that application. Report max wot rpm achieved as loaded..

Happy Boating​

 

[Faztbullet]

Ratio is 2:1....Tex

 

[Phantom309]

I/m guessing that your gear ratio is 1.76 on that engine. Here is where you are: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

Something isn't right.....way too much slip as you should be up around 55: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

I'd think your prop has been slipping for awhile or your speedometer needs a GPS calibration.

Based on your RPMs, and I would trust them before I'd trust the speedometer, you choice to go to a 21 should give you: https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator

I find that pretty realistic and yes your hole shot should be much improved.

Speed was measured with gps on the fish finder, and verified with gps on my phone. Speedometer on the dash isn’t currently working. The tachometer is a cheap one off Amazon and it honestly doesn’t give vibes of being the most accurate. Tach on my dash isn’t working either. It reads about 4x actual rpms. Any ideas on what would make it do that would be appreciated.

 

[Phantom309]

What's the min-max wot rpm range factory stated for that motor ? Let's find out how accurate is a Prop Selector recommending a 21 pitch for that application. Report max wot rpm achieved as loaded..

Happy Boating​

Manual says 5000-5500 for WOT. I got 4600 with my 24 pitch prop and about 650 lbs of passengers and gear.

 

[Phantom309]

Okay guys, so the new prop came in today and I just installed it. It’s a OEM, Mercury Black Max 14 1/4 x 21, aluminum with flo-torq II kit.
Once installed, I gave it a good spin, and in one spot it seems the outside forward edge of the prop is touching the exhaust housing at one point in the rotation. It is just hardly nicking it, so you can barely hear it and it does not slow the prop down. I removed it and you could just see where it had put a mark in the paint on the edge of the prop. The prop appears to be fitting perfectly otherwise. It would seem that something is just a tiny tiny bit out of spec. I went over my installation process several times with the same result.
Anyone had this problem before? My first thought was to just run it, and let it wear the paint away until it isn’t touching. Second thought was use some sandpaper and just touch it up enough to get clearance. Any ideas?

 

[dwco5051]

Look on the back of the tach and there should be an adjustment marked for the number of poles or pulses. If I remember right it should be set at 12 for your motor.

 

[Faztbullet]

Make sure you torque the nut on prop to 55 inch lbs to seat it correctly in hub

 

[Texasmark]

Okay guys, so the new prop came in today and I just installed it. It’s a OEM, Mercury Black Max 14 1/4 x 21, aluminum with flo-torq II kit.
Once installed, I gave it a good spin, and in one spot it seems the outside forward edge of the prop is touching the exhaust housing at one point in the rotation. It is just hardly nicking it, so you can barely hear it and it does not slow the prop down. I removed it and you could just see where it had put a mark in the paint on the edge of the prop. The prop appears to be fitting perfectly otherwise. It would seem that something is just a tiny tiny bit out of spec. I went over my installation process several times with the same result.
Anyone had this problem before? My first thought was to just run it, and let it wear the paint away until it isn’t touching. Second thought was use some sandpaper and just touch it up enough to get clearance. Any ideas?

Other than the binding problem, how did it perform?

 

[Phantom309]

I ended up taking a sander and hitting the edge just enough to take the paint down so it wasn’t binding anymore. Just got back from the river. Performance was great. We didn’t loose any speed, still at 45 but with 800 lbs tho. Holeshot is so much better now. It doesn’t struggle at all or take it’s time, and we didn’t have to move people to the front and it just climbs right out of the hole. Still having tachometer problems but it seemed to be around 5200 at WOT

 

[Phantom309]

Look on the back of the tach and there should be an adjustment marked for the number of poles or pulses. If I remember right it should be set at 12 for your motor.

Mine doesn’t have a setting for 12. I had a hard time finding the right setting, but ended up putting it on 5. It seemed to read fairly close but still was reading a little high.