# Another Mercury 15HP problem



## kbkid (Sep 20, 2009)

After finally getting my 1988 Mercury 15HP running last weekend, I took it out today for its first real test for today. 

Two things I noticed were it takes a while for the motor to run before I can take the choke off. This may be due to the temperatures and/or previous usage. Regardless, this wasn't that big of a deal.

The second problem was after running it for a solid 25-30 minutes at varying speeds, I went to accelerate once more and the motor itself seemed to rev but the propeller didn't seem to spin with the same amount. I immediately took it down to idle. Next I tried to accelerate again and it did the same thing. 

The propeller would spin and I was able to still move at a low RPM/speed. 

I've read online and from what I've found, it sounds like the propeller hub is slipping or spinning. 

What do you think from what I've described?


----------



## crazymanme2 (Sep 21, 2009)

Yes I agree with your conclusion.As far as the motor taking a long time to warm up 2 things, first make sure your thermostat is working & second make sure your carb is adjusted right.Could be a little lean


----------



## Captain Ahab (Sep 21, 2009)

Easy way to see if your hub is spun is to place teh motor in gear (while on the trailer and not running) and see if you can turn the prop by hand - if you can get it to move - spun hub. 


Lucky for you this is an easy fix - just remove the prop, pound out the old hard rubber hub and place in the new one.

BTW - you should always carry a spare hub with you - just in case you hit something and spin it while on the water


----------



## kbkid (Sep 21, 2009)

Captain Ahab and crazymanme2, thank both of you guys for the help.

Any recommendations on where to get a new propeller and or new rubber hub?


----------



## CarlF (Sep 21, 2009)

Google boat propellers and you will get a ton of sites. 
Shop around, you will find that prices vary alot as does shipping.


----------



## kbkid (Sep 21, 2009)

I guess I need to first figure out which part needs to be replaced.

As far as I can tell, this is the exploded view of my motor's prop shaft:







Which part number are you guys referring to that needs to be replaced?


----------



## Captain Ahab (Sep 21, 2009)

The part number is not there - you need to replace the hub


----------



## kbkid (Sep 21, 2009)

Interesting. This is the exploded view of my engine apparently, based on the serial number I provided.

The only other option they provided was a second propeller design. It looks like this:






But still, by judging what you posted Captain Ahab, it doesn't look like that is the correct image either.


----------



## kbkid (Sep 21, 2009)

Also, it seems as though the rubber hub is now obsolete technology. 

The reason I say this is because of the Mercury Flo-Torq hub kit. It apparently replaced the older rubber hub from what I've read.


----------



## kbkid (Sep 21, 2009)

I've also been reading through the Service Manuals that Jim had available. In the manual, they it states there were four different lower unit configurations. I've got the four, narrowed down to two different ones. Here are the exploded views from the two:











I'm unsure which is exactly what I have. Regardless, neither have the object you posted Capt. Ahab.


----------



## huntinfool (Sep 21, 2009)

The hub is in the propeller. You can get another prop or have that one rebuilt. There are several places around here that do them, but not familiar with your area, but an internet search should find one near you. I would also consider getting a spare and the tool to take it off. 

I saw on tv one time a gadget that you could buy to put on your prop if you had spun the hub and it would get you back to the launch. I can't remember the name and I don't know if they came in different sizes or not. But thinking about it, it sure was a good idea.


----------



## kbkid (Sep 21, 2009)

Thats the impressions I was under as well. I thought the hub came with the propeller, or I could take it to a shop and they could fix and/or replace the old rubber hub.

I'll have to check some prices for a new prop then. 

Thanks for the heads up everyone.


----------



## kbkid (Sep 28, 2009)

After a week of searching for props, I have a few questions now.

On some websites, they list multiple props which vary in pitch that fit my engine. 

What I have is a 9" prop with a 10.5 pitch. As far as I can tell, the hub is spun. 

My question is, how do I make sure this is the correct prop that should be on the engine to begin with. What are the consequences of running a prop with a higher or lower pitch? 

What I mean is, the prop I have apparently has a spun hub. Was it due to it being the wrong prop to begin with and the RPMs getting too high?


----------



## CarlF (Sep 28, 2009)

Usually a prop spins the hub because you hit something or just simply wears out. 
I would guess that the diameter and pitch you have will work fine, just buy another one just like it.
Unless you have a tachometer to check rpms, messing around with changing the pitch is a crap shoot.


----------



## kbkid (Sep 28, 2009)

Thats why I ask. I just wanted to double check that the prop I have now is really the correct one that should be on it.

The hub that is in it now looks pretty worn. I will probably just pick up the exact one but I wanted to check.


----------



## kbkid (Sep 28, 2009)

It turns out that I ended up calling Mercury Marine today. I gave the guy my serial number and he was able to tell me everything about the engine.

Apparently, the propeller that originally came on the engine was a 9"x9". What I pulled off of it was a 9"x10.5".

He recommended that I stick with what came on it from the factory, but assured me that no major damage could be done by the previous owner running a 10.5".

I also asked about replacing the rubber hub, as Captain Ahab suggested. He told me that with the late '80s models, the entire prop needs to be replaced once the hub goes out. He said some companies have took it upon them to reproduce the rubber hub and to replace them, but said they normally don't warrant the new hub or work done.

I called a few local Marine shops around me and asked about getting a rubber hub replaced. Two dealers told me they wouldn't touch doing it. They suggested buying a whole new propeller. The third shop said they could send it away and get it the hub replaced, but it would cost $62 and shipping both ways. For that price, I could buy a new prop to begin with.

Also when I was on the phone with the Mercury guy, he suggested me adding some Mercury Quickleen. He said that the hub I have now, may have never in fact spun. Instead, the hub may heat up enough to slip. It could be due to it being worn out or excessive buildup in the exhaust. 

What do you guys think? What other preventative maintenance should I take on?


----------



## kbkid (Sep 30, 2009)

I pulled the trigger on a new prop this morning. Hopefully it will be here by the weekend.

What other preventive maintenance should I take?


----------

