Impeller on 1966 Merc 3.9

[mimsand]

Hi,
Recently purchased a 3.9 HP merc. The motor runs great but, the impeller has disintegrated. When attempting to replace the impeller, I don't know how the impeller is attached to the shaft. Generally, they simply slide up and off the drive shaft. This one is on there pretty solid and doesn't budge. How do you remove this bear>??

Michael

 

[rickdb1boat]

Re: Impeller on 1966 Merc 3.9

As you probably know, they are held to the shaft with a key. But if the impeller has not been off in some time, the brass bushing in the impeller can fuse to the shaft. The fastest and easiest way to remove it is to use a small sharp chisel and cut through the brass bushing that holds the impeller on. The brass is soft and will readily cut. Use care and chisel straight down parallel with the shaft so as not to damage the shaft...

 

[mimsand]

Re: Impeller on 1966 Merc 3.9

Hi Rick! Thanks for the help./
I got the old impeller off and the new one arrived today.
The new one is much too snug to go down on the shaft. I get it to within a couple inches and it stops. I'm afraid to drive it on with a hammer and shaft.

SO what gives? is it old and swollen er wut??

M

 

[AMD Rules]

Re: Impeller on 1966 Merc 3.9

Any chance your drive shaft has corrosion built up on it? If the new impeller gets thats close, it must be the correct size.

Does your drive shaft step up in the impeller area (speedi-sleeve repair previously installed?

Mine were so corroded over time, I needed to have them ceramic coated.Take a pic of that area if you can.


.

 

[Chinewalker]

Re: Impeller on 1966 Merc 3.9

Chances are you got the wrong impeller. There were TWO different shaft diameters used on the smaller Mercs. One used a .438 ID impeller, and the other used a .456 ID impeller.
It's also possible your motor's shaft is just too gunked up and needs to be cleaned up. Sandpaper or emory cloth half-wrapped around the shaft can help that along...
- Scott

 

[mimsand]

Re: Impeller on 1966 Merc 3.9

Thanks for that.
I sent the serial number along with my order. Surely I got the right one?

Anyways, here is a pic.

It's OK if I sand down the shaft to make it fit?


M

 

[Chinewalker]

Re: Impeller on 1966 Merc 3.9

You'd have to sand a lot to get it to fit and that steel is pretty hard. Why not just get the right impeller? Or, try opening up the hub of the impeller you have? Might be able to open it up enough with a round file to slide it down... The rlatively soft brass hub works much easier than the hard steel of the shaft.
- Scott

 

[mimsand]

Re: Impeller on 1966 Merc 3.9

I have a Dremel with a fine sanding disc. I will do that.

Thanks!

 

[mimsand]

Re: Impeller on 1966 Merc 3.9

Got it all re-assembled. Water flowed out of the hole on the side of the head for a few seconds when I started the motor the first time. Since then, steam and a small amount of water from the exhaust port on the back of the power head and from the small water hole on the side of the power head. Is this right? Is there a thermostat? Should I blow out the water system with air pressure? Is it operating normally with the steam coming from the exhaust port on the back of the power head?

How much water should I expect from the small hole on the side of the engine head? How much from the exhaust port in the bottom of the power head?

Thanks for all your help!!

My manual should be here soon and I can stop worrying you guys.

FYI, I am restoring a 40 year old Venture 17 from the hull shell up. This motor is the perfect retro addition. I have photos and am considering posting in your project section.

Michael