Seahorse 18hp 1965 - impeller change

I just took the bottom half off an outboard for the very first time to prepare for a new impeller! I've read a lot about the process so things were where I expected, but I was surprised to find the cavity that the gearchange column had some black grease and a little water in there. Then I realised that there is a water inlet just above the prop and it looks like that might be where the cooling water enters the leg? So is that what should be in there or do I have a problem? When I've done the impeller should I be packing any grease in that area before I close it up?

Anyhoo, the screws holding down the impeller housing were tight on so I've left them soaking in WD40 for a while...

Re: Seahorse 18hp 1965 - impeller change

Help! I've removed the 3 impeller screws and tried to slide the housing up the driveshaft but it doesn't want to go - the driveshift is lifting out with the impeller housing? I don't want to mess anything up in the gearbox so have left it there. I've tried tapping the impeller housing to free it off the driveshaft but no luck.

Re: Seahorse 18hp 1965 - impeller change

Edit - persuaded the housing to come off! The impeller itself looks OK - the rubber vanes are flexible and there doesn't appear to be any bad wear and tear. Am I correct in thinking that the impeller housing is not a "perfect circle" - the impeller looks not be sitting perfectly centrally ie the vanes are more curled on one side than the other. I assume this is to do with the efficient functioning of the pump? I expect the advice would be to change the impeller anyway, but given I have to buy everything from the US I'd rather avoid the expense if possible.

Re: Seahorse 18hp 1965 - impeller change

The housing is "elliptical" which is what makes the pump function; if you don't know when the impeller was last changed you should replace it since you are already in there .Some auto supply stores in the US also have a marine parts section although they don't advertise them much; maybe you have some over there. Good luck.

Re: Seahorse 18hp 1965 - impeller change

It is fine to pull the drive shaft up and out, you wont hurt anything. Just slilde it back down and in when you are reinstalling.

Be sure to coat the impeller housing screw threads with gasket sealing compound before installing the impeller housing. I would definately change the impeller while you have it apart.

Also be sure to change the o ring at the top of the drive shaft, and greas the splines.

Put a little grease in the grommet of the impeller housing, where the copper water line slides in to help with reinstallation. If that grommet is damaged, replace it as well.

Now regarding the grease, could you post a pic of the area you are referring to? There should be no grease packed into anywhere in the gearcase cavities. In fact there are little pin holes for drainage, ensure that they are not clogged so that the gearcase cavities can drain when the motor is pulled from the water.

Re: Seahorse 18hp 1965 - impeller change



Hope these pics show up OK. My reason for looking at the impeller was because I got the engine running, had a good water stream coming out of the exhauset, but after 5 minutes it stopped. But now I've seen the impeller it doesn't look bad, so what could have stopped the water spitting out of the exhaust. I will try to find the inlet and make sure it's not clogged, but it was working to begin with so I don't suspect that.

Re: Seahorse 18hp 1965 - impeller change

That cavity down by the shift rod bushing should be clean. If water is pooling in there, the drain is clogged and will need to be cleaned out. If water sits in that cavity over winter the casing will crack. If you look on the side of the gearcase you will see a tiny hole where water will drain from that cavity.

Your impeller orientation is correct.

Regarding the loss of water flow. First ensure the intake area is free of debris. Next ensure the pin for the impeller did not break or get lost. Also ensure that the copper water line does not get pinched when going into the rubber grommet on top of the impeller housing. While the gearcase is down, shoot compressed air up the water line to ensure there are no blockages in the cooling circuit and the air exits at the exhaust relief.

Get a new impeller.

I have seen where the Sierra impellers fail like this as well. Their hubs spin, or the center hub gets destroyed by the drive pin. Stick with OEM impellers if you want to keep your motor. Sierra is ok for some things, impellers are not one of them.

Re: Seahorse 18hp 1965 - impeller change

Great thanks Chris -will do.

Steve