Changing the impeller on a '78 70hp Evinrude model 70873C. All spec tables say the impeller part # is 0382547. I ordered an online part from a reputable marina and they sent the correct part. Today I removed the LU to change the impeller and surprised to see that the keyway is much different. The impeller that was in there had what looks like a nylon half crescent moon and the impeller itself has a graduated cutout to accept this key. I've never seen one quite like this. I went to my local OMC parts dealer and all he had was the normal impeller with the straight keyway. The driveshaft is normal with a flat surface where the normal key would be. I recall one other impeller that had a normal keyway but the key itself was stainless that would fit the flat shaft and a normal keyway on the impeller. Any suggestions on either where I can get the correct impeller, or the key that would fit a correct part number?
Looks like the split was 1979, so maybe your '78 was a late production run with the "upgraded" shaft and impeller. Here's a '79 at marineengine.com which shows the wedge-type impeller being used (#58 on the diagram):
Probably right. I bought the other impeller on line and I've contacted them. Hope to return the one I have and maybe they have the other. Just have to pay shipping both ways.
Guess that's the price I pay for ordering the part before I removed the LU. Too soon old and too late schmardt.
A couple of other scenarios for you to consider. The gearcase could have been replaced on the motor & therefore picked up the newer design? You're right it can be confusing if you don't look before you order. The other thing is by looking at your shaft I think the motor originally had the interim impeller/key setup before they went to the wedge. The flat shaft design came about to stop shaft breakage. The first design had a round roller with a corresponding round slot cut in the impeller. The roller would move back & forth across the flat on the shaft. Therefore no wear to speak of. If you look at your shaft you can see this pattern. The later wedge type key & impeller will not leave this pattern & is cheaper still to produce. The latest design works well in salt water as well as fresh & is the accepted way of driving an impeller. Just thought you might like to know how it became this way?
I've changed several of those with the roller pins, I've also encountered a flat shaft with a SS key that fit the flat surface and a bump that fit the impeller. This is a first for me. The key on this one is white nylon. Funny thing is that when I first opened it up the white piece of plastic fell out and I thought something was sucked up. Wasn't 'till I looked at the setup I realized what I had. I ordered another impeller that comes with a new key from marineengine yesterday. I'll keep the other impeller 'cuz I have another motor that it will work on...â¦.I think