sierra impeller problem or am i missing something pics includeds

[horiconducker]

Ive got a 1988 johnson 70hp. Ive always bought sierra water pump kits off here at boats and no problems with them. The first kit i bought in 2010 or 2011 the impeller had a brass hub. When i replace the old brass hub one in 2013, the new impeller had a plastic hub, didn't look to close at it and installed it. Fast forward to this year was still pumping great, only had 2 years on the water pump, then a few weeks ago it just quit pumping water all together. I ordered a new sierra kit from iboats and went to install it yesterday. When i pulled the old water pump apart impeller looked great but the key obviously had slipped, melted plastic, hub on impeller looked great. I installed the new one, but last night i started wondering how the key could slip. I started comparing pics of oem impellers to my impeller that was in when the key failed, things didn't seem right. I went and dug out my old sierra brass hub impeller and compared it to the the impeller that was in while the key failed and the new impeller i just received. The lip (that only allows the impeller to go on the shaft one way) is on different sides on the plastic hub impellers vs the brass sierra one(which looks identical to the oem impeller). Seems as the impeller will never really wedge on tight to the key. Im afraid this one will fail too. I am i completely missing something here??? Thanks ducker


These are pics of the the 2 different impellers. Both impellers are upside down in photo compared to how they sit while installed in the motor. See how the wedges go in different directions.

 

[schematic]

Sierra condones the reverse slot. Says its an improvement. There is a bulletin on it. I have used many with no issues.

 

[HighTrim]

The sharp edge of the cam is the leading edge during drive shaft rotation. So looks like the one on the left is correct in your pic? Which one is which>?

 

[horiconducker]

Yes my oem manual states to have the sharp edge of the key as the leading edge durning rotation. Yes i agree that the one on the left( brass one) is correct, the one on the right is the newer one that seems wrong. Does sierra recommend to install the key backwards then, or still with the sharp edge the leading edge, my kit does not specify which why to install the key?

 

[schematic]

the key will be installed backwards as well. It will only fit backwards. I have been through this all before. Even requested it in writing from Sierra.

 

[horiconducker]

My key, the bigger white one will fit either way

 

[schematic]

key goes in to fit the impellar profile

 

[HighTrim]

The OMC Engineers obviously designed it to have the sharp edge the leading edge. Im not smart enough to know why, but must have been a reason.

Sierra likely changed it for ease of manufacturing, or for cross fit between brands/models to increase profit margins. Just my guess.

I really don't like the Sierra impellers with the nylon/plastic hubs. Seen many where the drive pin tears a gouge through them, rendering them useless. I refuse to buy those ones anymore. Im not sure if Sierra still makes them with a plastic hub though.

 

[oldboat1]

H.T. has mentioned or discussed plastic hubs before (prone to failure). And there was another thread here recently on just such a failure, but don't think the OP followed up with the maker -- clearly not a brass hub.

A need to locate leading/trailing edges in impeller hubs is new to me. Based on the discussion, it looks to me like the impeller pictured on the left is right side up -- leading edge/sharp edge of the slot would contact the key turning in clockwise rotation. Based on the set of the vanes, it appears to me that the impeller was incorrectly used upside down(?)

hazzard a guess that plastic hubs pose a greater problem for higher horsepower, high torque motors. Getting the leading edge of the slot installed correctly, though, would presumably be an issue for all motors -- and brass hubs universally preferred if available.

interesting post.

 

[HighTrim]

I have seen plastic hub failure on motors with the "pin" style impeller key. It will just tear a groove through the hub. Not this style key. Regardless, I feel they are inferior, as I have seen a few failures. I stick with the brass hubs.

Oldboat, these style of impellers can only really go on one way. They will only slide over the key from one direction, as the other side of the brass is solid, the keyway only goes 95% of the way through the hub. So really, it is impossible to put them on wrong, and you wouldnt really need to think about it, they only go on one way, as long as you keep the solid side of the impeller hub UP. It is only when you notice that the Sierra and OEM impellers require you to put the key on the shaft opposite one another.

The "problem", if it is a problem, is that Sierra makes them so that the key is installed on the shaft opposite to what OMC recommends in its OEM manuals. I assume it still works like that, as Im sure thousands of them are in use as we speak, but curious as to why Sierra would manufacture them against what the manufacturer does.

 

[oldboat1]

Thanks, HighTrim. (Was thinking the slot on those impellers went all the way through.) In thinking about it now, I'm pretty sure I recall impellers for pin style keys that were similar (groove went about half way through the hub). Think that could have been a small Merc/Wizard, or Chrysler, but could have been for a Gale or other OMC -- thinking it was some time ago. The top of the groove was rounded to match the shape of the pin. (Not sure sometimes what recollections are real or imagined....) Good info.

 

[schematic]

The two impellers shown have brass hubs. The reason Sierra said that the cam was machined backwards was for "improved performance". As you all know, some cam locked impellers stick. With the hub and key put in reverse,.....they don't.
Non believers feel free to contact Sierra as I did. 877-663-8396
I change a dozen or so of these a year.....

 

[horiconducker]

thanks for all the replies, i was just trying to think how my cam had failed and and noticed the difference in the impellers. I will install the new one with the cam backwards from the instructions in the manual. thanks ducker

 

[oldboat1]

good catch. instructive. Thanks!

 

[horiconducker]

Just an update on this issue, I AM DONE WITH SIERRA WATER PUMP KITS!!!!!! Only brp kits for me from now on. The key on the water pump kit i installed last fall failed on me yesterday, only 3rd time in the water since i installed it. Stopped at the local dealer and picked up a brp kit on the way home. I think the key is a little bit larger on the brp kit. With the sierra kit, the key could be installed either way and the impeller would slide over just fine. For giggles I took the brp key and tried to install it with the old sierra impeller, impeller slid on easy one way, with the key reversed it started on the key but got tight, i didn't want to force it and ruin my new key. With the brp impeller and brp key, the impeller would only fit one way, not even close the other way. ducker