# Impeller clearance issues



## BigTerp (Oct 8, 2013)

My impeller clearance varies from less than .020 to over .027 in different spots along the liner. If I rotate the flywheel the clearances stay the same along the liner. Almost as if the liner is worn or warped in those spots. If the shaft was bent the clearances would follow the impeller as it turns, same should go if the impeller blades were worn. Make sense? I inspected the liner when we rebuilt the motor (1994 Johnson 50/35) and all looked good. I don't think I did, but maybe I missed something. Any other ideas of why the clearance varies so much along the liner?


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## Ranchero50 (Oct 8, 2013)

Bad luck and other junk going through the pump. You should have a series of stainless washers above and below the impeller. Shift them to get the clearance you are looking for. .007" isn't a huge difference tight to loose.

Just make sure you run it and recheck the clearances. Last one I did ended up a bit tight and wouldn't start after running for a while at the ramp. #-o


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## BigTerp (Oct 8, 2013)

Thanks Jamie. I considered shimming the impeller down a bit, but am afraid that the spots where the clearance is already tight (under .020) it might cause issues? My manual says for clearance to be no less than .020 and no more than .027. It's already under .020 in spots. Think I should still try and shim it down a bit?


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## Ranchero50 (Oct 8, 2013)

I'd leave it alone. Your impeller is going to move around, your shaft will flex some as it eats stuff or cavitates. As I found out once it hits the liner, it'll gall and self destruct until the impeller gets locked up.


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## Scottinva (Oct 8, 2013)

I think the recommended clearance is .031". I have had an issue where I had less than that and the motor would not start. Once I got the right clearance, it started fine. I know of others that have had the same issues. Mine would start fine in the summer, but in the winter when it was 32F outside, it wouldn't.

Scott


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## PSG-1 (Oct 8, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=331608#p331608 said:


> BigTerp » Today, 12:48[/url]"]My impeller clearance varies from less than .020 to over .027 in different spots along the liner. If I rotate the flywheel the clearances stay the same along the liner. Almost as if the liner is worn or warped in those spots. If the shaft was bent the clearances would follow the impeller as it turns, same should go if the impeller blades were worn. Make sense? I inspected the liner when we rebuilt the motor (1994 Johnson 50/35) and all looked good. I don't think I did, but maybe I missed something. Any other ideas of why the clearance varies so much along the liner?



Not sure about outboard jets, but with PWC pumps, especially those used in saltwater, corrosion builds up between the aluminum housing and the stainless liner of the wear ring assembly. This corrosion will actually swell the liner, causing a high spot where the impeller will hit as it's rotating.


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## BigTerp (Oct 9, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=331631#p331631 said:


> Scottinva » Yesterday, 4:41 pm[/url]"]I think the recommended clearance is .031". I have had an issue where I had less than that and the motor would not start. Once I got the right clearance, it started fine. I know of others that have had the same issues. Mine would start fine in the summer, but in the winter when it was 32F outside, it wouldn't.
> 
> Scott



Weird!! I just checked outboard jets website, and they reccommend a clearance of .032". My manual reccommends a clearance from .020"-.030". I guess the general idea is to get it as tight as possible without the impeller whacking the liner? I still need to pull the foot and check the liner to see if it's been getting dinged up from the impeller. But as of right now, having a clearance in spots below .020" I'm thinking I shouldn't attempt to shim the impeller down any.


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## BigTerp (Oct 9, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=331616#p331616 said:


> Ranchero50 » Yesterday, 2:27 pm[/url]"]I'd leave it alone. Your impeller is going to move around, your shaft will flex some as it eats stuff or cavitates. As I found out once it hits the liner, it'll gall and self destruct until the impeller gets locked up.



Thanks. I guess it should be pretty noticeable if the impeller is hitting the liner?


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## BigTerp (Oct 9, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=331634#p331634 said:


> PSG-1 » Yesterday, 6:18 pm[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=331608#p331608 said:
> ...



Thanks. That makes sense. Outboard jets also says "There is some off center between impeller and liner due to manufacturing tolerances so check at the closest point." So I guess the variance in clearances I'm seeing is nothing out of the ordinary.


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## Canoeman (Oct 9, 2013)

They all have some variance due to casting etc..

I try to get it as tight as i can, i dont use feeler gauges etc.. just get it so it doesnt hit the impeller.. 

And yes.. ive got it to close so when your trying to start it on the water it hits the liner = no start 

Get it close and run it man


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