Water pump impeller clearance

hi Murray

The water pump seal is spring loaded and I have never seen on with end play.  This suggests that the seal is failing or the pin in the drive gear (inside the engine) is worn.  The shaft is an interference fit to the drive gear for the impeller shaft.  You can see this in the heavy maintenance manual.  

Normally this is one of the 100% replacement parts on overhaul.  Clearance is checked using a "round" wire type feeler gauge.  These are commonplace for spark plugs also.  As you note a flat gauge will not really work for this check.

Cheers

Rotax Wizard wrote:

hi Murray

The water pump seal is spring loaded and I have never seen on with end play.  This suggests that the seal is failing or the pin in the drive gear (inside the engine) is worn.  The shaft is an interference fit to the drive gear for the impeller shaft.  You can see this in the heavy maintenance manual.  

Normally this is one of the 100% replacement parts on overhaul.  Clearance is checked using a "round" wire type feeler gauge.  These are commonplace for spark plugs also.  As you note a flat gauge will not really work for this check.

Cheers

Thanks RW,

I am not sure which pin you are referring to, the parts or heavy maintenance manuals don't show any pin in the drive gear. 

Given the seal is spring loaded, I thought if there is any clearance between the pump gear and the housing it sits in, it should be possible to move the shaft to the amount of this clearance? 

Which parts are you referring to with the 100% replacement on overhaul?

Hi Murray,

The pump shaft and parts are all one piece. The pin RW is refering to is probably the pump shaft.

Sorry for the confusion.  The pump shaft I have referred to as a pin is the same thing.  The shaft fits into the drive gear with a high interference fit and there is no referenced axle play to that shaft after install.  The fact that the water pump seal itself is spring loaded and interference fit to the shaft on the inside and loctite on the outer fit to the housing suggests that there will be no end play.  If you have end play you need it replaced.  

Cheers

Thanks for the responses.

The end play I am referring to has to be between the drive gear and housing. As can be seen in this reference from my Heavy maintenance iRMT class and is number 14 in the reference in the attached picture.

It shows a gap between the drive gear and housing but doesn't mention how much is acceptable. After all, if this gap was so close as to not have any end play the drive gear could start binding against the housing.

I am quite surprised nobody has noticed any play here and the design of the mechanical seal should allow for this with the spring loading. There is also no mention in the previous owner's logbook of any leaks so I think I will test it out before replacing it.

I checked my spare engine, and it has the same end play and hasn't leaked a drop. Will be interested to see if anyone else can find a water pump without any end play. I will try to measure the amount and report back.