SS replacement head not working on old March pump

[corax]

I got the Chugger stainless steel replacement head to replace the polysulphone head on an old March 815-PL pump:

https://www.morebeer.com/products/chugger-pump-replacement-stainless-wetend-assembly.html
The above site explicitly mentions the 815-PL as being compatible, but the pump does not run with the SS head. The motor hums, and the fan in back gives a little jerk, but it won't pump. If I put the polysulphone head back on, it runs fine.

Nothing seems to be interfering with the impeller in the SS head; it spins freely when I open up the housing.

I'll definitely call MoreBeer customer service when they're open tomorrow, but thought I'd check here to see if anyone had ideas or similar experiences.

One thing I noticed when I was putting it together was that the SS head virtually jumped into place on the pump-- ie, it was fully magnetized. Could the magnetized housing be interfering with the action of the magnetic impeller?

 

[brewbama]

Does the head touch the magnet on the motor side? If the fan in the back of the motor is not turning the motor is not turning. With the SS head installed, try unplugging it and turning the fan with your hand. If you can’t Turn it, it would indicate to me than the magnet between the motor and SS housing is making contact. You’ll need to set a slight gap.

 

[day_trippr]

I'm betting it's an alignment problem on the drive magnet - not an impeller issue at all.
I remember our friend Walter from March saying it's critical to get that alignment right...

Cheers!

 

[corax]

Thank you brewbama and day_tripper, I think the problem is solved.

It wasn't an alignment issue (pretty much identical alignment between the plastic and SS heads, and the plastic head worked), but the fan could not be manually turned with the SS head in place.

The main difference in the guts of the two is that the SS head includes a couple of teflon (?) rings to keep the impeller from directly contacting the metal housing. The larger of the two rings (inside the outer cup) was slightly bent inwards -- I guess putting just enough pressure on the impeller to keep it from spinning. I flattened it out as best I could, and it now works!

 

[brewbama]

It should work better as it wears in a bit. Cheers!