Yanmar 2GM20 water pump refurb - would this work

[Modulation]

The Johnson pump on my (then new) Yanmar engine lasted less than 400 hours before it refused to prime. I thought it was impeller wear so new impeller - no effect. On close examination, I found that the impeller vanes weren't reaching the pump body by a tiny dimension - but enough to cause pump failure.
These pumps cost serious money but I was lucky enough to be able to cannibalise one from my old engine so no sweat.
The defunct pump sits in my garage and, looking at it this morning, my thoughts turned to repair.
The problem is the vanes don't strike/meet the sides of the pump body - though they do strike it where the (integral)cam is. So a slightly oversize impeller would do the job. Trouble is there isn't on I know of. So what about slightly reducing the interior diameter of the impeller chamber - maybe lining it with a carefully cut piece of flexible acetate? Carefully stuck in place with a v thin film of epoxy?
Bonkers or worth a try?

 

[DinghyMan]

Do they need to strike all the way around? As long as they strike at at least one point it would pump water, not as efficiently as striking it more places though.

http://www.sailmagazine.com/diy/engines/impeller-etiquette/ looks like it only strikes at one point

I would have thought a repair using something like and epoxy would be better than acetate which is quite soft

 

[pete]

I eventually changed the (Johnson) pump on my 2GM20F at around 1100 hours after messing about with new impellers, a new face plate and better routing of the pipework and strainer. A new pump solved the problem but as you say it was expensive.

From memory my impeller was tight at the impeller tips and the webs were deformed when fitted, but the back/body of the pump had worn unevenly and was not making a good seal on the inside of the impeller.

If the impeller tips are shy of the pump body I would thing you had very little chance of it priming, are you sure that it is the right impeller ?

Not a good example but it shows the blades bending to fit in the pump housing, (not my engine by the way)
View attachment 51823

 

[RichardS]

The Johnson pump on my (then new) Yanmar engine lasted less than 400 hours before it refused to prime. I thought it was impeller wear so new impeller - no effect. On close examination, I found that the impeller vanes weren't reaching the pump body by a tiny dimension - but enough to cause pump failure.
These pumps cost serious money but I was lucky enough to be able to cannibalise one from my old engine so no sweat.
The defunct pump sits in my garage and, looking at it this morning, my thoughts turned to repair.
The problem is the vanes don't strike/meet the sides of the pump body - though they do strike it where the (integral)cam is. So a slightly oversize impeller would do the job. Trouble is there isn't on I know of. So what about slightly reducing the interior diameter of the impeller chamber - maybe lining it with a carefully cut piece of flexible acetate? Carefully stuck in place with a v thin film of epoxy?
Bonkers or worth a try?

If the vanes do not touch the sides anywhere other than on the cam then it must be the wrong impeller or the pump has worn very quickly perhaps in very silty water or something. You should be able to measure the internal diameter with a vernier gauge and compare the reading with the acceptable wear limit. Johnson will give you this or you might find it on the Internet if you look up the pump model number.

Richard

 

[Spyro]

Sounds like the wrong impeller. The diameter of the impeller is quite a bit bigger than the internal diameter of the pump. As the previous pic shows there is quite a bend to get it in

 

[ghostlymoron]

My pump is 40 years old but each blade of the impeller is bent to the shape of the pump chamber so I would assume yours is the wrong size. So must have been swapped at some time for the wrong one. Get the serial/model number and buy the right one from ASAP. I should change the seals at the same time and examine the shaft for wear.

 

[charles_reed]

As you refer to a Johnson pump and, in my experience the 2GM20 I had for 20 years, had a Jabsco pump, I'd diagnose a mismatch of pump and impeller.
The later 3YM's have a Johnson pump.
As posters have pointed out, the impeller vanes are deflected by the shoe and in constant contact with the pump body.

 

[bluerm166]

Modulation,If you don't have the Yanmar Workshop Manual to go with your expensive engine you should download it and will find it a revelation.The Owners manual ,certainly in older issues, is comparatively useless since the A4 format is carved up to show so many languages leaving room for only a few poorly referenced sketches.