help please with direction and mounting of Yanmar water pump

Northeaster · Jun 21, 2016

Hi Folks - I am building a 25ft aluminum fishing/pleasure boat with an inboard Cummins 4bt 150hp diesel. I have to rig up a 2nd water pump to circulate the seawater through the transmission oil cooler, engine heat exchanger and then out the wet exhaust. I regret cheaping out and not buying an OEM gear driven Cummins seawater pump when one was available at a reasonable price...Instead I bought a Yanmar 18-1930 water pump and added a pulley, belt from the Cummins crank/ accessory pulley, fabricated a backplate from aluminum and bracket to mount it.

Well, I tried it today and it didn't work..... I am thinking I have one or both of the below issues and maybe more... help please!!

1. Which direction should it spin, when viewed in pics below? I first thought it would spin counter-clockwise (so impeller pulled water from narrow channel to wider channel, perhaps creating some vacuum....now wondering if it should spin clockwise so water is pushed from wider channel towards narrow to create pressure.
I tried spinning it in both direction by hand, with backing plate on with gasket maker, and both hoses primed/ filled with water - with no results at all...and no resistance I could feel- which leads me to #2...

2. When mounted on a Yanmar tractor or engine, does it mount on a seal of some sort or raised area in middle, so it reduces the gap between the center and the backing plate/ mounting area? I didn't look close enough before but looks like there is perhaps a 1/16" gap so the impeller is recessed and does not touch the backing plate. I now assume that any gap of significance would mean the pump cannot create any vacuum/ push/pull of water, etc..

Any help or suggestions would be appreciated!

bigdeano · Jun 21, 2016

Looks like it's just a simple centrifugal pump. It should turn clockwise and will pump from the center inlet to the outer connection, judging by the shape of the housing. Turning by hand is too slow, has to turn fast. It will work bolted to a flat surface since the water inlet is at the other end where the clearance is probably less.

Isn't it going to rust badly with a cast iron impeller? It's made to fun in antifreeze. Seems like you'd want a bronze pump.

Northeaster · Jun 21, 2016

good point about the rust - I didn't really know what it was made of when I bought it on-line. if I can get through one summer, \i would be happy at this point, and do something better next winter.

Well, |I have it spinning clockwise (when viewed from the front / pulley end) but there was no suction or pumping even at 2000 rpm or more, with the lines primed with water... I will have to measure the distance from the center of the impeller to my backing plate, and if there is any gap like 1/16" or more, I may tack in a shim to reduce the area between the impeller and backplate. I know on the rubber impeller sea water pumps if the backplate is scored at all (increasing the gap) it greatly reduces the efficiency. On some you can turn over the backplate to have a fresh / flat surface for the impeller after one side is too badly worn.

I may just rig up a cheap electric pump for the summer as well..... thanks for the reply and help!

bigdeano · Jun 21, 2016

Strange that it wouldn't pump. There must have been some air in the pump. The discharge connection would have to be at the top to let all the air out I would think.

Clearance at the open end of the pump shouldn't affect anything because the center of the impeller is closed at that end. On some engines there isn't any discharge connection, the water just goes right into the engine from the impeller, so it's just open in the back.

Northeaster · Jun 21, 2016

I really appreciate you taking the time to reply and help!

I assumed there was no air, as I poured water in one hose and it ran out the other, so thought the pump would be then full or partially full of water. I even kept the ends of the two hoses (about 5ft each) higher than the pump.

It did seem like there was zero resistance. Maybe the water flowed by the impeller but air was still trapped there. But what else could I try?

I see your point about the engines with open mounting, and therefore much more of a gap than I have. But, I fail to see how it would actually create any pumping force, if water can just go in any direction and not follow a certain path around the impeller, like if there was no gap behind it...

I am stumped...

bigdeano · Jun 21, 2016

The water flows from the center of the impeller to the outer edge. As long as there's not a leakage path back to the center the pressure isn't lost. Since the center of the impeller is closed off on the rear end that we're looking at, the water has to go out the outlet fitting.

Northeaster · Jun 21, 2016

The one shown in the picture is actually a 2nd pump - they were cheap so got two at the time (one for another purpose) The one I tried on the boat is identical but I removed the collar and pressed on a sheave / pulley - got lazy and used a big vise to press it on rather than hone out the hole in sheave for an easier fit... I put a block of wood behind the impeller while pressing to prevent damage - I wonder if I may have pressed impeller a bit further onto the shaft, perhaps blocking entrance holes, etc and preventing it from working the way it should..... if that's a possibility, I could try the spare one....

bigdeano · Jun 21, 2016

If you moved the impeller very much it wouldn't turn. Try running water into the inlet and see if it goes thru the impeller just to make sure you have free flow.

I presume the shaft is horizontal when you're running it. Do you have the outlet at the top so the air can get out?

Leejohn · Jun 21, 2016

It well not work. That is a circulating pump and well not put out the pressure and volume you need. Sea water pumps are rubber impeller pumps that put out around 40 psi deadhead pressure and a lot of volume. The hoses should be no less then 3/4" feeding the exhaust and engine block. The thermostate housing well need to be for a set up like this. One that makes sea water pump that I can think of right now is Johnson Pumps. I might have a drawing of how water flows in a marine engine, not for sure but well check.

Northeaster · Jun 22, 2016

Leejohn - thanks for the info / confirmation that the pump will not work. I am familiar with rubber impeller seawater pumps - have one on my 38 year old sailboat with a little Yanmar 2GM diesel. I do have correct setup on the new boat / Cummins 4BTM (marine) including 1" hoses to gear cooler then engine heat exchanger (was on a 8 cyl chev powered boat so should be large enough) and have all cooling lines set up correctly I believe.

Only issue is me cheaping out an not buying proper gear driven Cummins pump (just checked they are about $500-600 now plus tax, exchange and shipping...), or at least a good Johnson or other seawater pump driven from the crank / harmonic balancer as set up on many inboard boats.

I only paid $2000 for the used Cummins 150hp engine (has 4000 hours on it) so I have trouble paying $700 for a seawater pump now....but that's my issue - boat dollars and wife's patience running thin at the moment after 3 winters of building and spending big $$$$ on lots of large aluminum sheets.

If I can just get boat in water, and it performs well, I won't mind doing more work and spending more $$ next winter, but as it stands I don't want to spend much more until we see it work in water...just for some positive affirmation...incentive
to continue..

Likely rig up a $30 electric pump to try in water for now. have to buy axles and build trailer quick to test boat this summer, before I go insane...

Thanks for all help - if anyone knows best type cheap electric pump to try for now, let me know - Note- know a mechanical pump is much better as it will run without electricity as will the engine, if alt or battery filed while off shore...and it was still running... this would be temporary..