1979 7.5HP ES, Water Pump Refurb

[troyt]

The pee stream on my OB has degraded to practically nothing over the last few months. I found a refurb kit for about $26, and the lower unit looks like a breeze to R&R. My Clymer manual talks about pressing some seals, and there is a lengthy dissertation on shimming. Are these as difficult as the manual makes them out to be? Also, I'm seeing two different diameter impellers for the same year. Does anyone know approximately what serial number range that they changed over?
Thanks,
T

 

[Laddies]

Re: 1979 7.5HP ES, Water Pump Refurb

There is no shimming needed to change a w/pump or seals unless you deside to change the driveshaft seals while it's apart

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

Thanks for the info Laddies.
I went to pull the lower gear case and was very surprised to see that the nut below the cavitation plate holding the back half together was not there! I doubt a nut with a nylon insert would work its way all the way off, so I think it was left off during a service by the previous owner. Can I just go buy a stainless nut with nylon insert, or is there something special about the stock nut?
I tore down the water pump to the base and it was a breeze. I measured the impeller several places with a micrometer. All were .45+ so I ordered the rebuild kit with the .456 ID impeller from oldmercs.com. I used compressed air to check the passages for blockage. Top to bottom and bottom to top were clear. I did notice if I blocked the bottom end of the water tube coming out of the shaft housing, the air blew out inside the top of the housing. Is there a pressure release or bypass up there?
I can't wait to get the parts and get her back together.
T

 

[Laddies]

Re: 1979 7.5HP ES, Water Pump Refurb

Any s/steel fiberloc nut will work for the missing nut, there are no reliefs or anything like that in the engine, if the impeller has broken fins try to find the pieces and seal the intake pipe grommits before assembly

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

So I got the parts and put everything back together. It went very smooth. I then filled the ice chest tub that I always use to flush the engine with water. She starts right up, but no water stream. I get a few sprayed water droplets occasionally and mostly steam, with maybe some exhaust. I don't run it for more than a minute or so for fear of overheating. I was figuring I would take the lower unit back off this weekend and try water starting from the water tube up to see if there are leaks (easier to find with water than compressed air) until I read another thread here about a 9.8HP with a similar issue. Keep in mind I have used this same tub to flush this engine with a worn impeller. Is it possible that the new impeller is pulling so much more suction that it is getting too much exhaust to prime? I think I will try tilting the engine like the other guy did to divert the exhaust from the prop away from the pickup under the cav (vent) plate. Otherwise, where are the grommets on the water tube, and do I have to remove the drive shaft housing to get to them?
Thanks,
Troy

 

[Laddies]

Re: 1979 7.5HP ES, Water Pump Refurb

The grommets are on the short tube between the pump housing and the cavitation plate usually a sealer like sealer 1000 works fine on them.

 

[MercruiserMan]

Re: 1979 7.5HP ES, Water Pump Refurb

Could be your water tube never aligned up properly with the tube in the upper case area. Had this happen to my 7.5hp

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

I had a chance to try some more troubleshooting today. I ran the engine in the tub with the tilt out a little. Still no water stream, and the gas coming out is mostly exhaust. Pulled the foot and tried to pump water turning the drive shaft. I didn't get any water out until I submerged the intake tube between the intake and the pump body, so Laddies was right. I know I need to seal those grommets. Here is the more disturbing results. If I force water from the outlet tube leading to the pee stream at the top of the engine down, most of the water is coming out on the inside casing of the drive shaft cover. Very little is coming out of the water tube. If there a sealing point at the top of the tube, and do I have to remove the drive shaft cover to get to it?
Thanks for all the help so far. I don't want to let this one beat me.
Troy

 

[Laddies]

Re: 1979 7.5HP ES, Water Pump Refurb

Troy, 90 to 95% of the coolig water comes down the driveshaft housing so your probably alright

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

After sealing the intake tube grommets, I can pump water by hand cranking the shaft with just the intake in the water
I also sealed the water tube coming out of the top of the pump body to the pump body. Do I need to put sealant on the water tube going up the shaft housing to seal it to the pump outlet tube? This connection seems very loose on both the old pump outlet tube and the replacement.
T

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

I went ahead a put a bead of sealer around the water tube, bolted the lower unit back on, and let it set up overnight.
Set everything up the next morning, started her up. I get a nice stream of water, interrupted only by the exhaust coming out of the prop. Let it run till it got nice and warm. Everything runs great!!
Thanks to all here for the helpful advice. I learned a lot and won't think twice about doing this or other outboard repairs in the future.
Virtual bar is open, drinks are on me!!!
Troy

 

[Lakester]

Re: 1979 7.5HP ES, Water Pump Refurb

hello,

good to see u solved ur prob. but i am a bit confused.

could you please state in one sentence what ur solution was?

i am not sure if u needed a seal, a water tube was out of place or?

thanks...

regards,
lakester

 

[troyt]

Re: 1979 7.5HP ES, Water Pump Refurb

Lakester,
My problem was I did not seal around the grommets securing the water intake tube located between the pickup and the pump body. This was Laddies suggestion and I proved it by hand turning the crank shaft with the lower unit off. With just the pickup submerged, I would not get water through the pump. With the pick up tube submerged, water would pump (keep in mind that you have to crank rather quickly to defeat gravity). After I added sealant and let it dry, I could pump water with just the pickup under water. I applied sealant to the pump outlet tube/shaft housing water tube connection just to be safe.
Troy