1974 Mercury 115hp Water Pump Issues

[jmark111]

Just a quick question about my project boat. Its getting very close to being water worthy in fact it has been in the water twice without leaving the boat launch. i replaced the impeller prior to going to the lake the first time. couldn't get the boat started. returned to the lake a few days later and got the motor started. during cranking the engine over i had a steady stream coming out of the tell tale. It was really high pressured and great! once i got the engine running about 10 minutes later, i was letting it idle and warm up. No water came out out of the tell tale. in the excitement of a running motor on my boat i through it in gear and started down the lake with my eye one the tell tale. I thought once i got moving that it would start pumping water, well... it didn't. Shut the motor down 100m from the boat launch and enjoyed a few hours floating on the lake. Returned to the boat launch under the power of my electric trolling motor. I dropped the lower unit today and inspected the impeller, sure enough it was melted. i have a new impeller kit ready to be installed once i get the housings all cleaned up again. My issue is i am very worried about putting in the impeller and this happening again. Question is WHY is it pumping such a good stream while cranking the engine and trying to start it and then basically stops pumping water as soon as the engine starts to idle? Water lines through engine cannot be blocked because it spits out such a strong stream while cranking the engine. Any help would be greatly appreciated!

 

[Chris1956]

Not sure what your issue is, as what you describe, should not be able to happen. Replace the waterpump cover, versus cleaning it up. inspect the waterpump base for melting and replace it if you find any. Replace the wearplate. impeller and the two gaskets. Make sure the impeller drive key is locking the inpeller to the driveshaft. make sure the thick rubber slinger is on top of the pump cover, against the cover.

 

[jmark111]

The impeller works great while im cranking the motor over and then as soon as the motor fires up it quits pumping water. That is my issue.

 

[jmark111]

What i think my issue is there is a rubber grommet or seal like thing that is the same diameter as tge driveshaft and i have no idea where it goes. Came off during the replacment of the original impeller

 

[jmark111]

replaced the impeller again and headed to the lake. and ended up floating around again! spits a great stream during initial cranking of the motor trying to get it started. (old motor that sat for a long time). once the motor fired up and was idling it was still spitting water! after a substantial warm up time. i through it into gear and nothing happened. slight grinding noise that would only be audible to a mechanic ear. girlfriend did not hear anything. tried gear shifter into reverse, clicked into gear like a charm, only issue was i was going forward. at this time the water outa the tell tale was still going. i figured hmmm what the hell so we cruised down the lake for about another 100m. Tell tale stopped pumping water and motor was turned off. any idea of what could be happening? i am going to replace the waterpump housing, gaskets and wear plate and potentially even buy the repair kit that changes out the lower section of water pump aswell. Do you think blowing compressed air into the tell tale would be a good idea? or would it be better to go through the water tube in the leg of the motor with compressed air?

 

[Chris1956]

Since she pumps water when cranking, but not when running, maybe the exhaust is screwing something up. I have a lot of experience with your motor, but cannot think of anything that would cause that.

Maybe the waterpump housing is not sealed allowing exhaust to get into pump? Just a guess.

Are there any cracks on the pump cover? Are you using the plastic tube on top of the pump cover to assure the water tube is inserted into the pump cover properly?

If she pumps water when cranking, the block is not clogged.

 

[jmark111]

That is a potential i guess having exhaust entering the waterpump. Due to no seal on the housing. Where is the exhaust come out on this motor? Through the prop and the two holes about halfway up the leg right beneath the lower cowl? Becuase i noticed it was spitting water outa the two holes. Could also be indication water is escaping outa the pump housing. Going to do the full waterpump repair and make sure thats not the issue. Very good chance it is.

Now any idea on why i have no reverse? When i shift into forward just wont engage. Nuetral works great. The strange part is when the motor is not running i shift into forward and the prop locks up counter clockwise and clicks rotating clockwise. Nuetral works great and free spins both dierections. When i shift into reverse with someone rotating the prop it engages gears and locks up in both dierections. I beleive that is what should be happenning but then everytime its in the water and i go to shift its all messed up! Lower unit i can shift by hand and vise grips (carefully) and to me i feel like im finding all three gears judging by the rotation of the prop.

 

[Chris1956]

The square ports under the powerhead are for idle exhaust relief. The do spit water sometimes. The exhaust megaphone is supposed to seal into the exhaust port in the gearcase, and send all exhaust out the prop. However, the gasket is often damaged and the exhaust leaks into the waterpump area.

On your gears. The shift slider on the side of the block should be about 1/2 way in it's travel, when the motor is in neutral. This assures the shifter has enough "reach" to get her in forward and reverse. It can easily get out of adjustment.

 

[jmark111]

well i found out why the water pump only spits water while cranking the engine over. i also figured out why my gears are backwards... Once the motor starts IT RUNS BACKWARDS!!! had no idea that was even possible! might start a new post now that i have narrowed down the issue.