1978 Mercury 9.8hp 110 thunderbolt

[curveball257]

hey guys i have a 9.8 mercury thunderbolt 110 model. It is a 1978 model. I was wandering if this type of motor had the hole that water shoots out of it from the water pump. it has an intake screen thing on the bottom of the engine right above the prop. it runs really welll but i cant see any water coming out of it that would be cooling the engine. I am afraid that if i run it i would burn up the engine please email me at curveball257@gmail.com if you could answer this question for me. Thanks

ramsey

 

[nbaffaro]

Re: 1978 Mercury 9.8hp 110 thunderbolt

Yes there is supposed to be a water stream. If you are looking at the back of the boat it would be on the right hand side. It will be towards the back of the motor but on the side. There are lots of things that can make the engine not shoot water. First I would take off the cover and you will see the hose that leads to the side where the water should be coming out. Make sure that is cleaned out and free flowing. If that does not fix the problem then you are going to need to take the lower unit off and put in a new impeller. It is rather easy. There are two bolts that hold on the lower unit. One is where the intake screen is it is a 1/2 nut and the other is on the leading edge right below the pivot. I believe it is a 9/16. Make sure that the engine is in nuetral when you are doing this and make sure and not twist the gear selection rod to make reinstallation easier. Once you have the lower unit off you can get to installing the new impeller. You will see the water pump housing at the bottom of the long 'drive' shaft. You do not need to take the whole pump out, just the top cover. Once you take the cover off you should the impeller. it will probably just be shards of plastic everywhere. Make sure and get all of the plastic out. There is a small key that holds the pump in place on the shaft. try and locate it and take it out. This was really the hardest part was getting hte old core of the impeller out. Once you have done so you can work the new impeller back in to the old spot. It isn't centered in the water pump housing. Some of the vanes are going to be compressed more than others. Once you have it in, put it all back together. Remember it only takes running the motor with out water for 5-6 seconds to destroy the water pump.
Did this on my friends 9.8 thunderbolt and it runs way better now.


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[Rover 310]

Re: 1978 Mercury 9.8hp 110 thunderbolt

Hi curveball257 & nbaffaro

This is a very useful thread for me, I have a great old Mercury 9.8HP (110) and I am wanting to replace the impeller, I have taken the front and rear nuts of the leg and eased it down 10mm or so but it wont come any further without force. (it has been together for 30 old years and been used in salt water)

I have taken the plugs out to turn the engine over and the gearbox is working fine in F,N & R. but I am worried that if I keep working the gear box off the leg I am going to damage the selector or something else.

So can you please confirm that I just go ahead and ease it out, making sure it is in Netrual, and then replace the impeller and put it all back together again.

Thank you very very much

Rover 310