1977 70HP Johnson

[Steele329]

Hi, I am new to boating and have a couple questions regarding my (new to me) boat. I bought it last year had it out a few times then the start solenoid went. No big deal replaced that all is well. The boat a 19ft 1978 galaxy bowrider. The engine a 1977 70HP Johnson. (M#70EL77S) (S#J47532) It runs very well considering the age, and I did to some tune up procedures of my own (Lower unit oil, fuel pump screen, basic clean up) I put it out on the river this past weekend for the first time this season and it still sounds great! What I did notice however is the exhaust relieve holes seemed to put out a lot more water last year than this year. After doing some research I learned that there does not need to be a steady stream of water necessarily, and I do not think I am running too hot, however I just want to be on the safe side. I want to change the thermostat and water pump but I have no experience with this. I work with my hands so it shouldn't be too tough (from what I read) but I cant find any info on exact procedures of dropping the lower unit or on how to change the stat. My questions - How do I change the stat and where is it? How do I drop the lower unit and do I need a new gasket on hand? Should I even be worried about all this? And finally, are there any other basic tune up procedures that I should take to keep this engine in tip top shape? Any and all help is greatly appreciated.

Thanks!!!
Tom

 

[boobie]

Re: 1977 70HP Johnson

Sounds like you can do something for yourself. I'd recommend getting an OMC Factory Service Manual as all procedures are explained in there.

 

[JimeeB]

Re: 1977 70HP Johnson

there are no special tools needed to change out a water pump. there are four bolts directly under the cavitation plate 9/16 i believe. There wil be one bolt just above the prop recessed in the housing. and another underneath your trim/anode tab. once all of those bolts are removed the ........ oops also on that motor you need to disconnect the shifter shaft from the linkage which is located behind the lower carb yes its a pain to get to, but with an extension and a wobble you shouldnt have any problems. after that the lower unit will be free to drop. you may need to rap on it or VERY CAREFULLY PRY it apart at first. Take note not to turn the shift shaft in either direction as the height of this rod is fairly critical. you will then see a plastic cover with four bolts holding it on. this is your water pump housing. before going any further make sure and have a rebuild kit or new pump on hand... once apart everything is pretty straight forward. remove housing by sliding up and off the drive shaft.. do not lose the key steel when removing old impeller.. there may be a rubber o ring on the top of the shaft inspect it and replace if needed. when reassembling take some vaseline or equivilent and put a thin coat on the inside wall of the pump housing. this will prevent the new impeller from burning up on initial start. also put some on the key steel and slide it into its slot. the vaseline will hold it in place while you install the impeller. to reinstall the impeller
slide the impeller down the shaft and seat it where it belongs. Slide the housing down the shaft and let it rest on the impeller.
you may need a friend for this part..... take a shop rag and wrap it around the top of the drive shaft. take channel locks and turn the drive shaft CLOCKWISE while a friend pushes the pump housing down onto the impeller. reassemble everything and your done.. The entire procedure start to finish should take no more than an hour...
hope this helps somewhat.
good luck.
one last thing I forgot.. when reinstalling the lower unit have a friend to help you, so one of you can look and make sure your water tube is engaging into the tube from the power head....

 

[mark1961]

Re: 1977 70HP Johnson

The thermostat is located under the cover with five bolts at the top of the cylinder head cover on the rear of the motor.....no special tools required.....just new parts (thermostat/relief valve) and a gasket.

 

[Steele329]

Re: 1977 70HP Johnson

Thanks! Im gonna give it a go ahead! Parts on order and Ill follow up with results asap! Any info on the thermostat?

 

[eavega]

Re: 1977 70HP Johnson

+1 on boobie's suggestion that you get yourself an OEM repair/maintenance manual. Pretty much every procedure you can do is listed there with fairly easy to follow directions.

The water pump impeller is fairly straightforward. I'll agree that the shift link is a bit tricky to get to. I'll usually loosen the carbs to get to it.
The thermostat is under the triangular plate at the back of the motor over the top cylinder. Three screws hold it in place, and mind a couple of springs that are part of a relief valve will go shooting out of the thing when you disassemble.

The Water pump impeller is definitely something you should check every year or two, especially if you don't know the history of the one in there. The Thermostat, well, if it ain't broke don't fix it. Check first to see if the motor is getting hot with either a non-contact thermometer or melt sticks. If it seems to be overheating, then start tearing into the cooling system.

Rgds

 

[Steele329]

Re: 1977 70HP Johnson

Eavega, thanks for the input. Just a quick question, I have read that if you do the water pump you should do the stat as they work hand in hand. Do you disagree? Is it best I leave this alone?

 

[mark1961]

Re: 1977 70HP Johnson

If the motor is fairly new to you and you dont know when it was last done.....a thermostat change would be my advice.....one less thing to go wrong and it isnt expensive.

 

[BonairII]

Re: 1977 70HP Johnson

Add a "telltale" to your motor. The pee stream lets you know that your impeller is pumping water....so there's no need to keep checking behind the motor for water flow.

There's a sticky in the Top secret file on the topic.

 

[eavega]

Re: 1977 70HP Johnson

Eavega, thanks for the input. Just a quick question, I have read that if you do the water pump you should do the stat as they work hand in hand. Do you disagree? Is it best I leave this alone?

Saying that the thermostat and the water pump work hand in hand is like saying the power pack and the stator go hand in hand. They are part of the same system, but can fail independently and either failure will cause the system to stop working.

If you are unsure of the state of the thermostat, test it. The procedure is fairly straightforward. Remove the thermostat from the motor. Pot of water on the stove with a thermometer. Suspend the thermostat in the water watch for it to open, and note the water temperature. Let the water temperature get to about 160 degrees, if the thermostat has not opened, its defective and needs to be replaced.
Assuming that the thermostat has opened, take the pot of water off of the stove, and add cold water to it to reduce the temperature and observe the thermostat closing again. If it has gotten below 130 or so and has not closed, then it is defective and should be replaced.

If you feel better with a new thermostat in the motor, then replace it. My take on it is that there are enough parts that need replacing on a motor due to normal wear and tear and component failure. Why spend money on a component that doesn't need to be replaced?

Rgds