1976 40hp Johnson cooling problems

[KarstRanger]

I am trying to fix cooling problems on my old 1976 Johnson 40hp outboard. It has sat up for about 8 months, but seemed to be cooling ok when I last used it. I just test ran it in a garbage can, and there was no water shooting out of the foot where it should be and it was well on its way to overheating when I shut 'er down.

If you read the Johnson/Evenrude manuals on these older motors, they expect you to replace the impeller about each new season, so hopefully some of youall have done this before in your own backyard.

After checking for mud daubers and etc with a coat hanger in the exhaust and water passages and finding nothing, I decided it needed to be pulled apart.

The problem was pretty obvious if you take a look at the brass center of the impeller -- the impeller was not spinning:





From what I could tell- the little key (impeller drive pin) in the driveshaft had come loose and slid down out of position where it did not stick out as far and was not making contact with the impeller. Also, apparently it or something had damaged the inner brass fitting on the impeller.




The key will not fit back tightly into the driveshaft even with some scoring by me, so I am going to order a new one -- unless someone can tell me how to get it to stick in that slot. The slot in the driveshaft appears undamaged.

However, I am wondering if the slot in a new impeller would keep it tight.

Another question is this: There were no gaskets on each side of the impeller housing plate when I took this apart (the mechanic who replaced the impeller the last couple of times has moved away, so I can't ask him)- Anyway, he had carefully scraped away the old gaskets and just put it back together metal to metal. No Form-a-gasket, no nothing.

Well, of course I am blessed with the one Johnson outboard that they only made two of back in 1976, ha ha, and I have to go to a Johnson dealer, no aftermarket cheaper parts for me this time

The impeller only - no gaskets costs about $35.

The water pump repair which is the only way to get the gaskets costs about $75, and I don't need all the other stuff in it.

Any opinions on whether I should try to save the $40 and don't use gaskets? The gaskets go on each side of the shiny plate (impleller housing plate)below the impeller:



Thanks !

[FUTCHCAIRO]

HEY K.R. JUST PUT A BEAD OF BLUE SILICON AROUND THE FITTINGS, BE SURE NOT TO FILL ANY WATER PASSAGE, BOLT IT BACK TOGETHER AND LET HER SIT FOR A COUPLE OF HOURS BEFORE SUBMERGING THE FOOT, SHOULD BE FINE.
PA THE OLD MAN OF THE SEA

[KarstRanger]

OK - no gaskets it is - I just wanted someone else to tell me it was OK because I wasn't sure...

But what do you think of the heavy scoring inside the impeller? That's the real problem here. I am supposing that maybe the original key in that old of a motor could have gotten worn down -- so I will try replacing that key.

[Nathan]

Sierra makes all of the maintenance parts for the old OMC motors now. Doesn't matter if you buy it from a Evinrude/Johnson dealer for big bucks or a discount place online, it's the same parts in different packaging. You should be able to buy a water pump rebuild kit without the housing. The housing adds $20 or so, at least, to the cost. As long as the housing isn't cracked it should be fine. The water pump rebuild kit comes with all of the gaskets and rubber seals that should be replaced when replacing the impeller. Good water flow from the impeller doesn't do any good if it never makes it to the cooling ports in the block. It looks to me like that impeller has been in there for quite a while. Definitely time to replace it.

Nathan

[KarstRanger]

Sierra makes all of the maintenance parts for the old OMC motors now. Doesn't matter if you buy it from a Evinrude/Johnson dealer for big bucks or a discount place online, it's the same parts in different packaging. You should be able to buy a water pump rebuild kit without the housing. The housing adds $20 or so, at least, to the cost. As long as the housing isn't cracked it should be fine. The water pump rebuild kit comes with all of the gaskets and rubber seals that should be replaced when replacing the impeller. Good water flow from the impeller doesn't do any good if it never makes it to the cooling ports in the block. It looks to me like that impeller has been in there for quite a while. Definitely time to replace it.

Nathan

Thanks for the info and about Sierra, Nathan --- You can bet I am replacing the impeller -- "it is past ruint" (as they say around here...).

I checked Ebay Motors and some other web sources for the part# I need and couldn't improve much on the price from this dealer up in New York. I was only sort of kidding about that they only made a few of this particular model 40hp -- there seems to be alot of parts availability for other models, but for the 1976, it really is limited. You either can get the impeller by itself or the water pump repair kit which includes the housing you mentioned (that I don't need, but oh well).

In any case, my main worry is that a new driveshaft key and a new impeller may not fix the looseness problem that allowed the impeller center brass to get all torn up like in the pictures. I suppose the only way to find out is to put the new parts in when they arrive and see if it fixes it up right (and not drive the boat too far from the dock that first run!).

[FUTCHCAIRO]

WHEN YA PUT THE KEY IN THE SLOT OF THE SHAFT, DIP IT IN SOME EPOXY RESIN AND THAT WILL TAKE ANY LOOSENESS OUT. LET IT DRY FOR A FEW MINUTES BEFORE CRANKING OR TURNING THE ENGINE OVER.
PA THE OLD MAN OF THE SEA