Powerhead swap?

[rustyscrew]

I am wondering if anyone knows whether the powerhead on a 78 merc 1400 (inline 6) is the same as the powerhead on 79 115. It looks like the displacement and bore are the same. The stroke is slightly different. Does this matter?

I was the post for the "thumping sound of 78 merc 1400" and it looks like the crankshaft has sheared. So I am looking to replace the powerhead and I found a 79 merc 115.

 

[Chris1956]

Re: Powerhead swap?

Rusty, As long as it is a inline six, it should bolt up. The blocks were the same, except for the port timing, and maybe pistons.

The crank on your '78 did shear? I had never thought that possible. What caused it?

 

[rustyscrew]

Re: Powerhead swap?

It is still premature to say that it sheared for sure. My mechanic suggested it and I have suspected it based on the sound and the fact that there is side to side play in the flywheel. I can rock the flywheel a little bit. Every other outboard I have compared it to doesn't have any play at all.
It is possible that it is something else though...

Instead of trying to fix the one I have, I thought I might be able to replace it with another.

Thanks for your comments.

 

[Chris1956]

Re: Powerhead swap?

Rusty, There is a large bearing on the crank, under the flywheel. Perhaps that went bad. If so, you should be able to replace it without disassembiling the motor. You would need to unbolt the outer flywheel, remove the stator and pull the inner flywheel. Now remove the four 5/16 bolts holding on the upper bearing cover. You will need to loosen the top bolts on the crankcase, so you can slip the bearing cover off. The bearing will either come off in the cover, or need to be pulled from the crank. Watch for loose pieces. A replacement bearing is likely less than $50. Save the shim under the bearing cover, and reuse it.

 

[rustyscrew]

Re: Powerhead swap?

thanks chris, I will try that. I was going to pull the flywheel off last friday, but I need to track down a puller. I am even more excited to pull it off now though...d

You answered a question in the johnson/evinrude forum for me. You get around!

Turns out, when I remeasured the shaft length of the 1988 evinrude 120 hp, it actually fits the boat perfectly...whew!

That is the potential replacement engine for the old merc 1400. No pre-mix, power trim, cleaner....its hard to pass up even though I love that merc 1400!

Thanks...keep ya all posted.

 

[Chris1956]

Re: Powerhead swap?

Rusty, Don't sweat the pulling of the inner flywheel. They have a "w" shaped groove machined into the crank and flywheel instead of a key. A lot easier to remove. Pry it up with a tire iron and give it a good rap on the crank end (nut flush with threads right?), and it might pop off. Give it a blast of penetrating oil first.

 

[rustyscrew]

Re: Powerhead swap?

I should run and look at my book, but when are you talking about removing the flywheel that is at the top? The one you would wrap a cord around?

Just wondering because I would love to not buy the puller right now, but it seems that everything cautions against using anything but the real puller.

I have access to external pullers, but I have heard that they can damage the flywheel.

thoughts on this?

thanks

 

[Chris1956]

Re: Powerhead swap?

Rusty, The flywheel is in two parts. A stamped outer flywheel with the magnets, and the inner flywheel. The inner flywheel is solid steel (likely stainless) maybe 8" in diameter. The outer flywheel is held on by 8 5/16" fine thread bolts. Now the outer flywheel is a bit flimsy, and could be damaged by using the wrong puller. The inner flywheel is solid steel, and you should be able to pull it with just about any puller. I used a hermonic balancer puller the last time, but I used a tire iron prior to that, when I was too lazy to hunt up the correct bolts for the puller.

One note on the oil injection of your '79 115, I have no direct knowledge, but have heard that the early injection systems were not robust, and could fail. You might like to solicit some advise on this feature.

 

[rustyscrew]

Re: Powerhead swap?

Chris, thanks again. The oil injection system is for the 1988 evinrude 120 that I bought. I looked into adding oil injection onto the merc 1400 that I have been running when I first bought it, but I came to the same conclusion that you did. So I have just been premixing 50:1 ever since.

The way my boat is designed, it tends to vortex the exhaust back into the boat so after 8 hours of trolling for salmon, I start having dreams of oil injection!