At Cottage - Evinrude 70773S stopped working

[acolic]

Hi

I was out tubing with the kids and my boat jumped over another boat’s wake. The motor sounded like it was sucking something up and shut off.

It restarted and we continued when after another 5 min it shut off.

I had to use my trolling motor to get back.

I can’t get it to restart.

Here’s what I have checked.

1. Electricity is going to each cylinder.
2. I have changed the spark plugs.
3. Without any spark plugs in the motor, it rotates fine. Very fast.
4. With the top two spark plugs in the motor, it rotates very fast.
5. With the bottom spark plug in, it rotates very slowly.

Any suggestions?

Thanks

Alex


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[Zum]

Newer motor?
Can't see going over a wake hurting much, unless may e you did suck something up and your motor has an alarm or protection against overheating? When you started it after the first shut off was it pumping water?
It will "spin" easy without plugs, with them all in there compression, "spins" harder....if that's what your talking about.
Fuel, lots of it,motor getting it?
Maybe a short, on/ off switch possibly...wire or switch moved when you "bumped" abit?
Give the type, year motor, tiller etc...Might helps us abit.

 

[acolic]

It’s a 1977 2 stroke Evinrude 70773S.

Alex


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[DaleH]

Dumb question ... but did you check to see if the gasline is still connected? Maybe it wasn't on good enough to survive the hard landing? Always check the easy stuff first, like also confirm that the kill lanyard is correctly affixed.

 

[acolic]

Hi

Yup gasoline is attached properly and so is the kill switch.

I also checked the fuel filter and it’s fine.

Why would only one cylinder be hard to turn but not the others?


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[GYPSY400]

Sounds like it over revved by jumping the wake and blew up.. check the compression.

 

[acolic]

Ok I’ll check the compression.

But what blew up?

Are we talking about a new cylinder? Rings?


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[GYPSY400]

Perhaps.. its a 40+ year old motor, anything can happen. Check compression and go from there.

 

[maintenanceguy]

I'm with DaleH. I think something just got knocked loose and if you find that thing you'll be fine.

But...

"go-fast" boats are sometimes damaged when they hit a wake. When the prop comes up out of the water there is no load and the motor speeds up. When the over-rev'd prop slams back into the water it breaks stuff - usually the prop shaft. I think it's possible the stress of returning to the water did some internal damage.

 

[acolic]

Ok I found a compression tester.

From the top cylinder down the compression was 95, 0, 95.

I tested the middle cylinder a number of times.

How can the middle cylinder have zero compression?

What’s that telling me?

Thanks

Alex


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[DaleH]

Hole in the block? That cylinder, rings or piston is smoked? Broken connecting rod? Block and internals needs to be integral and if you did jump a wake and the old prop really 'let loose', the high/unrestrained RPMs could have broken something.

FWIW the old late 80s 3-cylinder Mercs of the same HP range were notorious for losing the top-most cylinder, where 1 guy rebuilt that same block -times! Usually those OMC 3-cylinder 70hps were bullet-proof and arguably one of OMC's best designs. But, use or duty cycle can surely still blow one up ...

 

[acolic]

Thanks

I took the cylinder head off and rotated the flywheel and things seemed to be moving fine.

The cylinder head and cover are in the parts washer soaking right now.

Maybe just changing the head gasket and rechecking the compression is the way to go before further disassembly?

What’s the best way to clean all those hard water stains off the head? Dermal and a brass wire wheel?

Alex

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[Pappy]

You indicated that the engine sounded like it was sucking something up. By that do you mean in the prop? Or another way to put it did the engine sound and feel like something was putting the brakes on the flywheel forcing it to a stop?
Take a good clear close up photo of each side of the cylinder on #2. I want to see it. Use light or whatever you need to in order to get good photos. Looks like I already see aluminum transfer on the exhaust side of #2 but the photo is pretty poor.
When you are looking at the cylinder walls on all three cylinders do they all look identical as far as smoothness goes?
Is there anything different about the tops of the pistons relative to one another?

To answer your question #2 cylinder on a 3-clyinder looper is the most sensitive cylinder when the engine is being "lugged". By that I mean a lot of throttle but the boat is not on plane. That scenario places the engine in a high throttle angle/high ignition timing/low RPM load.
What boat and what prop is on it? What was your load onboard the day the engine quit?

 

[acolic]

Well the story is not great.

I decided to see if I could push a feeler gauge between the cylinder wall and piston.

For the #1 and #3 piston I could not

With the #2 piston I could in multiple spots. I am assuming the gap is not a good idea.

So I have taken off the cylinder cover, removed the carburetors, rotor, stator and all electrical.

According to my manual I should be able to lift off the crankcase from the lower unit and split it.

At that point is it as simple as removing the #2 connecting rod from the crankshaft, pushing the piston out and replacing the piston rings?

With the assumption the #2 piston and cylinder wall is fine etc.

Besides gaskets anything else a must change at this point with the engine in pieces?

Thanks

Alex


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[CedarRiverScooter]

Honrstly I think you are better off finding a donor power head. There will be worn areas in your motor, that once disturbed, will haunt you later..

 

[acolic]

Honrstly I think you are better off finding a donor power head. There will be worn areas in your motor, that once disturbed, will haunt you later..

Unfortunately I’m stubborn.

Couldn’t get the piston out because I didn’t have a 12 pt 5/16 socket to remove the connecting rod bolts.

Any idea if this part is replaceable?

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[acolic]

I found a 1977 75 hp powerhead.

Will that fit on my 77 70 hp lower unit?

Thanks

Alex


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[Pappy]

The answer is yes it will.
You decided to not take the photos of the cylinder walls?
I gave you a lot of information to go off of in looking at your cylinders and it seems to have been ignored altogether?

 

[acolic]

Sorry I wanted to get the piston out so I could take a picture of the entire cylinder wall.

Not ignoring your advice just trying to get a good picture.


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[nccatfisher]

One thing for sure you don't mind jumping into something. You may have jumped way into this one much farther than you needed to.