70 HP Evinrude 70773S Motor issue

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Oct 11, 2013
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My 70hp Evinrude 70773S recently lost power while on the water. I checked compression and am only getting 60 psi out of the top cylinder. What are some things to look for in figuring out what needs to be repaired, I'm thinking the head gasket is a good place to start if everything in the powerhead checks out fine.
 

boobie

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Re: 70 HP Evinrude 70773S Motor issue

Pull the head and see what you find. What did the other cyl's have for compression ??
 
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Re: 70 HP Evinrude 70773S Motor issue

Checked compression again this morning and found all three cylinders running low. Cylinder 1 is at 60 psi, Cylinder 2 is 50 psi, and Cylinder 3 is at 10 psi.
 
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Re: 70 HP Evinrude 70773S Motor issue

Pulled the head off and found the gasket bubbled up and light scratching in cylinders 1 and 3, cylinder 2 is still smooth. Is there anything else to look for? When I was turning the flywheel by hand all 3 pistons were moving correctly in sequence
 

F_R

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Re: 70 HP Evinrude 70773S Motor issue

Any evidence of water ingestion into the cylinders? Looking as though the pistons and head have been steam cleaned is a dead giveaway. Has it ever been overheated? Lastly, rings could be carboned up, something you can't tell without considerable disassembly. 10psi is next to nothing. Something is terribly wrong, or the gasket is completely blown out.
 
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Re: 70 HP Evinrude 70773S Motor issue

The motor did overheat when it died on me as far as water in the cylinders I would think not with all the carbon build up I found shaking loose when I was pulling it apart. I am ordering a new water pump as well just to be safe once I get the powerhead fixed. Anything else yo look for and what should I use to clean these parts up as I go through the motor?
 

boobie

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Re: 70 HP Evinrude 70773S Motor issue

Could you post a pic of the head gasket and the cylinders ??
 
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Re: 70 HP Evinrude 70773S Motor issue

Ok here you go, the head gasket is definitely bad.
 

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F_R

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Re: 70 HP Evinrude 70773S Motor issue

Do whatever you think best, but I'll bet the exhaust cover baffle plate is warped from the overheat. That will allow the gasket to leak and squirt water into the cylinders, destroying everything. When you get the exhaust cover off, you will be able to see what kind of damage the heat has done to the pistons & rings (at least on that side). I'm betting it won't be pretty.
 

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Re: 70 HP Evinrude 70773S Motor issue

I've got most of the bolts off of the exhaust cover baffle except for the bottom two, is there a trick to taking the case off or loosening it to get to those two bolts in order to completely pull the exhaust cover baffle off?
 

boobie

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Re: 70 HP Evinrude 70773S Motor issue

Drill some holes in the lower cowling in line with the bolt heads. When you're done, get some rubber plugs for them. I've done it before.
 
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Re: 70 HP Evinrude 70773S Motor issue

I actually was able to get the case off and get the baffle off, the piston are scratched pretty bad on the top two cylinders. I'm debating on whether or not to go ahead and get 3 new pistons and getting the cylinders or refinished or could I go ahead and run the motor once I get the gaskets in and put back together?
 

boobie

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Re: 70 HP Evinrude 70773S Motor issue

Could you post a good pic of the top 2 cylinders ??
 
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Re: 70 HP Evinrude 70773S Motor issue

1380062_10201225363978886_345410612_n.jpg

Sorry it took so long to get this pic up but I'm figuring it's going to need new pistons.
 
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