1979 15 horse Evinrude loss of power

[seal2127]

I have a 1979 15 horse Evinrude and it has lost alot of power so i checked the normal thing that you guys recomend in other posts got spark and fuel is fine i did a compression test and i am getting 30 on the top and 95 on the bottom my question is what should i do how far do i need to take it down and is it worth it ? thanx for your time

 

[kenmyfam]

Re: 1979 15 horse Evinrude loss of power

I have a 1979 15 horse Evinrude and it has lost alot of power so i checked the normal thing that you guys recomend in other posts got spark and fuel is fine i did a compression test and i am getting 30 on the top and 95 on the bottom my question is what should i do how far do i need to take it down and is it worth it ? thanx for your time

Well hopefully you have a stuck ring or a blown head gasket. How do the spark plugs look when compared to each other ??
How long since the last decarb ??

Welcome to iboats.

 

[bktheking]

Re: 1979 15 horse Evinrude loss of power

Pull the head and look at the condition of the head gasket to start.

 

[1946Zephyr]

Re: 1979 15 horse Evinrude loss of power

30 psi on the top? ouch. I would check and make sure you didn't score a piston. Scored pistons can make a rin stick in the grove and give you lower readings.

 

[mikesea]

Re: 1979 15 horse Evinrude loss of power

id bet on a blown head gasket,thing then is why did it blow,did the eng.overheator do you know if it did or not,as already suggested,pull head and look at cylinder walls for scoring,if all looks ok,you need to put a new headgasket on,be sure to torque the bolts a little at a time til yu get to proper torque,be sure your eng is pumping water ok,those engines are prone to a couple problems with cooling one being the impeller will fail if not changed regularly,the other is a grommet at top of water tube strangles the opening of waterway causing overheat

 

[seal2127]

Re: 1979 15 horse Evinrude loss of power

The water pump is working the two spark plugs look about the same I put new ones in a week or so ago I dont think it has over heated since I have had the motor I will pull the heads and check the gasket and check the cylinder walls and make sure the impeller is in good condition this week and give you guys an update thanx for your help and quick response

 

[kenmyfam]

Re: 1979 15 horse Evinrude loss of power

Good Luck. Let us all know how you make out.

 

[seal2127]

Re: 1979 15 horse Evinrude loss of power

So I took your advise and did the whole decarb thing before i took the motor apart and no change in psi so i took it all apart the head gasket look to be ok not realy sure what I am looking for the cylinder walls on the bottom cylinder look good but the top cylinder has some issues I have enclosed some pics if you guys can let me know what I should do from here that would be great

 

[kbait]

Re: 1979 15 horse Evinrude loss of power

I'm no expert, but if you put it back together w/new gasket and have a reliable compression tester, 30psi would mean damage on that top cylinder. I've never rebuilt one, but I'm sure the work hours would be substantial..

 

[bktheking]

Re: 1979 15 horse Evinrude loss of power

Run your fingernail along the cylinder surface of that top cylinder to check for grooves in the cylinder wall. You might be dealing with either a stuck ring or a broken ring, usually when the rings break they score the cylinders, hence why i'm telling you to check.

 

[bktheking]

Re: 1979 15 horse Evinrude loss of power

Kbait, they are a piece of cake to rebuild, 2-4 hrs tops depending on how many parts you replace. I did the rings and all gaskets on my 9.9, I was shocked at how simple they are!

 

[seal2127]

Re: 1979 15 horse Evinrude loss of power

I prob should have said what is in the pictures that black thing at the bottom of the top cylinder is a little divot other than that it is good not sure how it got that huge divot

 

[Chinewalker]

Re: 1979 15 horse Evinrude loss of power

It looks like you lost the bottom wrist pin retainer ring, allowing the wrist pin to drop down and drag into the cylinder bore. It does not look like something you can hone out. If the divot is less than .015" or so, then you might be able to rebore it and install .030" oversize pistons. Any more than that and you're into a new block. Might be time to call it a parts motor at that point...

 

[bktheking]

Re: 1979 15 horse Evinrude loss of power

And at that point, reboring with new rings and piston is far more expensive than a used powerhead. Strange though, those piston pin retainers rarely break, just bad luck I guess.