Goo in cylinder, crust on plug??

[Slojoe]

1977 Evinrude 70hp starts and runs great. The spark plug on the top cylinder builds up a reddish/white crust, like a calcium deposit, on the ceramic around the electrode. When I burn through around 10 gallons of fuel the deposit gets big enough to kill the motor, so I would clean it off with a knife and go for another 10 gallons. I did this all last summer, running around 200 hours in the ocean with no other problems.

All 3 plugs were burning an even brown, compression was 120+ in all 3 holes. I decarbed the motor then put another 100 hours on it with no change. Then I talked to an old Johnson mechanic who said, deposit on the plug means a head gasket.

Today I pulled the head gasket and this is what I found. Goo in the top cylinder looks like brown vaseline.


The head also had a bunch of the goo in it.


The head gasket looks like it wasn't leaking, both in the pic above and here is a pic of the back side of gasket.


Anyone ever seen anything like this?

Where is this goo coming from? I am thinking maybe the exhaust manifold, maybe the gasket is leaking, the heat of the exhaust is making this goo out of oil & water, then it is migrating into the cylinder? Then combustion causes it to turn into hard crust on the plug?

Or could it be the cylinder cover gasket?

Last bit of info, the center plug was always wet, as if gas fouling, but now I see a little bit of brown goo in the middle cylinder as well, maybe it is the same problem as #1 just not as bad??

I need to figure out what this goo is, and where it is coming from, before taking apart anything else and finding it isn't the problem. Thanks for any help-

 

[Joe Reeves]

Re: Goo in cylinder, crust on plug??

For me, it's difficult to see any problems with the gasket or the sealing surfaces although they may be there... just not clear enough.

If any of the pistons are deteriorating/melting down somewhat, that would indicate a pre-ignition problem which is usually caused by the timing being too far advanced (if you've changed it).

This problem can also be caused by a faint spray of water being forced into a cylinder by a weak area of the head gasket (or from elsewhere).

Clean the sealing surface of the cylinder head and the block, then install a new head gasket. Torque the head bolts to 18 to 20 foot pounds in the following sequence and cross your fingers. Hopefully this eliminates your problem. If not, the next thing to check is the exhaust baffle plate gasket (lg plate on side of PH).

13..14
9....10
5.....6
1.....2
4.....3
8.....7
12..11...Continue on in an every widening circle.

 

[Slojoe]

Re: Goo in cylinder, crust on plug??

Thanks, I cleaned it up and installed a new gasket, used the book to torque it down. I haven't messed with the timing, just do one thing at a time so I know if I goofed. Don't think the pistons are deteriorating, I hope the head gasket does the trick. If not I will try the exhaust plate gaskets... manual shows 3 gaskets, one is nla. Will deal with that later if the problem persists. Kind of afraid to snap off one of those little screws holding the exhaust cover on, motor is 35 years old. Thanks again