Replacing head 1971 Evinrude Lark 50 HP

[jfl1960]

I had to replace the temp switch in the head because it shorted out and I had a spare from the previous owner of this motor so I decided to also remove the head to get a good look inside the cylinders at the walls, pistons and combustion chamber on the head, what I found wasn't what I expected, the pistons and rings are in great shape, the cylinder walls have some minor scoring but nothing that warrants a re-bore at this time, but the head itself is severely pitted in the upper combustion chamber (I suspect from a lean condition and detonation), I purchased a replacement used head and am about to install it but I have a question before I do that. The inside of the combustion chamber on the new head has a brown paint or powder coating, as a matter of fact all the internal pathways for coolant along with the combustion chamber have this coating and everywhere except the combustion chamber the coating is pristine, the combustion chamber has approx 80% of the coating gone and raw metal showing, I have cleaned all the carbon off the head and am wondering if this coating MUST be replaced or totally removed or "USE AS IS"???

Here are some pics of my parts last question is the head gasket doesn't fully align with the water pathway should this be trimmed for better flow?

 

[racerone]

The damage on the cylinder head clearly indicates that the motor has been apart and at least the upper piston was replaced.----The scoring is a concern to me. Perhaps not to others !!

 

[jfl1960]

Added some more pics to original post please take a look, thanks.

 

[racerone]

Blocks were coated when new to prevent / slow down corrosion.----Nothing to worry about after 45 years. Not to worry about gasket alignment if you have the tab at the top lined up.

 

[jfl1960]

The damage on the cylinder head clearly indicates that the motor has been apart and at least the upper piston was replaced.----The scoring is a concern to me. Perhaps not to others !!

Hmm I assumed that or the head had been replaced at some time, the main case has never been separated as the paint is still intact at the main case seam and the bolts have no evidence of ever been touched so that leaves the head itself which did show evidence of being off at least. This motor came from an uncle that recalls a stripped spark plug hole back in the late 70's or early 80's, I think the repair guy he used just swapped in a head he had with good threads but pitting in the combustion chamber, don't ask me why they would do that all I know is the mechanic was a back yard jack of all trades type of MacGiver guy and seems a lot of stuff like that happened back in the day, the motor wasn't used since 1985 or so and has sat in my uncles garage ever since until 2 summers ago, once I cleaned the carbs and lubed everything up it started up fine and compression was between 120 and 130 on both cylinders before I opened it up that is why I didn't think the scoring wasn't all that bad. I will recheck the compression once it's all back together. The overheat warning was buzzing all the time and the auto choke wasn't working that's what lead to the strip down, to replace the temp sensors in the head and exhaust covers, now I know the exhaust one was a waste of time as there was a service bulletin that omitted this sensor.

 

[jfl1960]

Blocks were coated when new to prevent / slow down corrosion.----Nothing to worry about after 45 years. Not to worry about gasket alignment if you have the tab at the top lined up.

One last question, the manual says to coat the head gasket with a sealant (evinrude trueseal or sureseal I cannot remember the exact name) but the gasket had "Do Not Use Sealant" stamped on it, did the material in the gasket change and now it seals itself or did the sealant cause future problems????

 

[Faztbullet]

The new gaskets are silicon impregnated and seal with heat, the older gasket needed the peanut butter sealer...

 

[HighTrim]

The NEW gaskets come with sealant on them, as you found. No extra needed. The original gaskets were dry, and would require sealer.

 

[F_R]

Not knowing the complete history on this engine, but I will say without a doubt that battered head has been on an engine that suffered catastrophic piston damage. Since your piston is not battered, the only logical explanation is that the head was previously on some other engine. OR it happened on yours and the piston has been replaced, but you say it has never been apart. OR, the entire powerhead has been replaced, less cylinder head. So, take your pick.

Whatever you decide, that damage is classic. I've personally seen it lots of times.

 

[jfl1960]

The head is back on and I will be mounting the powerhead tomorrow hopefully, thanks for the info guys it's nice to be able to access experience like this especially on such an old motor. Will be back with more questions I am sure.