98 200 Johnson cylinder head question
 

I have a 98 Johnson Ocean runner on my boat that I purchased at the end of last season. I did a compression test and it was 100 across the board. I ran the boat twice last year and it ran well. I just finished going through the boat and fixing a lot of little issues with it so I haven't run it yet this year. While changing the plugs I noticed a bit of corrosion where the head meets the block on each cylinder bank. The lower plugs also were rusted. I'm wondering if this is normal or if I have head gaskets that are failing? I plan on keeping an eye on it. My last Johnson had a new power head on it so there was no corrosion. Thanks

It's actually semi normal, and is normally when I do head gaskets.

Thanks for good news I guess. When doing head gaskets on these engines do the heads have to be milled? Do the seals around the water jackets fail before the cylinders? I got this boat for about a third of the price of what I saw them advertised for. It ran great and the compression was even so I figured the engine was good. I definitely don't want to damage this engine.

I don't normally mill the heads unless theres a ned for it. Chances are it will run for a long time ike it is as it isn't uncommon to see corrosion at the seem. When you see rust in the head gasket is when you need to be really concerned. Being a 98 though that is a closed deck block IIRC, and they are more prone to corrosion in the gasket area.

I definitely want to keep my eye on it. My biggest concern is snapping head bolts. That's never fun. Thanks

The stainless head bolts aren't to bad about snapping, but they do get corroded in due to the dissimliar metal problems between stainless and aluminum. If the gaskets themselves aren't rusty, then I would run it for awhile before messing with it.

Sounds good. Thanks.

Was looking at the heads again today and I think I want to replace the gaskets. I was wondering if you prefer factory gaskets or if you use an aftermarket source.

About the same anymore. Alot of the OEM parts are now being made by teh aftermarket. These old carbed engines have been out of production for so long, that it was well before BRP's time. So they outsource them to the aftermarket, repackage them, mark them up 100%, and resell them as OEM.

i know the head gaskets say no sealent on them but i've always had better luck with them if i spray copper coat on both sides of the gasket and let it dry over before installing them.

I use the black PERMATEX aviation grade sealant that comes in a white bottle, and you brush it on. I've used the EVINRUDE stuff as well, but prefer the PERMATEX aviation sealant.

In searching for the gaskets I found quite a few horror stories about completely rotted out water jackets. Hopefully I won't find that. The engine runs well right now but I'd like to get ahead of a head gasket failure.
Should the head bolts be replaced as well?

If it still has the origanal 98 head bolts, no. They were stainless and outlasted the engines. The 93+ blocks were closed deck lost foam castings, and did suffer from quite ab it of corrosion issues since the design allowed places for saltwater to sit and collect without draining away.

they use to make cylinder caps for those OMC Loopers. it was a SS outter sleeve to replace the rotted out aluminum around the cylinder to head areas.

If the engine had compression that was even across the board would it be ok to assume that it's not corroded?

compresion won;t tell you about internal corrosion, only the condition of the cylinders, unless its corroded all the way thru the cylinders

I should have elaborated. I know that compression tests have no bearing on water jacket condition. What I was asking is if my compression is even across the board would it be safe to assume that the water jackets aren't rotten to the point of no return.
I really already know the answer. I was just hoping that someone would say that when the corrosion gets bad the compression turns to crap.
My engine runs great right now. I just have the visible corrosion at the mating surfaces and I'm a little hesitant in opening up a can of worms. At the same time I don't want to wait too long. Pretty much feel like whichever route I choose I'm going to wind up on the wrong end.

It's a catch 22. These engines are getting old enough that even taken care of engines are getting corroded beyond the point of no return. It is just teh nature of salt water. Your rolling the dice either way.

I'd say if it's running fine run it and leave the heads alone.