# EXHAUST MANIFOLD GASKET REPLACEMENT



## scoobeb (Jul 2, 2016)

I have a 1993 20hp 2stroke mercury in pristine condition.It has i believe an original exhaust manifold gasket and the one behind it that i'm not to sure the name of it,sorry.

My question is everything looks great,motor runs perfect but do i need to replace that as routine maintenance because i don't think it ever has been.I just have read stories about the bolts breaking off,etc..I can tell you the motor has never seen saltwater if that helps and has extremely low hrs on it.I did most of the other maintenance stuff on it but have never changed one of these,doesn't look to hard but i know the old saying is leave good enough alone.Amy help on this would be great,thanks.


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## scoobeb (Jul 2, 2016)

I guess this would be a much easier question to ask,besides the impeller and lower unit oil and plugs what other gaskets need changed if any like the exhaust manifold gasket I'm asking about or the gasket that sits over the cylinders to the power head. Does any of that need changing or should it last until any issues occur or the life of the engine as long as it's cared for propel as in completely flushed every time,and engine cleaned up good . I just want to know if anyone changes the manifold gaskets, etc.... thanks.


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## Johnny (Jul 2, 2016)

Scoob - do you have a service/parts manual for your motor ??



.


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## dahut (Jul 2, 2016)

At times like this, I like to ask the most basic question of all:
"What does the manufacturer recommend?"

I'm anything but an expert, but I doubt the exhaust manifold gasket is considered an element of routine maintenance.

In fact, just taking things apart because you can presents its own problems. Unless you suspect a leak or other failure of the gasket, or need the manifold exposed to make repairs or clear it of some obstruction, the gasket is probably left well enough alone.

Sent from my LGL31L using Tapatalk


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## JMichael (Jul 2, 2016)

If it ain't broke, don't fix it. I'm no professional either, but I've never heard of replacing a gasket at certain intervals or as a maint item. And I've never replaced a gasket that wasn't disturbed (disassembly doing repairs etc) or has not failed. I'm not saying that there isn't a situation where you would, but I've never heard of one.


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## KMixson (Jul 2, 2016)

I would not change the gasket unless you think it is leaking or you remove the exhaust manifold for some reason. It can become more work than you expect if you accidentally break a stud or bolt. Then you will have a much harder time getting it back together. Exhaust studs and bolts are very prone to breaking when trying to remove them. Case in point, I was removing my exhaust manifold on my personal vehicle and broke a couple of studs. As I tried removing the broken studs I ended up having to drill them out. As I was drilling one out I accidentally drilled too far into the head and hit the water jacket. I ended up reinstalling the manifold and using a bolt in that hole and with the bolt torqued down it does not leak. I got lucky there. That was 10 years ago and it still has no coolant leaks as I can see. Just remember be prepared for the worst if removing an exhaust manifold.


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## scoobeb (Jul 6, 2016)

According to what i have read it says to do it every 8yrs or so but i believe it's the original of 24yrs old and no leaks.The lower unit when i took it off was flawless with no corrosion and also the thermostat cover came off easy.I would suspect that the bolts would come off easy but i guess i will leave it alone since no leaks.The bolts look like they have never been taken off.


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## perchjerker (Jul 6, 2016)

just leave it be

didnt you learn anything from your last broken bolt episode? lol


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## JMichael (Jul 7, 2016)

perchjerker said:


> just leave it be
> 
> didnt you learn anything from your last broken bolt episode? lol


I wasn't gonna go that far, but since you said it.........Ditto! :mrgreen:


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## scoobeb (Jul 16, 2016)

JMichael said:


> perchjerker said:
> 
> 
> > just leave it be
> ...


That was a fluke accident and yes I shouldn't of messed with it,but this is a maintenance part or gasket from what I have read and actually waiting for it to leak is not the brightest idea. It says from all the research I have read it usually should be changed every 8-10 yrs just as a maintenance thing but most people don't do it. If it does leak by chance it says it can be catastrophic. So now you still think after 24yr it shouldn't be replaced even if it's not leaking ???? I want your serious answer to on that,24yr it hasn't been done,maybe this is a gasket that lasts the life of the motor if their is such thing. That last episode was a fluke accident and partially my fault for forcing the bolt in sideways and cross threading it. Maybe I will just leave it but I just hope it never leaks because bad things can happen,that's all I'm saying. Also the bolt that I screwed up was on a totally different outboard, every bolt ,screw or anything I have loosened on the 93 merc has come out like butter,I mean easy,including the thermostat housing which is usually another bad area for broken bolts. I understand your logic, if it ain't broke then don't fix it. Has anyone changed that gasket here even know it's never leaked or do you guys just leave it???


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## JMichael (Jul 17, 2016)

Keeping in mind that I'm not a professional (although I was employed as a professional auto mechanic for a period and I've worked on all sorts of engines in my life), as far as I can remember, I've never replaced a gasket that didn't leak or has not been disturbed/disassembled. Maybe things are different for outboard motors. They might replace it while in there working in the area maybe, but I've never heard of opening up a motor for the explicit purpose of replacing a gasket. Now, Pappy is here and it would probably be considered careless not to seek his opinion since he is a professional, if you really want the correct answer.


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## perchjerker (Jul 17, 2016)

if your research says change it, and you think you should change it, and if it makes you feel better change it, if it makes you sleep well at night...

then change it!!!

you dont need us to tell you what to do.


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## scoobeb (Jul 17, 2016)

Not once did i ask you to tell me what to do,i asked for opinions and only opinions only.I just wanted to know what everyone did or does on this matter. i wanted to see if anyone changes them which it seems they don't.That is good enough for me.


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## scoobeb (Aug 7, 2016)

Well after some more serious reading i'm still contemplating on doing this or not.I was hoping for someone with a ton of experience with these outboards can chime in on this.I know of the 2 different blocks as i have mentioned in another thread,there is a post 94 Mercosil block that seemed to be the powerhead more prone to water intrusion in the number 2 cylinder from manifold gasket breakdown then there is the pre 94 Nikasil block which seems to have very little issues on this which i have but it still makes me weary.How long could a exhaust manifold gasket hold out?Some people say to 100% change it and some say to leave it alone if it's not broke but i still have to keep in mind it is a 24yr old outboard.It looks to have extremely low hrs but i don't know exactly how many and it has no corrosion whatsoever so that also tells me it hasn't been ran in saltwater.Should i just leave it alone if it's not leaking water at all or in the cylinders?

Please,i'm looking for some facts here not just estimated guesses.I'm hoping some people with many yrs experience or that has ran these type of 20/25hp mercs can chime in with their thoughts or experiences,thanks.I'm just not sure if this is a maintenance thing or a fix by issue thing that is my biggest concern.


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## KMixson (Aug 7, 2016)

Apparently you are not going to be happy until you change the gasket. If it lets you sleep better change it.


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## scoobeb (Aug 7, 2016)

Again,it's not about that,I'm looking for people with experience with this particular outboard to see if any other people change them as a routine maintenance thing or is it a if it fails type of deal then worry about it. I rather leave it alone if I know it really doesn't have to be changed. I just want reassurance that it doesn't have to be changed unless it fails. I have fear of breaking bolts,that is my biggest issue or I would of changed it already,but if someone with this motor tells me different that actually owns or works on these then I won't mess with it. Nothing wrong with being over cautious about something imo.


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## muddywaders (Aug 7, 2016)

Have had this gasket fail on a 93 20hp merc luckily it was an external leak.Not sure why it failed not corroded and was never overheated.Same problem with a newer yamaha mating surfaces perfect but break in gasket.How would one detect an internal leak?excessive steam?rough running?washed piston crown or plug?powerhead damaged by that point?So yes change the gasket the merc ones are cheap.Be gentle when removing bolts as you probably already know use a small wrench and if you suspect one is frozen drill the head off.Once the manifold is off you can apply heat and penetrating fluid.Weld a nut or use vice-grips to remove remaining bolt.


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## scoobeb (Aug 7, 2016)

Ty,someone with an honest reasonable non sarcastic answer. Here is what I know about this engine. I got it around 8 months ago,I replaced nearly everything I believed to be a maintenance priority. So,I believe everything on the motor to be original except the impeller and someone decided it was a good idea to run it without the thermostat in it. So,I checked compression first of course, 120 lbs on both cylinders which you can't get any better,here is a list on all I replaced less than 4 months ago, 2 brand new coils,2 brand new wires,2 new plugs,new thermostat and gasket,new line from thermostat to pee hole, new complete water pump, I mean impeller, gaskets, washers, key, housing, metal plate,everything, new synthetic lower unit oil and drain plugs with gaskets, carb cleaned spotless as well as a complete rebuild of all new parts, brand new fuel assembly including filter and gas lines, brand new fuel tank and line, prop and pull cord. So this motor is in A 1 running condition and no signs of any water intrusion on the plugs or under the cowling but again it's a 24yr old outboard and I don't know how it was cared for in the past,so knowing all this info now and how great it runs should I go that step further to replace those 2 gaskets or leave good enough alone???? I also use non ethanol fuel with ring free and lucus fuel conditioner, the green stuff from Walmart and it seems to work great. I just don't want to mess with it if that particular gasket will continue to hold up. Owner claimed it has less than 25hrs of freshwater use as it sat in a barn most of it's life but it runs I mean like a rapped ape,powerful and fast. Taking 9 bolts out I guess just makes me nervous if I really don't have to,I could just run it and keep an eye on it to. If I do decide to replace them do I need any special gasket sealer or just replace them both and done? Now what do u think????


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## Johnny (Aug 8, 2016)

Scoob - upon changing the head gasket on my '79 Johnson,
the replacement gasket was something I had never seen before..... 
it had a very slick feeling like wax or silicone.... years before, 
they were just the plain gray dry gaskets that you applied sealer with. 
I called the distributor and he said that with the "new and improved" gaskets
that feel like wax or silicone, you should not use any type of sealer.
the new ones are "self sealing" . . . as he explained it to me.
I guess if you decided to go this route, go ahead and purchase the gaskets
just to have in your parts box.... then, you can come back here and ask about sealeants.
again, the two mating surfaces should be spotless clean and honed on glass or tabletop
hope that helps.


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## scoobeb (Aug 8, 2016)

I ordered the gaskets and 4 extra bolts just as a pre caution just in case I broke some off by replacing them. I still haven't completely decided yet if I'm going to mess with it,I may leave it as a if it works great,no leaks then don't mess with it if it ain't broke method,lol. No sign of water intrusion or wet plugs or anything of the sought but I just figured 24yr old outboard maybe it should be changed but I'm not quite sure yet. It runs flawlessly so I may just run it all fall and winter here in fl to spring then when it gets to hot in summer I will work on it just in case I did snap a bolt I don't mind it sitting because I hate fishing in heat so I could let it sit with no issues and take my time getting the snapped bolts off,but that is all speculation, all 9 bolts may come off like butter. Everything on this motor looks mostly original as far as exhaust manifold gasket because the bolts are undisturbed, I may just leave good enough alone as it's help up this long,like I said if I do it,it won't be till after next late spring anyways.


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## scoobeb (Aug 8, 2016)

I talked to someone about this who owned his own shop and said he personally had worked on these outboards allot along with tons more of course and I asked him what he thought, he said he has never personally seen one fail in his lifetime and shouldn't unless owner neglect comes into play. He said just leave it be if it runs flawlessly no matter how old she is and if you want peace of mind just pull the bottom plug once a mth to Check for any water on the plug,that would be a good indication of a failed gasket usually,he went on to say he would bet the original gaskets would last for the rest of the time I own it and so on till it's retired. He said don't worry and just enjoy without panic. Works for me,just for peace of mind I will check the lower plug once a month,there is no problems with this outboard and I plan to keep it that way. Case closed, I will leave it be. I at least have the gaskets on hand if it does act up. Thanks to all for the helpful info.


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## scoobeb (Aug 10, 2016)

muddywaders said:


> Have had this gasket fail on a 93 20hp merc luckily it was an external leak.Not sure why it failed not corroded and was never overheated.Same problem with a newer yamaha mating surfaces perfect but break in gasket.How would one detect an internal leak?excessive steam?rough running?washed piston crown or plug?powerhead damaged by that point?So yes change the gasket the merc ones are cheap.Be gentle when removing bolts as you probably already know use a small wrench and if you suspect one is frozen drill the head off.Once the manifold is off you can apply heat and penetrating fluid.Weld a nut or use vice-grips to remove remaining bolt.


If I decide to do this do I install the gaskets dry with no sealant of any kind????

2. When re installing the 9 bolts do I put a dab of grease on them to make it easier to go back in and so they don't seize up?????


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