25hp Johnson - exhaust gasket replacement

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Johnny

Well-known member
TinBoats Supporter
Joined
Mar 2, 2014
Messages
3,194
Reaction score
10
Location
Central FLORIDA - The Sunshine State -
My 1979 Johnson 25 has a new head gasket but is still getting water into the cylinders.
sooooooo..... with the information I have gathered here, the bottom must come off
and replace the exhaust gasket.
Does anyone know about how many hours of labor this would take in a professional shop ?
I don't want to undertake this project myself as I am NOT a mechanic.
I can, however, replace the impeller, etc.
But going up into the motor gives me the shivers.

Just asked the local bait shop that has a mechanic that does their work and he is very
dependable but he is out of town this week. his rate is $65 per hour and they have no
problem with me getting all the parts needed and bring the boat to him.

So I am just wondering how long it would take to change out the lower gaskets
without any serious major unforseen problems.
 
Pap, from what I have read here on this forum, if the engine block is ok
and the head gasket fits good and the water jacket is ok,
water can be pulled up from the exhaust tube into the cylinders if the gasket is bad.
so, I am only assuming this is where my problem is.
I have had the head off several times the past few months for one thing or another
and the water jacket is spotless inside. The heads honed smooth, etc.
so process of elimination, and from what others have said here in the past,
is what I am guessing. Red Circle area on attached photo.
When running the motor in a can, water is spraying from the bottom of the
motor bottom pan, which I think is not normal.
Thanks !!
 

Attachments

  • 16.png
    16.png
    204.9 KB · Views: 1,104
  • 04.png
    04.png
    174.9 KB · Views: 1,103
Okay that is your base gasket or powerhead base gasket. Not an exhaust gasket although it would seem a logical name for it.
Although that may need to be replaced for a visible leak I would go for the exhaust side cover gasket as far as your leak into your cylinder goes. Far better chance.
Again...easy to change both of them. Besides the visible leak what is going on with the engine ?
 
Thanks Pap - - -
Yeah, I can do the Exhaust Gaskets. (now that I see what it is)
As for the Base, I will wait until I finish the exh. gaskets first
and see how it goes after that.

Other than that, I put on a complete 35hp carb, reed plate and intake manifold and it
is running a little too rich - (jets need adjusting, I think) a lot of black oil when first
starting up then after it warms up, seems to run smoother. have not had it on the lake
since I have changed out the directional tubes, head gasket, thermostat, and generally
cleaned it all up. oh, and two spark plug thread inserts.
I ran the motor in a can for about 10-15 minutes at high RPM before I pulled the plugs to check
for water. They were relatively clean but oily - and water droplets.

If it continues to run rough, I will put the original 25hp carb & plates back on which has all new gaskets.
Thanks again
 
yessir, since it has been sitting for a couple of months outside, with all our rain storms,
I did that first - siphoned out the gas to ensure good clean gas + bled fuel lines.

Just removed the exhaust cover (only a bit harder than the head due to bolts being in
hard to get places.

Good news - gasket is leaking - obviously leaking water into the cylinders.
bad news - broke off two bolts, soaking them in penetrating fluid for a few days
while waiting on new gaskets - then will GENTLY wiggle them loose (hopefully)

After removing the bolts, it is obvious problem when the bolts come out rusty
and fouled with exhaust carbon.

did the best I could on the photos

I will ensure very clean and flat surfaces prior to installing new gaskets.
only want to do this ONE TIME.

Thanks Pap for the help.
 

Attachments

  • boat motor exh 017.JPG
    boat motor exh 017.JPG
    230.5 KB · Views: 1,058
  • boat motor exh 014.JPG
    boat motor exh 014.JPG
    50.8 KB · Views: 1,060
  • boat motor exh 013.JPG
    boat motor exh 013.JPG
    98.6 KB · Views: 1,059
  • boat motor exh 012.JPG
    boat motor exh 012.JPG
    199.4 KB · Views: 1,059
  • boat motor exh 011.JPG
    boat motor exh 011.JPG
    56.1 KB · Views: 1,060
  • boat motor exh 010.JPG
    boat motor exh 010.JPG
    82.3 KB · Views: 1,058
  • boat motor exh 009.JPG
    boat motor exh 009.JPG
    73.3 KB · Views: 1,060
  • boat motor exh 008.JPG
    boat motor exh 008.JPG
    60.9 KB · Views: 1,060
Hey Pappy,
in your experience, why would the top exhaust portion have more
carbon deposit than the lower ? is this normal ? or does something need adjusting.

#2. got the two broken bolts out with some heat and vice grips (whew).

#3. when I get it back to running, I will put more exploratory effort to see where the
other water is coming from.

Thanks again,
Johnny
 

Latest posts

Top