1975 Evinrude 9.9hp new head gasket help

[Donvirude1975]

Hi guys, I bought a 1975 evinrude 9.9 as a project for my hunting boat. the motor started fine, but after running for a little bit i noted water starting to leak out around head gasket area. i ordered new head gasket, thermostat, and thermostat cover gasket to fix the problem. Once disassemble the head i saw that the previous owner has taken out the thermostat. i have a couple question regarding the reinstallation process.
1. should i replace the thermostat or just leave it out. will it hurt the engine if running without the thermostat.
2. what grid of sand paper should i use to refinish the gasket surface, and do i need to use permatex or just the gasket itself.

thank you for all your help.

 

[jbuote]

Hey there!
​Not a pro here, but if it's supposed to have a thermostat by design, then I'd say put it back in..
​If you leave it out, the engine might run too cool and not get to full HP..
​I suppose in really warm water that might not be a big issue, but in the long run, I tend to vote for putting things back the way they were supposed to be if practical.

As for refinishing..
Not positive, but super fine grit like 320 or greater.. (If memory serves properly.. )
​Use a flat piece of glass or similar HARD surface without pitting and move the part in a figure 8 pattern until all spots are equally shiny..

For permatex or not...
​Definitely not if the gasket itself has "no sealer" or something like that printed on it.
​If it doesn't have that, then I guess it's up to whatever the factory service manual calls for.
Unfortunately, I don't know the answer to that one.. lol

Hope it helps, even if just a little..

 

[Nicktr23]

1. Replace the thermostat. It will help regulate temperature of the motor. The motor operate better at certain temperature, without thermostat, at cold start, it'll take longer to reach optimal temperature.
2. New head gasket already come with sealer. No need to use anything else. Make sure that the cylinder head is flat. Torque to spec. I have 18 hp evinrude, it was 15-18 ft lb. Do not over tighten as you can strip the hole.

Good luck!

 

[F_R]

Torque is 12-14 ft lbs (145-170 inch pounds) Use an inch-pound wrench for better accuracy

 

[tomhath]

When it has a thermostat you won't see water coming out the exhaust on a cold start until it has warmed up, it usually takes about thirty seconds for the thermostat to open.

If you haven't already done so you should also replace the water pump impeller with a good OEM part. Even if the old one was pumping and the seller swore it's like new, you don't really know how old or what shape it's in.

 

[oldboat1]

really need to pull the head cover to do a good job -- t.stat and cover comes off with the head cover. Head cover itself is a little tricky: Lower bolts remain in the cover for removal and replacement -- will need a new head gasket. With the head cover removed, work on the t.stat on the workbench. Resurface both the t.stat and head covers for reassembly (I use 400 grit wet/dry paper on the top of my table saw -- some use a pane of glass for a flat surface).

 

[Donvirude1975]

thank you for all of your inputs. i re-finished both cylinders head gasket and thermostat cover housing surfaces, 400 grit sandpaper on glass table top and will re-assemble it tonight. will up update the result.

 

[raczekp1]

with my expirience doing the falening is less accurate then in machine shop.
they usualy remove 0.30 mm

 

[Joe Reeves]

(Thermostat Purpose)
(J. Reeves)

Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperature to compensate for the distortion.

With the thermostat removed, the difference in temperature between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder, or vice versa. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.

The thermostat in your car isn't there simply to have the heater function properly..... think about it.

 

[Donvirude1975]

thank you for all your inputs. i got everything back together and it ran pretty smooth. the only thing i noted was that there is still a little water leaking out the bottom of the thermostat cover, even though i had the matting smoothed out pretty good. i guess at some point the motor was overheated cause the gasket surface was really uneven when taken off. i guess i will have to use some permatex, as i don't want to take the piece to a machine shop to get it re-surface.

 

[oldboat1]

The bottom of the t.stat cover is the weak spot. Later models (about '85) added an extra bolt down there, and that helped. If you can loosen the bottom bolts a little with a box wrench, work in some permatex, then retighten, that might get it. The gasket can be a problem too, but the only way to correct that is to pull off the whole assembly again and replace the gasket. When they relocated the thermostat to the top of the head cover, the issue(s) finally went away.

 

[Donvirude1975]

it was a new gasket that i just put on, so i will have to pull the thermostat cover off again to re-seal it. thank you for your input.

 

[racerone]

I believe on these motors that water comes out the tell tale right after start up.----The thermostat is NOT in the picture.