Engin Basement Gasket leaking

Plandeck

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I've got oil leaking out around the engine basement gasket on my 2007 8hp Nissan outboard...so replacing the gasket do you recommend using a sealant in addition to the new gasket?
 

Plandeck

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Your sure just the new gasket will do the trick? I'ld hate to have to do it again. The oil leaking transpired after an all night ride using the motor...do engine basement gaskets fail often?
 
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Sea Rider

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Is that a 2 or 4 strokes OB ? You should re torque powerhead on its base from time to time, bear in mind that with heat gasket compresses, if not well re torqued after hours of use, will have water flooding, exhaust fumes, oil onto pan. If the gasket is alum type and has a factory sealant adhered to it, no need to use any other sealant, say mega grey silicone. If it's cardboard you better apply at both sides. Just a light coat. Clean both mating surfaces immaculate clean for a perfect gasket seal.Torque well.

Happy Boating
 
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Plandeck

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Had a very good season with my 8hp 2007 Nissan outboard converted to an inboard 2 seasons ago....however engine basement is still leaking oil which I can't seem to stop...but now I am also showing corrosion on the lower unit...I installed 2 large anodes at the bottom of the unit at the start of the season, but this did not seem to stop the corrosion. the boat sits on a mooring away from any dock, so what could be causing the anodizing?
 

Sea Rider

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Did the lower base gasket changed was alum with sealant on both sides ? If it was plain carboard like need a sealant on both sides. Anyway, both need to be retorqued after 1-2 hour use, retorque lower head bolts tight. Will be surprised on how much they cede with high temp..

If not gasket will be burned around exhaust port area, When installing new base gaskets mating surfaces must be immaculate clean and even at both sides or gasket won't sit flat as expected.

Clean/polish lower tail anodes frequently, if possible leave lower leg raised out of water.

Happy Boating
 

km1125

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Are you sure it's the base gasket? On my Nissan 6HP, the base gasket would only cause an exhaust or water leak. The shaft seal could cause an oil leak, or the oil pan gasket, or the oil pump cover O-ring (which I did have to fix on mine)

EDIT- OK.. strike most of that. I realize that your motor is quite different from mine but thought there might be a similarity here. I just looked at the parts diagram and was thinking the only way the basement gasket could be an issue is if the lower crank seal also had an issue.... until I saw the oil pump pickup screen.
 
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km1125

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....with my 8hp 2007 Nissan outboard converted to an inboard 2 seasons ago....

That should be a whole thread in itself, as I'd be interested in the "how's and why's" of that story.

Back to the gasket issue though... I agree with pvanv... you should not need a sealer on a new gasket. Just make sure the surfaces are clean and with no nicks or imperfections.

If re-using an old gasket, clean it well and then use some Permatex Copper spray gasket on both sides. (I'd rather go the 'new gasket' route, but sometimes availability is an issue)
 

Sea Rider

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It's near impossible to clean and re use and old cardboard type gasket, will be found dried and definitely strongly adhered to mating surfaces, when removing will break in pieces. Base, thermo, cylinder head gaskets are a must have at hand, don't waite the last minute to get them...

Happy Boating
 

pvanv

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Luis, The MFS8/9.8 uses a metal base gasket to join the block to the exhaust housing. That housing also has the sump for the oil pickup. There are no cardboard-type gaskets used there. They pretty much never leak, so plandeck obviously has a larger/different issue. Could be a head gasket leak, a rocker cover leak, a crack in the drive shaft housing, etc.

If you recall, this was that difficult, custom conversion to inboard use.

If there is a lot of corrosion, the boat is either in a "hot" slip, or the charging (or shore power) system is leaking AC to the engine ground. Aside from that, such as on a mooring, it's possible that the wrong anode alloy is being used. Magnesium for fresh water, aluminum for brackish, and zinc for salt.
 
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km1125

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That should be a whole thread in itself, as I'd be interested in the "how's and why's" of that story.

I went back and searched and think I found the original thread. Interesting. To the OP: you should update that thread with some pictures (or put a new thread with the story)
 

Plandeck

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Thank you Paul and the rest of you Admirals...I did use an aluminum anode and I'm in great lake fresh water so maybe this is the problem...will change the anode to Magnesium...but about the ground leak...how would you chase this down?

And the basement leak...I replaced the gasket which is indeed not paper but aluminum, and I used high temp gasket silicon both sides last spring and she still leaked all summer. This is a shame in the great lakes because it goes into the bilge and pumps out into the lake eventually...lousy having a sailboat with an oil slick...wish I could solve this problem because the motor otherwise runs great...pretty sure its not a crack in the casing of the lower unit...replaced the head gasket 2 seasons ago...have been diligent in torquing bolts...she still drips drips drips from somewhere...the problem is that inspection from below the motor is difficult because it is installed as a saildrive. The oil just ends up dripping down the lower unit into the bilge and I can't seem to find its origin, even using a mirror below. The problem only started after an all night ride running the motor at high rpms (wind in the wrong direction)...so maybe its a cracked ring or something similar but I can't think what...again this is a shame because converting the outboard that hung off the back of my sailboat to an inboard saildrive was one of the best moves I ever made.
 

Plandeck

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...I also replaced the oil pump, gasket and o-ring 2 seasons ago...did not help
 

pvanv

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You want a magnesium anode in the Great Lakes.
You were not supposed to use any sealant on the metal gasket.
You must identify the source of the oil leak in order to fix it; otherwise you will be changing each and every gasket and seal on the motor.
Make sure the oil drain plug has an aluminum gasket, and is tight.
IIRC, you built-in the leg (above the lower unit), so the LU has nothing to do with a drip from above.
There are few gaskets involved: Head gasket, Oil pump gasket, Rocker cover o-ring, Base gasket.
There is a drive shaft oil seal, but if that leaked, the oil would come out near the bottom of the drive shaft, and probably be seen near the water pump, where the LU attaches.
There is a cam shaft oil seal, but if that leaked, oil would be all over the head.
The crankcase itself is sealed with high temp silicone, so if that leaked, you would have oil all over the block.
 

Sea Rider

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All main gaskets such as exhaust cover, cylinder head, thermo and base gaskets needs to be retorqued to specs preferably with a torque wrench soon after break in period has ended or when changed for new ones, you'll be surprised on how much they cede, compress with heat and use. Torque tight with wrench base gasket's lower bolts, I'll bet all are out of tight adjustment, check....

Happy Boating
 

Plandeck

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must be the cylinder head gasket or rocker cover o-ring...replacing these very challenging? would you use sealant with the rocker cover o-ring? Looks like the easier of the 2 jobs...how likely is the head gasket to leak? rather not mess with all those torqued bolts etc...
 
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Sea Rider

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If you haven't retorqued lower base gasket from new or when last changed, with heat gasket will become loose, adjust lower bolts with wrench tight till bolts doesn't budge any further, don't worry, won't break them.

Happy Boating
 

pvanv

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must be the cylinder head gasket or rocker cover o-ring...replacing these very challenging? would you use sealant with the rocker cover o-ring? Looks like the easier of the 2 jobs...how likely is the head gasket to leak? rather not mess with all those torqued bolts etc...
No sealer.
Just a few 6mm bolts (10mm heads).
 

Plandeck

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I'll try the retorquing...but on the matter of corrosion to the lower unit now operating as a saildrive, could the copper additive to the bottom paint be setting up a dissimilar metals situation to cause the aluminum corrosion? I did paint the lower unit with the copper additive ablative paint in part to keep zebra mussels from clogging up the water pump intake...that happened one year severely restricting the water flow into the motor. What paint would you recommend using on the lower unit?
 

pvanv

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You're kidding, right?

You must not ever use copper bottom paint on an aluminum LU. You created a battery, with the aluminum failing first. Now you will need to sandblast the LU clean to fresh metal, possibly etch it using a 2-stage chromic acid etch (such as West System sells), and give it two good coats of epoxy. That will be a chore, as you don't want to sandblast the prop shaft, etc., but you do need to blast the prop, the prop shaft housing, and the LU casting itself, plus any of the driveshaft housing that is immersed all the time.

You can then use a long-life specialty paint such as Coppercoat (which is in fact copper, but will be isolated from the aluminum by the epoxy), or Pettit Ultima, Pettit Hydrocoat Eco, or Interlux Pacifica or the old standby aerosols of Pettit PropCoat, Pettit Alumispray or Interlux TriLux 33.

The water inlet strainers are plastic, so the paint may or may not stick to them. Scrape the zebra mussels off the strainers periodically with a piece of wood.
 
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