1977 Evinrude 85hp - Oil Leaking from Air Silencer Cover

OldOMC31

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My dad has a 1977 Evinrude 85hp that he had since new. Not much has been done to the engine besides replacing impellers a few times and some lower unit seals. He had some issues last summer with leaking fuel. I helped him replaced all of the fuel lines, rebuild the carburetors using OMC kits, and rebuilt the fuel pump using an OMC kit. The diaphragm of the fuel pump had a pin hole which seemed to be the leak issue. Now with everything replaced/rebuilt, and pumping up the primer bulb, there is no fuel leaking anywhere on the engine. Motor has always and still does run excellent.

After this work, there is oil leaking out of the port coming from the lower crankcase. There is a small nipple on the crankcase with a hose going to the lower corner of the air silencer box. I am assuming this always had oil coming to it in the past when tilted up, but now it is dripping out of the air silencer cover halves for about 30 mins after running the engine and tilting it up. My dad had never had oil dripping out of here until this work was done. Boat is stored in a garage, and docked for a week at a time when using it. When docked, the motor is tilted up as the depth of the lake at the dock is shallow. This has been done every summer since this engine was new with no oil leaking out of the air silencer cover.

I removed the air silencer cover after using the boat last time and 2 stroke oil, about 1/2 ounce, would leak out over the course of 30 minutes then quit. Since the cork gasket between the halves of the air silencer cover was original, I assumed this was the culprit. I ordered a new OMC cork gasket thinking this would solve the issue of leaking oil. My dad put in the new gasket this week and said it is still leaking oil after he runs the motor & tilts it up after use.

I believe this port on the air silencer cover is supposed to suck any fuel leaking out of the carbs back into the crankcase to be burnt when the engine is started next. I also am assuming that the 1/2 ounce of oil that drips out of the crankcase is what is coating the bottom end of the engine and when the engine is shut off/tilted up, the oil film on all of the internals is settling to the lowest point (this fitting on the lower part of the crankcase) and the oil is settling into the air silencer cover via the hose connecting the nipple on the lower crankcase to the air silencer box.

The carbs are not leaking any fuel when the engine is tilted up after running. The 2 stroke oil leaking into the air silencer box is blue (Johnson/Evinrude 2 stroke oil) and doesn't smell/taste burnt.

From my research, this cork gasket should not be coated with gasket sealing compound. Am I wrong here? What else can I try to keep this oil from leaking out of the air silencer box.
 

saltchuckmatt

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My dad has a 1977 Evinrude 85hp that he had since new. Not much has been done to the engine besides replacing impellers a few times and some lower unit seals. He had some issues last summer with leaking fuel. I helped him replaced all of the fuel lines, rebuild the carburetors using OMC kits, and rebuilt the fuel pump using an OMC kit. The diaphragm of the fuel pump had a pin hole which seemed to be the leak issue. Now with everything replaced/rebuilt, and pumping up the primer bulb, there is no fuel leaking anywhere on the engine. Motor has always and still does run excellent.

After this work, there is oil leaking out of the port coming from the lower crankcase. There is a small nipple on the crankcase with a hose going to the lower corner of the air silencer box. I am assuming this always had oil coming to it in the past when tilted up, but now it is dripping out of the air silencer cover halves for about 30 mins after running the engine and tilting it up. My dad had never had oil dripping out of here until this work was done. Boat is stored in a garage, and docked for a week at a time when using it. When docked, the motor is tilted up as the depth of the lake at the dock is shallow. This has been done every summer since this engine was new with no oil leaking out of the air silencer cover.

I removed the air silencer cover after using the boat last time and 2 stroke oil, about 1/2 ounce, would leak out over the course of 30 minutes then quit. Since the cork gasket between the halves of the air silencer cover was original, I assumed this was the culprit. I ordered a new OMC cork gasket thinking this would solve the issue of leaking oil. My dad put in the new gasket this week and said it is still leaking oil after he runs the motor & tilts it up after use.

I believe this port on the air silencer cover is supposed to suck any fuel leaking out of the carbs back into the crankcase to be burnt when the engine is started next. I also am assuming that the 1/2 ounce of oil that drips out of the crankcase is what is coating the bottom end of the engine and when the engine is shut off/tilted up, the oil film on all of the internals is settling to the lowest point (this fitting on the lower part of the crankcase) and the oil is settling into the air silencer cover via the hose connecting the nipple on the lower crankcase to the air silencer box.

The carbs are not leaking any fuel when the engine is tilted up after running. The 2 stroke oil leaking into the air silencer box is blue (Johnson/Evinrude 2 stroke oil) and doesn't smell/taste burnt.

From my research, this cork gasket should not be coated with gasket sealing compound. Am I wrong here? What else can I try to keep this oil from leaking out of the air silencer box.
Your outboard should be using pre-mixed 50 to 1 fuel so where is the oil coming from?

It should be mixed oil and gas and it's quite normal to drip out of the carbs when tilted up.
 

OldOMC31

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Yes we are using pre-mixed at 50:1.

Oil is coming from the small hose connecting the nipple on the lower crankcase to the lower corner of the air silencer case. Last time I took the boat out, I removed the air silencer cover when I got back to the dock to see where the oil is entering. No oil/gas came from the carbs into the air silencer case. The oil would slowly drip out of the small hose in the lower corner of the air silencer case for about 30 minutes then quit. Did this 3x times and checked with the same results.

My guess is it did this since day 1, but that air silencer cover has never been off before. Now that we removed it and are having a leak, I figured the gasket was the problem as the old cork gasket was dried out and half stuck to the cover plate. Cleaned up the surfaces of the silencer box and cover and replaced gasket but leak is still there.
 

saltchuckmatt

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Yes we are using pre-mixed at 50:1.

Oil is coming from the small hose connecting the nipple on the lower crankcase to the lower corner of the air silencer case. Last time I took the boat out, I removed the air silencer cover when I got back to the dock to see where the oil is entering. No oil/gas came from the carbs into the air silencer case. The oil would slowly drip out of the small hose in the lower corner of the air silencer case for about 30 minutes then quit. Did this 3x times and checked with the same results.

My guess is it did this since day 1, but that air silencer cover has never been off before. Now that we removed it and are having a leak, I figured the gasket was the problem as the old cork gasket was dried out and half stuck to the cover plate. Cleaned up the surfaces of the silencer box and cover and replaced gasket but leak is still there.
Must be a failed check valve in that line but others will be better able to confirm. Either way it must be gas mixed with oil.
 

saltchuckmatt

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Yes we are using pre-mixed at 50:1.

Oil is coming from the small hose connecting the nipple on the lower crankcase to the lower corner of the air silencer case. Last time I took the boat out, I removed the air silencer cover when I got back to the dock to see where the oil is entering. No oil/gas came from the carbs into the air silencer case. The oil would slowly drip out of the small hose in the lower corner of the air silencer case for about 30 minutes then quit. Did this 3x times and checked with the same results.

My guess is it did this since day 1, but that air silencer cover has never been off before. Now that we removed it and are having a leak, I figured the gasket was the problem as the old cork gasket was dried out and half stuck to the cover plate. Cleaned up the surfaces of the silencer box and cover and replaced gasket but leak is still there.
I'm assuming it's part number 25, 38 and 2 making the connection. Not sure what that does.

I do know that when tilted the floats will allow fuel to pass and flow out the carbs.

Let's see what the masters say.
 

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flyingscott

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What's happening is normal. Replace the line from the nipple to the block. That line is used to reclaim the fuel oil mix that ends up in the air box.
 

saltchuckmatt

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how do you figure it didn't? The hose was there for a reason. Pretty common for them to leak from there. Maybe brush up on how carbs work I think.
In my experience when the motor is tilted gas mixed oil goes into the air box but the OP said it never did before.

Another words you don't need to explain it to me.
 

flyingscott

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In my experience when the motor is tilted gas mixed oil goes into the air box but the OP said it never did before.

Another words you don't need to explain it to me.
Really clearly said the box had never been off before. So ask the op if he has x ray vision. And brush up on how carbs work. And the evaporative properties of gas.
 
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flyingscott

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Yes we are using pre-mixed at 50:1.

Oil is coming from the small hose connecting the nipple on the lower crankcase to the lower corner of the air silencer case. Last time I took the boat out, I removed the air silencer cover when I got back to the dock to see where the oil is entering. No oil/gas came from the carbs into the air silencer case. The oil would slowly drip out of the small hose in the lower corner of the air silencer case for about 30 minutes then quit. Did this 3x times and checked with the same results.

My guess is it did this since day 1, but that air silencer cover has never been off before. Now that we removed it and are having a leak, I figured the gasket was the problem as the old cork gasket was dried out and half stuck to the cover plate. Cleaned up the surfaces of the silencer box and cover and replaced gasket but leak is still there.
Use aviation permatex on the cork gasket. You will probably find the bottom has pushed out causing the leak.
 

OldOMC31

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Gas/oil could have leaked into the air silincer box prior to taking the cover off for the first time. What I was staying is that it has never leaked out of the air silencer cover before.

Now that I have replaced all the fuel lines and rebuilt the carbs and fuel pump (fixing the original cause of the fuel leak from fuel pump) oil is now leaking out of air silencer cover.

This hose from the nipple on the lower crankcase to the nipple on the air silencer was also replaced. When I run the engine now (with the silencer cover installed) and get back to the dock, I took off the cover immediately after and can see the oil coming from the nipple into the silencer box and nothing entering the box from the carb throats. It could have some trace gas still in it but it is way thicker than 50:1 mix.

Regardless of how it gets in there it seems the hose is there to return it back to the crankcase when started next. If it never leaked before and now is we either got lucky for 45 years with the original cork gasket, bent the cover slightly removing it and the new cork isnt sealing properly, or the original gasket maybe had some sealer installed on it.

I've read on here about gasket sealers and thought nothing in front of carbs should be getting sealer as to not accidentally block carb passages etc. if some were to flake off.

What would be the best sealer to try here as we don't like seeing the oil slick in the water coming from the docked boat lately.
 

flyingscott

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Use aviation permatex to hold the gasket in place then torque it correctly. The oil was always in there you just never saw it. ALL carbs leak when you tip the motor up.
 

saltchuckmatt

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Gas/oil could have leaked into the air silincer box prior to taking the cover off for the first time. What I was staying is that it has never leaked out of the air silencer cover before.

Now that I have replaced all the fuel lines and rebuilt the carbs and fuel pump (fixing the original cause of the fuel leak from fuel pump) oil is now leaking out of air silencer cover.

This hose from the nipple on the lower crankcase to the nipple on the air silencer was also replaced. When I run the engine now (with the silencer cover installed) and get back to the dock, I took off the cover immediately after and can see the oil coming from the nipple into the silencer box and nothing entering the box from the carb throats. It could have some trace gas still in it but it is way thicker than 50:1 mix.

Regardless of how it gets in there it seems the hose is there to return it back to the crankcase when started next. If it never leaked before and now is we either got lucky for 45 years with the original cork gasket, bent the cover slightly removing it and the new cork isnt sealing properly, or the original gasket maybe had some sealer installed on it.

I've read on here about gasket sealers and thought nothing in front of carbs should be getting sealer as to not accidentally block carb passages etc. if some were to flake off.

What would be the best sealer to try here as we don't like seeing the oil slick in the water coming from the docked boat lately.
Could be a small crack in your air box.
 

OldOMC31

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Could be a small crack in your air box.
Thanks, I'll check for cracks next time I'm there, but from what I can tell, the gas/oil was leaking out between the air silencer box and cover as you could see the oil dripping from the seam between the two.
 

OldOMC31

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Use aviation permatex to hold the gasket in place then torque it correctly. The oil was always in there you just never saw it. ALL carbs leak when you tip the motor up.
Would it be wise to check the cover for flatness/sand it down the same way you would a head (figure 8 pattern on a flat surface with sandpaper). Will definitely try the Permatex next time I'm there. Do you happen to know the proper torque for these 3x bolts?
 

flyingscott

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Buy the best gasket you can OEM if possible. The thinner cork used today does have more of a tendency to leak
 

OldOMC31

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Buy the best gasket you can OEM if possible. The thinner cork used today does have more of a tendency to leak
The new gasket I picked up was cork OEM. Now that I used it dry and bottom got exposed to oil, will the aviation permatex work still or do I need to get a new dry cork one again before trying the permatex?
 
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