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bf 75 engine oil ingression

R

rogsnow

New member
I'm looking for the main gasket or part failure that causes water ingresson in the engine oil of a bf 75, the engine oil level rose and overflowed after trimming up after a short running time on its mooring.The oil had become an emulsion consistency.
 
The link below illustrates the cylinder head gasket (item 4) and the block to oil case gasket (item 2). If you look carefully at the block to oil case gasket you will notice that there are perimeter holes for the case to block bolts to feed through.

In addition, there is a larger hole in the gasket. In this depiction it is at the "north" portion of the illustration. That hole is to allow the water pump stream flowing from the pump up through the oil case to enter the engine block. There is an O ring that is depicted on another page (provided further below) that sits in a depression in the oil case and is surrounded by that hole in the gasket. That is the most direct route for water to enter the engine oil. Item 21 illustrates another O ring that would be suspect at the cylinder head gasket.

Those are the two places to look but, as you can see, would require some major surgery. If that is what you have going on, it would be fortunate because otherwise, the head or the block has failed due to corrosion and they are no longer serviced.

http://www.boats.net/parts/search/H...04/CYLINDER BARREL + CYLINDER HEAD/parts.html

Below is the link to the page that depicts the oil case to block water passage O ring. It is item 31

http://www.boats.net/parts/search/H...75-1013304/OIL CASE + ENGINE COVER/parts.html

Hope you can get her fixed. If not, there are plenty of guys like me that will buy one for parts.
 
If the BF75 is the two cylinder that Jimmy is showing, there is one other place that can also be an issue. The o ring seal of the oil fill. See part #14. http://www.boats.net/parts/search/Honda/Outboard%20Engine/0/BF75%20LA%20VIN%23%20BF75-1000002%20TO%20BF75-1013304/OIL%20PUMP%20%2B%20OIL%20FILTER%20%2B%20MUFFLER/parts.html
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See the bottom right corner of the seal where there is an "o"? As crazy as it sounds, there is a water passage through that little o. Many of the oil fills were plastic and sometimes warp. That causes the water (under pressure) to go right into the oil. It is possible for the seal to fail over time also. If the fill is plastic, I would replace it with the newer metal one.

The trouble is, you can not get it off without pulling the power head. You can not get the bolts out far enough because of the case. Some folks have drilled a couple of holes through the side of the case to allow the bolts to come through. You can always plug them back up with plastic panel plugs.

Mike
 
Nice catch Mike! I did not know that. I've never taken one of those off but I can see the hole in the gasket for the o ring just like the one in the oil case to block gasket. I'm still a rookie.
 
My BF75 just started doing the same thing, started sounding strange, started slowing down and speeding up on its own, we were 3 miles out in the ocean so had to keep it running. Checked the oil it was like coffee, changed oil 3 times, ran in a bucket and water kept getting in. Check the plugs and the top plug had some corrosion. Guessing head gasket cracked water was getting in top cylinder and cutting in and out, sound right? Will let you guys know when we take it apart tonight.
Guess you can't run these things at full throttle for more than a couple of minutes?
 
coffeeoil,
Yes, please let us know what your findings are. As far as not being able to work these engines wide open for a long run, I would have to disagree. Many of these engines that are still in service are 20 to 30 years old. Many are second hand, third hand and beyond purchases and are still providing their latest owners reliable, dependable operation. All the while, they may have received questionable or no maintenance other than to "fix what broke" during many of these years and owners.

I saw my first BF 100 (pretty much the same engine, different cam) in 1979 when I drove up the coast to help my buddy bring his new, to him, sailboat to San Diego. I was amazed at the quiet, easy starting four stroke Honda that was on that boat. Up until then, I had only used 2 stroke outboards and to have something that ran so smoothly and quietly with no smoking was a real pleasure. We ran that engine wide open all day that day. Of course, it was pretty new at the time. I wanted one after that but when I saw how much it cost, I stuck with my old 12 pull minimum Chrysler smoker. My friend still has that boat and that Honda and I saw it run full throttle for about 2 hours last summer when the wind completely died and we needed to get back to the mooring.

Those babies are tough and that's why there are still so many around. Good luck with your repair.
 
Thanks for the input jgmo,

Turns out the upper water resevour of the head gasket had basically melted into a large circle. Good to know these things can take a beating, looking to upgrade to a 90's 15hp honda four stroke. Wish I knew why it melted, never smoked or anything, runs cool to the touch, prevois owner said he just rebuilt it. Lots of screws have been wiggling loose during operation, wonder if he know what he was doing. Should we use some locktight on the screws? Or did he just not torque them enough you think?
 
Well, they can take the running but they can't survive a hack mechanic...nothing can.

When you say screws were backing out, did you mean the head bolts? If so, there's your answer as to what failed the head gasket.

I wouldn't use Lock-Tite on head bolts. It actually alters (increases) the torque that needs to be applied to put the bolts in proper tension where they will stay permanently.

If the guy didn't use a torque wrench, he may have OVER tightened the bolts and elongated them. That will make them loosen up eventually. You should look at them carefully before choosing to reuse them. If any of them have a "waist" (smaller diameter in the middle of the threaded portion) get rid of them.

Also, If he tightened the head from the outside in, he could have "bowed" the head in place and that could have failed the gasket. Here is where a good straight edge can tell you if it is permanently warped or not. If you don't have a strait edge, just lay a large, flat, fine toothed file across the head and see if there is a lot of daylight between the file and the gasket surfaces. Do the same on the block.

Keep us updated.
 
Replaced the gasket put it all back together and torqued correctly, and it runs better than it ever , no more coffee oil. Thanks for all your help. Just wonder why it happened, previous owner said he rebuilt it but the head gasket looked old. Runs cool to the touch dont know how it melted.
 
Glad to hear you had success. As far as the old looking gasket, one man's rebuild is another man's tune-up and oild change. Who knows what he did and called it "rebuilt"?
I hope she runs a long time for you.
 
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