Merc 850 problem

[AZCoyote]

Hi everyone, I just found this forum researching a problem I'm having with my 850.<br /><br />I have an early 70's 850 that I keep in great shape. This engine looks new and I change the gear oil every year and the impeller every two. Due to getting married and buying a new house, my boat has sat covered for two years. This moring, I put fresh gas in it and tried to start it. It fired up in about 20 seconds. I had taken the cowl off the motor figuring it would be hard to start. While I let it sit there and run, I noticed water seeping out around the top sparkplug.<br /><br />The engine runs great, idles fine, and does not smoke. The water that leaks out is clear and clean. <br /><br />How big of a problem is this? I have to assume that a gasket somewhere has failed. In AZ, Marine shops won't work on an outboard this old so I would probably have to do the work myself. I am very mechanically inclined, but I have now idea where this leak would start.<br /><br />Can someone help me narrow down what causes this and how much trouble the repair would be?<br /><br />Thanks!

 

[andrewkafp]

Re: Merc 850 problem

It's most likely coming from the water cover (Not head) and can be fixed with JB weld. This fixed my 1980 50, but for a proper job, you will need to remove the cover and you will most likely snap bolts. This means P/H removal. The water will not enter the combustion chambers from THAT leak, but if there is a lot of corrosion there, another leak might start elswhere. My bet.. Can't go wrong with the JB.

 

[Clams Canino]

Re: Merc 850 problem

Yep.<br /><br />Pressure there is only about 8psi. Dry it well, and goop it from the outside.<br /><br />-W

 

[AZCoyote]

Re: Merc 850 problem

Thanks for the help.<br /><br />Just so I'm clear, are you saying to just seal the leak from around the plug? And that's ok? Is there any long term danger with that fix? I just don't want water to find it's way into the combustion chamber.<br /><br />Thanks!

 

[Clams Canino]

Re: Merc 850 problem

It can't from there. That is not a cylinder head, it's just a water jacket cover. The heads on those are cast into the block, non-removable.<br /><br />All that can do is leak to the outside of the motor.<br /><br />Remove the plug, clean and dry the area *well*, and then goop the circle where the cover meets the plug boss. Replace the plug before everything hardens in case of overage.<br /><br />The "correct" way to fix it is to remove the powerhead, remove that cover, deal with all the broken bolts resulting from removing that cover, and putting a new gasket (with goop) under that cover. I would never - ever - do that unless the thing was coming apart anyway for internal engine work. Note that when I do a rebuild on an inline I *still* don't pull that cover, unless there's a sign of a leak.<br /><br />Fixing them from the outside is the SOP.<br /><br />-W<br /><br /><br />-W

 

[AZCoyote]

Re: Merc 850 problem

Well that makes me feel better. Thanks!<br /><br />One last question though... It almost sounds like the procedure you guys have described with the JB weld will secure my sparkplug in place. Is that right or am I missing something. I would like to be able to change my plugs someday! All I'm really doing is making a gasket/seal for the sparkplug threads. Right? Thanks!

 

[Clams Canino]

Re: Merc 850 problem

NO<br /><br />The leak is where the cover meets the spark plug boss. Remove the plug and clean the area carefully and you will see the leaky seam. The sparkplug and threads are NOT the target. Your target is a circle 1/8 inch away from the plug hole.<br /><br />Picture that the thing the plug sceres into is really a 1.5 inch diameter, flat, metal boss. And that this cover meets it all around the plug.<br /><br />Got it now?<br /><br />-W

 

[phatmanmike]

Re: Merc 850 problem

why does everybody talk trash about mercury bolts braking and not to remove that cylinder head cover. ive removed mine NUMEROUS times with no problems at all! <br /><br />or is my merc 1150 special

 

[AZCoyote]

Re: Merc 850 problem

Yup, got it. Thanks!

 

[Chris1956]

Re: Merc 850 problem

Mike, In my experience, fresh water motors come apart without many (or any) bolts breaking. If you are going to use them (but not keep them) in salt water and flush them each trip, tha same rule applies. If you keep them in salt water or don't flush them after salt water usage, they corrode up!. I have used permetex #2 on bolt threads to keep them from rusting into the motor, with good success. I am starting to use antiseize (graphite-based??) compound instead.

 

[Clams Canino]

Re: Merc 850 problem

The more you remove it, the more easy it is to remove. Try taking one off that hasn't been removed for 30 years. Even the fresh water ones can be problematic. You're lucky is all. Except that you should not have to remove that cover but once perhaps in your life - why so much?<br /><br />-W<br /><br />

Originally posted by phatmanmike:<br /> why does everybody talk trash about mercury bolts braking and not to remove that cylinder head cover. ive removed mine NUMEROUS times with no problems at all! <br /><br />or is my merc 1150 special

 

[andrewkafp]

Re: Merc 850 problem

You can use another type of putty called <br /> http://www.afcinternational.com.au/site/data/16002_tech.htm <br />Same principal applies, but the the trick I used is to add some lubricant to the plug washer and thread and tighten it on the soft putty. When the "Goop" (The man is back).. sets, you remove the plug and the washer should come out or be able to be popped out with a screwdriver.<br />As far as the bolt breakage., There are very small diameter, and any resitance can snap them if not removed for a few decades.<br />As I said.. the goop has worked on my 1980 50 so far..

 

[AZCoyote]

Re: Merc 850 problem

Well, I "gooped" it up tonight. I'll fire it up tommorow night and see what happens.

 

[Clams Canino]

Re: Merc 850 problem

If it still weeps a little don't panic. The lower cowling ("belly pan") has drain holes in it. <br /><br />-W

 

[andrewkafp]

Re: Merc 850 problem

Trick no 2.. If you run it in salt, and there are still a few drips, remove the plugs and mask up the thread and electrode. Spray a VERY THIN coat of auto clear on the metal end. This will stop them rusting and won't affect the heat range. I do this and have found no problems. Or you can just use WD40.

 

[AZCoyote]

Re: Merc 850 problem

Well, that fixed the leak. Thanks!

 

[andrewkafp]

Re: Merc 850 problem

You know it's gotta be good stuff when our own Ancient Mariner goes by it's name.

 

[Clams Canino]

Re: Merc 850 problem

And another thread heads off into final obscurity... good deal.<br /><br />-W