Merc 500 - water coming out of spark plugs

[krypton]

Hi, <br /><br />I have and older Merc 500 50hp outboard (around 69-71 model) and it's dribbling out water around the base of at least two of the spark plugs. Is this bad news ? <br /><br />What is the likely cause of this and what is involved in repairing it ?<br /><br />Thanks in advance.

 

[krypton]

Re: Merc 500 - water coming out of spark plugs

I was thinking of removing the head cover plate to have a look and see if the water gasket maybe damaged. If I remove the head cover to have a look do I have to replace the gasket underneath or can I just fasten it right back up again without having to replace or re-seal anything ?

 

[Troy_from _Oz]

Re: Merc 500 - water coming out of spark plugs

hi there Krypton,<br /><br /> I had a similar problem with my merc 650. I had a really close look at it and determined that there was corrosion on the head? between the the head and the water cover gasket near to one of the spark plugs. This had slowly eaten away the head and water gasket. Unfortunately it looked like quite a major repair requiring refacing (and possibly welding) of the head before a new water jacket gasket could be fitted = $$$ (anythingon my 1971 650 is expensive to fix/replace). These repairs would have cost more than the motor is worth, so i decided to use liquid steel to fix the problem. I know many are choking about now, but i do have a very good auxillary and only use the boat for inshore fishing. Indeed - i normally dont condone dodgey jobs like the one ive done, so just take it with a grain of salt.<br /><br />I guess the moral is that it might be more than just a gasket that has failed. In my case, a new gasket wouldnt have solved the problem - and im guessing a liquid-type gasket sealer would have failed also. <br /><br />Anyway -the repair has been been holding up well.<br /><br />don't know what things will be like in NZ in regard to outboard repairs etc but i expect they are similar to over here in OZ with parts/mechanics etc.<br /><br />Best of luck.<br /><br />Troy

 

[Chinewalker]

Re: Merc 500 - water coming out of spark plugs

Hi Krypton,<br /> Not an uncommon problem on older Mercs. You'll have to pull the cover plate off - don't worry, nothing's going to jump out at you. Be prepared to break some bolts. <br /> If what's underneath is corroded somewhat, you can fill the pits with Marine Tex or JB Weld, then sand flat. If possible, save the old gasket as best you can to use as a pattern to cut a new gasket. If you've got a long-established Merc dealer in your area you may get lucky and find a new gasket in stock, but you're probably going to have to get some gasket material and cut one. Lightly coat both sides of the gasket with PermaTex Form-A-Gasket, particularly around where it was leaking...<br />- Scott

 

[tmac58star]

Re: Merc 500 - water coming out of spark plugs

Good advice from all so far. I would add that you should soak the cover bolts/nuts in PB Blaster or WD40 for a day or so, then run the motor to get it up to temp before pulling the cover. Makes getting the bolts/nuts off easier if the engine is warm. On an engine that old, you will twist many off if done cold.

 

[Dershman]

Re: Merc 500 - water coming out of spark plugs

I played this game already this summer with my 1980 merc 40. My peehole cloggeed and the easiest route became the upper plug hole. I warmed the engine, liberally applied and reapplied pb blaster - You will break bolts; hopefully they will be the upper bolts that you have easy access to drillout and retap. Many of my bolts were the consistency of chalk - removing them was the hardest, most time consuming part of the whole ordeal. I drilled and tried "easy outs", they broke off ( and then I had hardened steel cores in the broken bolts -arrgh). I ended up drilling out the entire bolt and retapping. In one case I needed to over drillthe hole to get around the hardened steel, tap the hole for an oversized bolt, insert the bolt and drillit out -to get back to the proper sized hole then tap that to the proper size. <br />the gasket replacement was a breeze, I was able to get the exact part from my merc dealer, $4. I had a buddy plane both the head and the cover before reassembly and re-installed it using gasket seal - figuring I would never again have to open it. It still dribled a little so I tightened the plug and was back on the water.<br /> <br />If I had to do it again on an engine this old I think I would try mickey mousing it first with goo around the plug hole. It took a long time - thankfully I didn't have to pay myslef for my time.

 

[NEECAPRS]

Re: Merc 500 - water coming out of spark plugs

Old Mercs: Haven't seen this mentioned yet. On my 1965 100hp I had this leakage trouble. I didn't take the time to replane the parts. Instead used extra 0.020" gasket for sparkplug holes only to put more pressure in that area. With lots of hardening Permatex it worked well. Made sure the gasket stock was soft by humidifying then tightened everything slowly.

 

[catmania]

Re: Merc 500 - water coming out of spark plugs

Okay same problem with my big old merc, I figure I will have the same problem with bolts breaking etc. Its just a tiny amount of water dribbling out say a drip every couple of minutes from the top few plugs on a inline 6. Would you think that just leaving it as is is an option or is this something that should definitly get fixed?<br />I figure i can do it myself... but i know what horror drilling and retapping bolts can be and i would rather not go there. Is there something i could do externally to solve the problem?

 

[krypton]

Re: Merc 500 - water coming out of spark plugs

Yeah, if it's only a small amount of water coming out, would it do any harm to leave it for now ? We only really want to get a few more months out of the motor and then we are going to upgrade.<br /><br />I have noticed a smallish hole in the thread of the top spark plug caused by corrosion of the salt i guess (lots of salt buildup around that plug from the water seeping out). How could I patch up that hole, would some kind of silicon do the job ?<br /><br />Thanks for all the great advice so far !

 

[Troy_from _Oz]

Re: Merc 500 - water coming out of spark plugs

Catmania/Krypton <br />Mine started out with the same problem - one drip every few seconds. I just left if and went out boating another two times. This all happened as a result of the last owner not replacing the impeller - hence not enough water was making it up to the top of the motor when flushing i think. When i replaced impeller -more water+extra pressure. Anyway - back to the story. After two more boating sessions plus the increased water pressure, my pinhole leak turned into a hole about 4-5mm across. the semi-corroded parts of the powerhead were also flushed out with the increased pressure = bigger problem. hmmmm -procrastination cost me again!<br /><br />As per my previous post, I used quiksteel which is a steel-based? two part epoxy to plug up the hole. I didnt want to go through the drama of drill/tapping/breaking bolts on an engine worth about US$100. It seems to be holding up with no problems so far. As i said earlier though - its not the absolute best way to do it - but then id half like to upgrade the motor at some stage also.<br /><br />Krypton - apparently you can drill and tap this quiksteel stuff - maybe thats an option for your spark plug thread??? not sure on that one though.<br /><br />Best of luck - Troy

 

[y2j]

Re: Merc 500 - water coming out of spark plugs

you guys are in luck.. I just completed this job on my 650cc Thunderbolt <br /><br />EVERY BOLT SNAPPED EXCEPT 1 <br /><br />Drilling them out took all day but guess what.. In these older mercs its a nut and bolt combo not a threaded hole so you can drill em out yourself <br /><br />When i took it off shock horror! Foamy white crap everywhere (corrosion) And salt water had eaten away around the spark plug.. In these circumstances only a cold weld is the option and then sand it down and use instant gasket type stuff liberally around on both sides of the gasket especially where there are holes.<br /><br />When you open it all up it would be wise if you clean it all up (take off all the corrosion around the jackets) And do the above of using a cold weld filler such as a 2 part steel hard filler that withstands heat and seal it all up<br /><br />Then flush after every trip even if its freshish water. Then it will outlive you <br /><br />In my scenario i had to buy a new water jacket cover.. New side pod cover and new exaust cover.. all of them had holes which made water spray into my motor also $200 US dollars later i have a fresh new motor for another 20 years

 

[andrewkafp]

Re: Merc 500 - water coming out of spark plugs

But how do you re-drill the bottom bolts, when there is not even enough room to get your hand in there to remove a spark plug ? Let alone lining up a drill. Do you need to 1. Remove the powerhead or 2. Drill some hole through the bottom cowling and re-fill them later ???

 

[y2j]

Re: Merc 500 - water coming out of spark plugs

mate you take out the whole block from the actual shaft.. like take the whole thing into your house and sit it on the flywheel and remove them <br /><br />U have to only unplug 2 wires, take off the support brakets (2 of them) and undo 8 nuts then get 2 of your mates to pry it off with you

 

[y2j]

Re: Merc 500 - water coming out of spark plugs

Oh btw u have to remove the block anyway to retrieve 1 or 2 of the nuts if i remember correct <br /><br />BTW you will have to buy alot of drill bits or know how to sharpen them to do it also. And get a good nail punch

 

[andrewkafp]

Re: Merc 500 - water coming out of spark plugs

OK