cylinder head leaking water

[markdavid]

I have a "78 40 hp that I just bought used. Running it now I see water coming from below the top spark plug. There is a fine hairline crack at that point. Is this crack weldable or do I need a new head? <br />Thanks,<br />Mark

 

[WillyBWright]

Re: cylinder head leaking water

That's not really a head. It's just a water jacket cover. You can probably just clean it off real good down to the metal and JB Weld it. Make sure the water pump is working okay. Leaks around the sparkplug are uaually caused by warpage from overheating. If the motor survives the ordeal otherwise, replacing the gasket is usually enough, as well as rebuilding the water pump. It's possible that the crack is just a casting mark, but if you're sure it's a crack, try the JB Weld thing.

 

[andrewkafp]

Re: cylinder head leaking water

Do a search on "Water leaking from spark plugs"<br />It's a common early Merc thing and Willy is correct. It is caused by corrosion and can be fixed with JB. If you need to remove the cover, you likely snap bolts and will need to rtemove the powerhead and re-drill and tap new threads.

 

[markdavid]

Re: cylinder head leaking water

If I fix the hole with JB weld and there is no visible leak how can I tell if the gasket needs replaced? It seems that Unicorn is hinting that it is a frustrating job. Is there a possibility that water is leaking into the cumbustion chamber?<br /><br />Thanks,<br />Mark

 

[andrewkafp]

Re: cylinder head leaking water

Iboats member Clams Canino stated that it is very unlikely that it will affect the combustion chambers. You can tell by checking the plugs. If one is very clean, and the motor has a miss,you will know.

Water coming out around the water jacket cover around the plug holes is common. That thing is not a cylinder head - it's a cover. That cover is bolted around the perimiter and often leaks around the unsupported plug area holes. Taking off those bolts usually results in breakage. If at all possible clean the area well and use silicone seal to re-seal it. As long as those leaks arent severe, they are relativvely harmless. The system is very low pressure.<br /><br />As for the rest - how lucky do you feel? In the case of a crappy water-pump #1 will fail first, as it's the highest. If you're lucky you can replace #1 (possibly getting it bored .015 over) and re-ring the other 5. It's cost prohibitive to go .015 over on all 6, so if the other 5 are well worn, you'll have to live with it. If it ran good before the problem - it'll prolly run just as good after you fix the problems.<br /><br />-W<br />