Mercury 50 hp 2 stroke white Milky spark plug...help please!

geojay

Cadet
Joined
Jul 24, 2011
Messages
9
Hi
I have a 1970 Mercury thunderbolt ignition 50 hp 4 cylinder 2 stroke outboard which has been running fine untill last week when it lost power, I removed the spark plugs and found that the bottom one has a white Milky substance on, once replaced It runs fine for about 30 mins then creams up again.
Has anyone had this before and where is it most likely leaking water from?, I removed the top plate and replaced the gasket but hasnt made it any better.
Thanks for any help in advance.
Geo
 

HAS

Petty Officer 2nd Class
Joined
Jul 16, 2010
Messages
140
Re: Mercury 50 hp 2 stroke white Milky spark plug...help please!

geojay
i think the lower crankshaft seals are bad. the more you run this engine the more damage is
done to the piston the cylinder wall and crank. the powerhead must be removed and the lower
seal/bearing end cap. when the end cap is removed you will be able to see a little of
the piston the cylinder wall and connecting rod, check the crank end of the rod for more
then normal play. i'm not an outboard mechanic but this what i found when i got my 1985
50hp. 4cyl. 2 years ago, compression was down 40psi. on the lower cylinder, i replaced the seals
but the damage was already done, now i'm looking at an overhaul this winter.
there are mercury esperts on this forum and they and they can help you more then i can. ....good luck.....HAS
 

geojay

Cadet
Joined
Jul 24, 2011
Messages
9
Re: Mercury 50 hp 2 stroke white Milky spark plug...help please!

Thanks for your input, I was thinking this may be the case as someone else had a simular issue that I read yesterday and it always effects the bottom cylinder, When I removed the water jacket cover all apart from 2 of the bolts snaped and needed to be drilled out so I was hoping that I didnt have to tamper with it too much, Im going to remove the engine this weekend and strip it - I think as its age most parts are discontinued so hopefully not too much breaks, Was it quite apparent where the water was leaking from when you removed the power head?.
Thanks.
 

HAS

Petty Officer 2nd Class
Joined
Jul 16, 2010
Messages
140
Re: Mercury 50 hp 2 stroke white Milky spark plug...help please!

geojay I don't remember if there was any sign that the seals were bad. I talked to
the people at the Mercury dealer about the low compression, at that time on a 24 year old
engine, cylinders 1-2-3 comp.135 TO 140, no.4 comp.100, they told me to replace the lower
crankshaft seals. Thats how I found out about it. When I took off the seal/bearing end cap
I could see the scrapes on the part of the piston and cylinder wall that I could see. I knew
then that it was only going to get worse, now no.4 is down to 80p.......GOOD LUCK WITH YOURS
..........HAS
 
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