Corroded spark plug on DF50

KjetilBN · #1 (**permalink**) 10-02-2011, 11:33 AM

Yesterday when doing maintenance before the winter, I discovered that the spark plug for the lower cylinder was slightly different than the two for the upper cylinders. The plug for the lower cylinder was a bit corroded (rust) on the part of the threads that is inside the cylinder. The electrode and insulator looked the same as the two others.
Normally the engine is not emitting any smoke, but when I saw this I remember one time this summer that I noticed a bit white smoke when I came back to the dock after a trip and the engine was idling.
Is this something I have to be worried about?
I bought the boat and engine this spring and starts to be afraid that I have done something stupid.
The engine is a 2001 year model and have done about 260 hours.

kmoose · #2 (**permalink**) 10-03-2011, 08:44 AM

the corroded plug in the bottom cylinder sounds suspicious and I would at least have someone check it out. How is the oil........ clean, milky? I wouldn't go jumping of a bridge over it as it is nearly 11 years old and may require some work. Have it checked out at a service center and see where you are at.

KjetilBN · #3 (**permalink**) 10-03-2011, 03:41 PM

The oil is clean,not milky. The oil level has not changed this season.
I find it strange that there normally is no smoke from the engine, only noticed a bit of white smoke a couple of times this summer.
Will a compression test tell me something? I have a simple compression tester available. Is it straight forward to do this on this type on engine? I have never done it on a 4 stroke EFI.

redlowrey · #4 (**permalink**) 10-04-2011, 06:45 AM

Keep an eye on it, are you sure it is smoke and not steam if is water getting in it will start missing when enough gets in. About two threads of the spark plug protude into the combustion chamber and when water gets in it usually starts rusting and corroding the bottom of the plug.

kmoose · #5 (**permalink**) 10-04-2011, 09:34 AM

Quote:

Originally Posted by KjetilBN

The oil is clean,not milky. The oil level has not changed this season.
I find it strange that there normally is no smoke from the engine, only noticed a bit of white smoke a couple of times this summer.
Will a compression test tell me something? I have a simple compression tester available. Is it straight forward to do this on this type on engine? I have never done it on a 4 stroke EFI.

Compression check is is the same, just pull all the spark plugs and spin it till the gauge stops moving up.

I'm with redlowery, keep an eye on it and if performance changes you'll know something is up. There is a chance that the exaust valves were in an open cycle on that cylinder when you last used it before pulling the plugs.