Oil on spark plug threads, Rotax 4 Tec

[Tommy Lee]

So... I know that this is somewhat of a tackled subject, both here and on other web sites dealing with both automotive and marine engines. I am just wondering however, if in my case I am dealing with simply a failing valve cover gasket, or worst case a possible leaky piston chamber (I freaking hope not), or other issue that could cause this.

When I changed the oil and filter last week, as well as spark plugs before my first launch of 2021, I noticed the oil was about 1/3rd to half less than it should be, and that's when I noticed the oil on the spark plug threads. The engine/boat only has 111 hours on it. The engine did not misfire at all when driving it for the couple hours we took it out last Saturday.

My question at this point is, considering the number of hours, the amount of oil missing etc., is this probably more serious than a valve cover gasket issue? Should I try tightening the valve cover (check by tightening to torque spec and see if the bolts are not torqued all the way) before ordering a new gasket? If it is the valve cover I would imagine there'd be oil pouring down the sides of the engine or pulling somewhere other than inside the spark plug wells?

Thoughts?

 

[RobbieO]

Sometimes oil collects in the spark plug cavities when the gaskets are leaking, and as you are removing the plugs, it drains onto the plug and the threads. I have seen this in automotive applications. Next time, have a look in the cavity before you pull the plugs. If you had oil in the chamber, the plugs would be fouled like a 2-stoke. You have a Scarab, so I have no idea how those engines are setup. This may not apply.

 

[Tommy Lee]

Sometimes oil collects in the spark plug cavities when the gaskets are leaking, and as you are removing the plugs, it drains onto the plug and the threads. I have seen this in automotive applications. Next time, have a look in the cavity before you pull the plugs. If you had oil in the chamber, the plugs would be fouled like a 2-stoke. You have a Scarab, so I have no idea how those engines are setup. This may not apply.

That's what I am figuring. My concern however is the amount of oil I believe is missing after suctioning out the old oil during the change. One would figure based on that, that the pooling in the spark plug wells would be obvious and somewhat excessive. Thoughts?

 

[josh195]

Did you get the full amount of oil out during the oil change? I haven't done it yet myself but I believe you need to suck oil out then crank the engine and repeat to get the proper amount of oil out.

 

[RobbieO]

That's what I am figuring. My concern however is the amount of oil I believe is missing after suctioning out the old oil during the change. One would figure based on that, that the pooling in the spark plug wells would be obvious and somewhat excessive. Thoughts?

Depends on what the oil level was before you started. I wouldn't be concerned on how much oil you extract, as long as you put back what you took out and end up with the same oil level. I know on Yamaha's, you usually can't extract all the oil. I read somewhere that suggested pulling the oil hose off the cooler and extract more oil from there. That's what I will try.

 

[Tommy Lee]

Did you get the full amount of oil out during the oil change? I haven't done it yet myself but I believe you need to suck oil out then crank the engine and repeat to get the proper amount of oil out.

Yes I believe so, but I did not crank after the first pull. However, my first oil change yielded at least three quarts without cranking the engine, and that was the full amount expected for this engine. I am probably going to jump in there after work tonight to see if any oil is pooling in the plug wells or down the sides of the engine.

 

[Winerocks]

As others have said, the missing oil is likely not anything to worry about. I forget the volume that can be retrieved by cranking, but it is significant,,,a quart or so. It takes a decent amount of cranking to move the oil to the sump area where you suck it out, There are o-rings that seal the valve cover around the spark plug tubes. These harden over time, and eventually crack, leak, and allow oil to pool around the plugs. Lots of info on Seadoo forums about this.