Has anyone got any ideas what might cause excessive crankcase pressure? A guy I ride with is having troubles with his oil tank dipstick blowing out. He has an 08 Heritage. I've looked it over and can find nothing wrong. The bike runs good, compression is good (no blow by) and the bike is not over filled with oil. He's even replaced the dipstick, thinking that the fit had gotten loose over time. Along with this it seems to be making his rocker box seals to start to wreap, but that may not be related..

 

Excess crankcase pressure is typically caused by a less than optimal ring seal.

With the oil cap or breather hose off, put your hand over the opening, and rev the engine a bit. If you can feel a good amount of air coming out, chances are the motor needs some help. Then move on to other diagnostic tools, such as doing a leak-down or compression check.

 

I already did the compression/leak down test and there appears to be no problems. I haven't done the part with the oil cap off, but I will. Is there any kind of a crankcase breather that I'm not aware of?

 

There is the breather vents in the top of the heads.

 

maybe the dipstick is loose



Bob
1997 Heritage

 

Had this happen when umbrella valves were installed upside down by mistake. But it can also happen if the umbrella valves are going bad.

 

What do you mean by umbrella valve? That's a new one to me. Since there's no blow by on the rings I am kind of suspecting the crankcase vent not working properly and that's why I asked about it. But he'll, I don't even know how to find them..

 

The umbrella seals are in the rocker box and prevent excess oil from blowing out the vent tubes that connect to the air cleaner. Even if those were bad, it wouldn't cause the dipstick to blow out.

Maybe if the head vents were blocked completely by someone who installed solid bolts rather than the hollow ones, that might cause the dip stick to blow out. That would mean no where else for the excess pressure to go.

 

Umbrella valves and/or the two vents on the rocker boxes that usually discharge to the throat of the throttle body, is what came to mind when I read the title.

Also, don't fill it above the 75% mark.

 

Where on the rocker boxes are the vents? I'll check them out if I know where to look..