I have a '97 FLHT and recently had the engine rebuilt after a cam gear broke and spun everything out of whack. I did replace the original cam with a slightly bigger one just to open the valves a little more. I thinkI went from an Andrews EV20 to EV24. Wiesco pistons, new valves, push rods etc. After the rebuild I have noticed that if I am running 75/80 mph (3300/3500 rpm) for a distance my oil fill cap will blow off and of course oil flies out all over the place. Once I get home let it cool and check the oil it is over full, way over full. Is it creating enough of a negative vacuum in the crank case to cyphon oil from the primary to increase the volume of oil in the crank case to then have this happen? Is there something I can do (if that is the problem) to better vent the crank case? Or any suggestions as to what is going on? This doesn't happen evertime but enough that it gets frustrating. Thanks in advance as I've almost exhausted all means of a remedy.

 

How much oil is in the primary? Usually, it goes the other way when that seal is bad, that is, from the motor to the primary, which becomes overfull.

Is the breather timed correctly?

That bike has umbrella valves. I'm not sure what a failure in those would do for you, but I think it would mostly blow oil out the breather, not over pressure the oil tank.

Are the oil lines hooked up properly? Go through the lines in the book and compare.

 

Most likely cause is it is over full of oil to start with...that will blow the cap. Have you checked the primary? If you are checking the oil cold and adding oil....you could have oil in the crankcase due to a leaking checkball in the oil pump...and when you crank it, the oil in the sump goes into the tank causing an overfull condition...if you check the oil and it is low...crank the bike, and check it again after it has run for a while.

 

Dr. Hess: I put one quart of 20/50 amsoil in the primary. I use the same in the crank case. I can only assume that seal is ok as this only seems to happen at those high rpm's for an extended period of time. While cruising around back roads I've never had the issue. I check the oil a lot. There is a cold and hot mark. In one example I check it cold and it is on the correct mark, go for a ride and am on the interstate cruising in the 3300/3500 rpm range for several miles and a good chance it pops. I get home get it all cleaned up let it cool, check the oil and it is way over full. I then cyphon oil out and the last time I took about a half court out. It was originally filled with 3.5 qts of the 20/50 amsoil. I know oil expands when hot but not that much. I then check the primary and its hard to tell if it went down, would have to drain it to be sure. I've only changed my own primary oil one time so I don't have the trained eye to remember where that level was at that time. I know right now it is touching the starter gear on the clutch while straight up and down on the jack. I took the breather hoses off each head and made sure they were not blocked and they were good. Further than that I don't know. I've been told and read about having too much oil will do that and yes that seems to be the case but why it is getting overfull, is it possible to be sucked out of the primary in those high rev conditions? I guess it has to come from somewhere. So do I need to have the breathers in the heads drilled out more, not sure about umbrella valves, sounds like more than I can deal with there. I do appreciate the return information. Just my luck to have something strange that you just can't put your finger on.

Tom84FXST: I have never had to add oil. I have no leaks and most times it is where it needs to be, it's like I mentioned to Dr. Hess it only checks overfull after I have an incident where the fill cap blows off. and by the way what a mess, pipes are hard to get clean after oil has baked on.

In a way things do come together somewhat. Last summer I had the bike safety checked before riding to OC, MD for bike week. I had them change the primary oil. the next time I decided to learn to do that myself which now I know is very easy, but when I went to drain the primary there was not much oil in there, I mean ounces, no where close to even a half court. So that leads me to think the oil is being sucked out into the crankcase somehow. I'm not sure if that means the seal is going bad or if the laws of physics take over and it goes the path of forced resistence if you will. I was hoping someone on here would have maybe experienced a similar thing. Again thanks so far for the information.

 

I had my bottom end rebuilt some years ago, and after that I had oil getting sucked into the crank from the primary, primary would go dry, and the oil would blow out my breather and leave huge puddles. The guy that rebuilt the bottom just shrugged his shoulders. After 3 years of that crap, I got talking to another local indie. He said he had seen it one other time, and he told me the story. Anyway, I took it to him. The seal was good, it was the spacer. I expect the rebuild guy used the old spacer, why would it be bad? So he replaced my seal AND the spacer, and he ran a bead of loctite around the inside shoulder. Problem solved. That's what he did with that other bike, and it fixed that one too. Now my primary oil stays in the primary, except for the leaks, and my crank case oil stays in the crank case, except for the leaks. That's my story.

 

The extra oil has to come from somewhere. Blueharley has a suggestion which seems reasonable to me.

I would keep a very close eye on the primary oil. If it is sucking in from there, that's your problem. You might consider adding a UV dye to the primary oil, going for a ride, then checking for UV dye in the engine oil.

 

First: Get a FSM (factory service manual).
Second: Drain all the fluids, replace the oil filter, and refill to factory specs (my primary takes 42 ounces - more than one quart-when fully drained)
Check the routing of the oil lines. Just to be sure.

Ride the bike again and see if it blows the dipstick out of the pan. If it does, check your fluid levels. If one is up/down you know you've got a seal leaking between the engine and primary. If not, you're going to need to start looking at the breather timing and the umbrella valves (yes they do get installed in the wrong holes).

At that speed/rpm, a bunch of oil is in the upper part of the engine (rocker boxes). Usually, you blow one of the seals on the covers, but it sounds like the dip stick is the 'safety valve'.

The FSM has an excellent section on the oiling system of the EVO. Study it, and you should be able to diagnose most issues.

Otherwise, take it back to whomever worked on it last...

 

Very good, thank you all for sharing. Once I pinpoint it I will reply with what we found. I'd almost bet is has something to do with the seal.

 

I just stumbled upon some information and wanted an experts thoughts...

While picking up a new oil filter and primary gaskets to service my bike the parts guy said I had the wrong filter for my year of bike. the K&N I picked up was for the twin cam engines due to the small oil passages they have more filtering so to be absolutely sure no dirt clogs them up. He said for my evo it requires higher oil flow and that could lend too much oil to be left in the crankcase causing internal pressure issues. I have been using this same oil filter since my engine was rebuilt and also when the oil plug popping problem began.

Could that possibly be something that is causing too much oil to get into the oil tank at one time and eventually blowing the cap? Knowing it only happens at higher rpms it would make some sense when things are trying to move fast and are being held up by the filter. My luck isn't that good so I doubt it will be a $17.00 fix....thoughts?

I'm still working with my mechanic to try some of the other things mentioned previously in this thread but I'm now hesitant as some of those options will be expensive.

Thanks in advance for any comments.

 

The oil filter is in the return line, between the dry sump pump and the oil tank. Even if the filter blocked all flow, it wouldn't make the cap pop out at high RPM.