Leaking valve covers

I've seen this in a lot of 912's and 914's. I had it on my own 912ULS. I tried everything to make the bottom of the valve covers stop oozing. They never dripped just oozed so if you wiped the bottom lip of the cover it had oil.

I tried 4 new sets of "O" rings. No Good. I tried torquing  to a slightly higher bolt torque. No good. I tried to sand the face of the valve cover a tad and make sure it had no high or low spots. No good. I tried Loctite 598. This helped some.

You can try these one at a time and see if anything helps you. I do know that sometimes one of these will work, but not all the time. 

From my experience with hydraulics we've found it's best to install "O" rings dry.  Clean all surfaces free of oil when installing.

mb

Hi Sam

First, check the cover to be sure it is not warped at all.  The O-rings are designed to be put on dry however they usually need a wipe with some lithium grease first and then with a lint free cloth clean off any excess before you put them in the cover.  This will leave them shiny and the outer edge supple to allow the O-ring a better sealing surface.  The internal O-ring should get the same treatment.  Remember that the that this is not a gasket, it needs to have the crankcase pressure inside expand it to seal correctly.  Indeed of crankcase pressures are too high they may well weep so it might be something to check if all the normal things fail.  

I am not sure why you changed them but if this engine had an overheating event it is possible that the sealing flange on the head has warped.  In that case there is little you can do to correct this other than remove the heads and check for hardness.  Are all 4 leaking or just a few?  

In a pinch I have used Loctite 598 on them however this is usually covering up some damage or other imperfection on the surface of the sealing flange or in the valve cover itself.  As Roger pointed out this is more tribal knowledge and not a Rotax recommendation. Michael is right in that the O-right should seal without anything special.  

O-rings function by having pressure react on one side of the ring.  This pressure will push the O-ring into the groove and gives you the seal unlike a gasket that works by simple compression.  

Cheers

The motor was short blocked at 800 hours due to crankcase crack and fretting and oil is seeping from the bottom of #3 & 4 cylinders at the cover. I’ll try your suggestion of the light lithium grease instead of motor oil and if it’s still leaking I’ll try some Loctite applied to the cylinder head.

Want to report that after applying Locktite to cylinder heads 3 & 4, the amount of oil leaking was cut by half. Perhaps I’ll do the other cylinders next time I remove the cowling.