Rubbermount_EVO Rocker cover leak fix?

[Jfart]

05 1200 custom. Engine mods are hammer performance air cleaner with horse shoe breather to environment and Vance and Hines short shots.

History: end of last riding season I noticed the bikes been burning more oil (exhaust smoke) than in the past years. Found leak where the front cylinder meets the intake manifold. Soon after it fouled (oil fouled) a plug in the front cylinder. Compression test was good. Leak down test lead me to believe the valve seals were leaking on front cylinder. I changed the valve seals and since I was that far I changed the gaskets from the base gasket up (leaving the pistons in the cylinders to pull the cylinders). When replacing the valve seals there was a obvious amount of oil inside a few seals but I can’t remember which ones. It’s not fouling lugs anymore.

Bike went back together as usual and started up good. After 20-50 miles rocker box cover (two piece) seals (cometic) started leaking in the lowest point on the front and back cylinders. Ordered new seals and tore it apart. The seal on the front cylinder sucked and was torn inward from negative pressure, the rear was just sucked in and stretched out, not torn. I replaced the seals and now 200-300 miles in, the seals are leaking in the exact same spots as before.

I’ve looked into this and it’s obviously a common issue on the early rubber mount sportsters. A lot of people complaining and dealers changing seals. Some say you need new HD seals, some say you need new rockers without the groove cut out next to seal. Some say a breather needs to be machined (I’m having troubles finding someone who has done this and documented it well enough to copy the mod).

Can anyone please send me in the right direction? What fixed your rocker cover leak? Changing just the seals obviously isn’t fixing the problem.

Was the leaking valve seal what prevented this leak or did the leak just start after taking apart the top end? I’ve gotten into the top end of my 02 rigid mount too many times without issue, this can’t be a coincidence. When I looked at the rocker cover seals after they failed the first time I was shocked to see that much negative pressure, is there an imbalance? Is the extra heat the rubber mount bikes put off part of the problem?

[Hippysmack]

Imploding gaskets point to too much vacuum in the crankcase.
Too much vacuum can be caused from;
1. Leaky gaskets (chicken or the egg thing).
Leaky gaskets can allow oil to leave the motor and/or air to enter the motor.
Too much air intake throws off the balance of pressure (more push/pull going on).
Also see 2004-2006 Rocker Box Design Change in the Sportsterpedia.
http://www.sportsterpedia.com/doku.p..._design_change
Check the lip on your rocker boxes against the pic in SP.
2. Stopped up breather valves (mesh filter cogged with oil).
3. Hardened umbrella(s) in the breather valve unit(s).
4. A stopped up air filter (if you have a filter on external breather hoses).
5. Pinched breather hose (if modded external).
6. The plastic oil tank can also be a culprit of messing up crankcase pressure. (although you'd eventually see a leak or bursting of the tank).
7. Bad crank seal (although you'd notice excess oil in the primary).

[rejeanprimeau]

Chrome cover are notorious to leak from the same spot; lap the cover on a fine sand paper glue to a piece of flat material. You have to go to aluminum.

[ReddTigger]

Originally Posted by rejeanprimeau

Chrome cover are notorious to leak from the same spot; lap the cover on a fine sand paper glue to a piece of flat material. You have to go to aluminum.

When I was working for HD we had a piece of granite countertop with a piece of sandpaper glued to it. and this is exactly what we did..


you can use plate glass or a mirror as well, but be sure the surface you're going to use is perfectly flat.

[Tomcatt]

Originally Posted by rejeanprimeau

Chrome cover are notorious to leak from the same spot; lap the cover on a fine sand paper glue to a piece of flat material. You have to go to aluminum.

+1
The chrome is slippery, the gaskets literally get squished out or in. Has nothing to do with Hippysmacks' favorite pressure flow theories, it's a mechanical issue. But you do tend to get oil leaks/seepage, gaskets pushed OUT if you block or excessively restrict the crankcase breather(s).

Originally Posted by Jfart

Some say a breather needs to be machined (I’m having troubles finding someone who has done this and documented it well enough to copy the mod).

If you're referring to drilling out the breather bolts' 1/16" restriction I'm one who's running "big bore" breather bolts as is anyone else who is running the popular aftermarket "horseshoe" external breather. It comes with "big bore" breather bolts. No oil leaks or seepage. No pushed out (or sucked in) gaskets. They work.

[Andy56]

I hope I have got this correct. I have a 2008 here and the very top cover has 2 what appears to be a silicone rubber inner and outer seal.

The front cylinder was leaking so I got new HD ones. The material has been changed to something a bit more rigid.

As the seals sit in grooves, me, I don't know how they can get pulled in or pushed out.

[Tomcatt]

Originally Posted by Andy56

As the seals sit in grooves, me, I don't know how they can get pulled in or pushed out.

Because your bike has the upgraded parts. The problem bikes were '04-'06 with chrome rocker covers.
Hippysmack references the change in his post, #2, if you had read it...

[Andy56]

Okay, thanks.

The 2008 and 2017 both have chrome rocker box and rocker covers.

Even though I don't appear to have a problem it is nice to understand these things. I might get a problem bike in the future or come across someone having the same issue.