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Oil return under umbrella valve.

18K views 24 replies 8 participants last post by  naknekpete 
#1 ·
Was wondering what a few of you (especially Hillside, Prodrag, etc.) thought about drilling those holes out a bit more. Saw some talk about it one a forum. They seem to think it will help out with the blow by and oil getting into the breather and dropping down side of bike. Especially on bikes that have added bigger cams.
Would like to hear what you think on this matter.
Thanks for your time.


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#2 ·
Not sure how frequent they check in...

Shoot Scott(Hillside) or Kirby(Prodrag) a PM... more likely to get a notification.

Also, Scott I hear is always willing to take a call at the shop. :thumbs
 
#4 ·
i drilled mine out in my evo motor, it helps them drain back quicker, also you may want to use a stepped bit to finish the hole, it will help them drain.
 
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#6 ·
The purpose of the rocker cover umbrella valves is breathers not oil returns. If the holes are drilled larger more oil will escape out of the breather and into the air cleaner or where ever the breather hoses are routed. As little oil as possible should escape through the breathers, only an air oil mist.
 
#7 ·
I believe the O.P. was talking about the oil returns themselves and not the actual umbrella valve, as you are correct on the umbrella valve being a breather, however there is a little hole in the plate that is meant for an oil return, under high rpm you can actually start flooding the rocker box with oil because it cant return fast enough

if you rev high or run it at a higher rpm for sustained periods it is helpful to open the oil return up, again i did this to my evo 80 motor with a 7k redline, i also dropped my breather lines to the ground and not back through the intake, as it is dirty air along with being warmed from the motor and any possible oil that may pass through, it was only routed through the intake for emissions purposes
 
#8 ·
I re-read the OP's post and he was referring to the umbrella valves as oil returns. The Umbrella valves are breathers only, no oil return from the umbrellas to the crankcase. Any oil that goes through the umbrella valves goes out to the air cleaner or the atmosphere. They are called "breather heads".
 
#9 ·
I was referring to the two holes "under" the umbrella valve.
Dark horse is right on with what I have heard. I'm just wondering if it is a good thing to do and if there are any negatives associated with doing it.


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#11 · (Edited)
I did this to my softail project when I had the rocker boxes off.

I drilled mine to 3/32"=0.094" I think stock is .070"

I spoke to a friend who works at a dealership who said there's no harm, I'll let ya know how I make out when the bike is finished.

Also worth noting, when I replaced my head breathers, HD changed the breather design. The original was cast aluminum. The updated ones are stamped steel and come with shorter bolts. I noticed the updated ones had a larger filter element too. Not sure if that will help or not, but its worth mentioning.
 
#12 ·
What I had read and what Prodrag said, most drill the hole to 1/8" or .125. I think I drilled mine to 7/64' or .109.
I've got about 1500 miles on it so far. Checked it once and had a little oil around the bottom of my air filter frame and there was a couple dark spots in the bottom of the filter element. Nothing leaking out on the motor itself though. But I have not run the bike at high rpms for a long period to speak of. Was on interstate once running about 80 for 15-20 miles, with a short stint of about 4-5 miles of that at 100 (was catching up to buddies). I didn't check it till several days after that though.
 
#13 ·
If you only have 1500 miles, the rings may still be seating too. creating a little higher crankcase pressure.

Whenever I do rebuilds, I normally change the oil at about 200 miles, then again at 1000. Then normal maintenance from there on. I'm sure others will tell you other ways, but in my eyes, its cheap insurance and gets the metal particles out of the oil from the rings seating, bearings wearing, etc.
 
#20 ·
OK ... now I see what you guys are trying to do !!!
The oil that goes thru those holes goes right back into the rocker box, not down into the crankcase. Those are overflow drains for when the breather filter gets saturated with oil.
I can see why the race guys do that because they're always running high RPMs and oil can accumulate in the rocker boxes so every little tweak can help for a race engine. For a street engine ... no difference IMO !
AND If drilling a hole larger to fix that problem the MoCo would have done it long ago !!!
If it makes ya feel better just do it, ain't gonna hurt nothing !
 
#21 ·
Hey Shmidty, have you ever seen oil drips on the side of your motor or exhaust under your breather? If so, this is caused by excess oil getting blown into the breather from the crankcase/umbrella valve. Drilling these holes out helps alleviate this.

And yes, you are correct. It is mostly only caused under higher rpms. But it also happens when traveling on the slab at higher sustained speeds. Like down I-90 through SD doing 85 the whole 400 miles. From research here and others, I couldn't find any negative to doing this. So I felt since it was supposed to help in certain situations and not hurt anything at all, I did it to my bike while I had it apart. Now would it be worth doing just to pull the rocker covers, rocker assembly and all off just to do this, probably not.

Want to start another topic? While I was in there, I also added the "Rockout Rocker Shaft Inserts". IMO, this is something worth tearing the rocker covers and rocker assembly out for. LOL
 
#22 ·
HaHa, like I said " if it makes ya feel better just do it " !
Also some high performance mods on street engines do more bad than good. Example, ya can't just throw a hot cam into a stock engine and hope for high performance !
 
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