Excessive oil through crankcase breather

Vintage914Racer · 07-22-2013, 06:29 AM

Long story short I had the engine rebuilt for my 914-6 track car two winters ago and have participated in 2.5 race weekends since then. I am getting excessive oil through the crankcase breather --- like over a quart a session. After my first event I did a leakdown test and all cylinders looked good. At that point I thought maybe I simply overfilled the oil and moved on to my next event. This past weekend at Road America I encountered the same issue. This time around there was so much pressure that it blew the house of the crankcase breather flange and reenacted ole faithful through my engine lid. Needless to say I'm not happy. Short of bad rings, what else could cause this? Anything?

I do plan on doing another leakdown test this week...

911pcars · 07-22-2013, 03:37 PM

All of the below is a personal guesstimate:

Explore historical issues with windage in the 914-6 oil tank. Does oil (excess volume or G's) cause it to climb out of the tank into the vent hose?

Are you venting the tank adequately? As in providing enough area to reduce oil velocity and separate oil from vapor/unburned gas? BTW, most 911 engines throw much oil at the crankcase breather. Thus, the normal vent exit is performed at the oil tank where high velocity oil has a chance to slow down and separate from blowby.

Do you use an adequately-sized catch can between the tank and the engine intake (or atmosphere)?

A passing leakdown test confirms adequate compression ring sealing. Check.

Under a longish, high G section of track, a large dollip of liquid oil could temporarily block a vent path allowing enough crankcase pressure to build up (esp. @ high rpm) and escape through the weakest link of the engine gasket/hose sealing surfaces.

My best guess.
Sherwood

neilca · 07-22-2013, 04:17 PM

The breather moves an enormous amount of oil due to it's proximity on top of the crankshaft. I use a -16AN line from the breather back to my oil tank as if it were a another return line. Notice my return line is only -12AN. The tank breather hose vents from the center core of the tank.

My car use to puke tons of oil also until I replumbed it.

Hope that helps,

neilca

Vintage914Racer · 07-22-2013, 05:00 PM

Thanks for the input. My oil tank is mounted in the front trunk area. If I run a line all the way up there will oil make up on its own? Seems like a long ways to move.

911pcars · 07-22-2013, 07:10 PM

Quote:

Originally Posted by Vintage914Racer

Thanks for the input. My oil tank is mounted in the front trunk area. If I run a line all the way up there will oil make up on its own? Seems like a long ways to move.

Should work if properly plumbed. Factory race cars (e.g. 935's) all use front-mount oil tanks with the necessary venting and return plumbing, sometimes through one of the roll cage tubes.

Sherwood

Vintage914Racer · 07-22-2013, 07:33 PM

How do you define properly plumbed? I would plan on having a -16 bung welded to my tank with aeroquip running from front to back. Is there any logic that says the line should slope upward or downward to the tank?

911pcars · 07-22-2013, 08:46 PM

Quote:

Originally Posted by Vintage914Racer

How do you define properly plumbed? I would plan on having a -16 bung welded to my tank with aeroquip running from front to back. Is there any logic that says the line should slope upward or downward to the tank?

I'm afraid that's beyond my pay grade. Research how Porsche and more contemporary racers do it. This might help:

https://www.google.com/search?q=911+remote+oil+tank+race+car+circuit&client=firefox-a&hs=Voo&rls=org.mozilla:en-US

fficial&source=lnms&tbm=isch&sa=X&ei=8-7tUYzbA6H7igL7jIGYDQ&ved=0CAcQ_AUoAQ&biw=1037&bih=925#client=firefox-a&hs=09T&rls=org.mozilla:en-US%3Aofficial&tbm=isch&sa=1&q=914-6+race+car+dry+sump+oil+circuit&oq=914-6+race+car+dry+sump+oil+circuit&gs_l=img.3...13737.22465.0.27168.12.12.0.0.0.0.101 .945.11j1.12.0....0...1c.1.21.img.ZEbJ2t8v3h8&bav=on.2,or.r_qf.&fp=28b6e1a417ebf061&biw=1254&bih=925&imgdii=_

and......
Tech Advice - Trunk Mounted Oil Tank - Matthias Hoeing Sportmotoren

Sherwood

johnman001 · johnman001's Garage

We started having this exact issue 3 seasons ago. It lead to a full rebuild (not needed), then another full rebuild to change oil pumps (again not needed). We too were at Road America when this started to occur.

We have been running the car with front oil tank and just a breather for around 18 years on the track then 3 years ago started having this blowing oil issue.

We ended up running the breather up along the roof and down to the front mounted tank. I see a lot of race cars set up this way. We contacted Bruce Anderson and several others with this issue and they all said to vent to the tank. Believe it or not, oil does travel through the breather all the way overhead and back to the tank.

I attribute it to the Carousel at Road America and running down hill into turn 5 at Road America. The down hill into 5, I am braking after cresting the hill and doing the downshifting, but there is a lot of engine braking as I don't just step on the clutch and only brake with the brakes. The carousel is taken nearly flat out in 4th, then a brief lift for the kink. I believe that oil runs away from the oil pump scavenge pick-up in the carousel and the crankcase fills with oil. We also have experienced the excessive blowing of oil at Putnam Park, but we rarely saw it at Heartland Park (track runs counterclockwise).

To this date, I don't know why it is happening, but it seemed to start 3 years ago for us, and it does not go away.

I do know that I have been pushing the car harder the last 4-5 years in attempts to keep up with the newer generation of cars from Porsche. It gets harder each year since the new cars out of the box get faster and easier to drive. Too many computers control the modern cars (IMHO), and it feels great when they cant get away from a lowly 914. (I tell them it came this way).

Vintage914Racer · 07-23-2013, 09:25 PM

Quote:

Originally Posted by johnman001

We started having this exact issue 3 seasons ago. It lead to a full rebuild (not needed), then another full rebuild to change oil pumps (again not needed). We too were at Road America when this started to occur.

We have been running the car with front oil tank and just a breather for around 18 years on the track then 3 years ago started having this blowing oil issue.

We ended up running the breather up along the roof and down to the front mounted tank. I see a lot of race cars set up this way. We contacted Bruce Anderson and several others with this issue and they all said to vent to the tank. Believe it or not, oil does travel through the breather all the way overhead and back to the tank.

I attribute it to the Carousel at Road America and running down hill into turn 5 at Road America. The down hill into 5, I am braking after cresting the hill and doing the downshifting, but there is a lot of engine braking as I don't just step on the clutch and only brake with the brakes. The carousel is taken nearly flat out in 4th, then a brief lift for the kink. I believe that oil runs away from the oil pump scavenge pick-up in the carousel and the crankcase fills with oil. We also have experienced the excessive blowing of oil at Putnam Park, but we rarely saw it at Heartland Park (track runs counterclockwise).

To this date, I don't know why it is happening, but it seemed to start 3 years ago for us, and it does not go away.

I do know that I have been pushing the car harder the last 4-5 years in attempts to keep up with the newer generation of cars from Porsche. It gets harder each year since the new cars out of the box get faster and easier to drive. Too many computers control the modern cars (IMHO), and it feels great when they cant get away from a lowly 914. (I tell them it came this way).

This is reassuring. I was in a real bad funk coming out of the weekend thinking that the engine would have to be torn into. I still think it is strange that it happens on some engines and not others. My last engine was not an issue at all, whereas the previous one spewed moderate oil. I attributed the first engine to being worn out. I pushed the previous just a much as the current engine, but do have a new case with a bit more displacement now.

At any rate, I will plumb a vent with Aeroquip to the front tank and assume this will take care of the problem. I'm currently running -16 oil lines so I assume I should run the same for the vent line.

I'm still going to do another leakdown while I have the car up on the lift and am poking around, but am sure the results will come back fine.

johnman001 · johnman001's Garage

What is your history with the car? My dad bought ours new in 74. I installed the -6 in 1991-ish. Our car has been track only since 1988.

Like I said, our oil spewing issue only surfaced in the last 3 years. It seems to have corresponded to the change in oil to Brad Penn. I'm having second thoughts about that oil as it seems "dirtier" even new and it does not like to pass through the Canton Mecca Oil Filters as well as others. (Have swelled up many C-M filters since the change to Brad Penn).

Our leakdown numbers always did look good, but the first suggestions that we heard, were like yours seemed to have been (piston ring blow-by), but the leakdowns never suggested that, then someone suggested it may be a scavenge issue, so we changed oil pumps. (that was an expensive thing to do when the end result was still throwing tons of oil)

I suggest running the breather all the way to your front mount tank then venting your tank. My next track 914 build will have the tank closer to the crankcase vent (probably a fender mounted tank).

Yes, the factory breather hose I believe is 1" (or -16). I used 1" OD metal tubing and tied it to the Passenger Side roll cage and into the front trunk. I followed the roofline to get the tube as high as possible, but we still get oil returning to the tank through that breather.

Vintage914Racer · 07-23-2013, 09:50 PM

Car has been a race car since 1972 and has seen a number of setups throughout the years. I've been racing it since 2000. I just made the switch from bias vintage mandated tires to super sticky radials and I'm sure this might be a partial factor. They are significantly stickier particularly through the kink where I am able to hunt down any car I've encountered there. It's interesting what you mention about Brad Penn oil. I switched to Penn with the new engine and perhaps I'll try another brand. I too have recently seen distorted CM filter cartridges that seem to align with the switch. I was running Royal Purple before. What are you running now?

docrodg · 07-24-2013, 05:47 AM

You don't need blowby to spew tons of oil. With a good ring seal the pistons are pushing a lot of air on their trip toward the crank and it has to go somewhere. Add foaming from the crank and you get even more oil puking out of the breather. If you have larger pistons and rev high you will spew oil more than a stock engine. Race oils don't have as many additives that contribute to foaming and are formulated to run in higher heat conditions so that will help. You may try a puke can in line to the tank to assist in condensing the mist as well.

Lapkritis · Lapkritis's Garage

I believe Docrodg is on the right track here with the oil type and foaming. You'll have quite a froth going with high rpm and this is where the oil type will make a difference. I'd recommend an oil type more advanced and engineered for racing such as a Mobil 1.

My additional $.02 : The absence of a condensation screen in the breather won't help keep oil from the line. Many modern engines have screens that look like the coarse stainless steel wool inside the breather vent to prevent liquid from traveling out. You would need a mechanism such as a cross of screws to prevent the media from falling into the case but would likely help the situation. I'd recommend something far more coarse than this to prevent pressure backing up but here's the general idea:

racing97 · 07-24-2013, 08:12 AM

Not discounting engine condition the oil gathers around the crank and the motion gathers it until the oil out weighs the centrifugal force. On spool up at around 6000 or so it lets go and enters the breather tube with a bit of inertia. Clear surgical tubing is the best way to observe this mass, oil just travels back and forth in the tube from the tank to the motor and becomes a nuisance if the Hose drops lower than the engine at any point in the assembly. If your system did not act up before something has changed in the assembly (oil tank and lines) and or you may not have noticed it with dark tubing.

rgards

docrodg · 07-24-2013, 08:53 AM

Some puke cans have a coarse steel wool stuff in them to promote the oil to drip then it is just siphoned from the bottom back to the tank by gravity. Trick is to mount the can just high enough to encourage the oil to go to the tank without making it difficult for it to go to the can from the breather. Closer to the breather is best, but can be more remote. Lines should only be as long as needed to attach, slack just does what racing97 mentioned... traps oil.