lordofwar

it was a cloudy day so I decided to pull the supercharger cover today to see what it looked like.2016 A8 2300 miles.was not a hard job,back 3 bolts were a pain,so I made a tool out of a old motorcycle 10 mm wrench that came with the bike.bent it in my vice with the help of a big hammer.made job easier. rings and gasket are rubber so you don't need new ones.got it off and like I read in anohter thread there was oil in it.cleaned it all out using qtips to get in all nooks and crannys.wiped the cover down real good and reinstalled it torqueing the bolts to 88 INCH POUNDS,not foot pounds.question,why is there oil in there and how does it get in?

bearmans

If you open the dump valve/plate seen in the front of the super charger, you will see a silver fitting in a rubber o-ring in the bottom of the super charger. That is part of the positive crankcase ventilation system (PVC). It takes the excess pressure built up by the underside of the pistons on the down stroke and vents it to the super charger where it is burnt in the cylinders. Same as the old PCV valves that were in the valve covers but the valve is built into the L.O.M.A. (lifter oil manifold assembly) or valley cover. Without the PCV system, you would be blowing out front & rear crank seals. When you reinstall the super charger, torque to 10 NM +- 2 NM. Then, go around a second time. This makes sure the seals are properly seated.
Barry

Busa Dave

WOW--yours looks pretty clean. You are lucky. Mine was worse and it had about 1300 or so if I remember. Make sure to check the CAI..

davepl

I don't want to be overly pedantic but the pressure in the crankcase is not from the downstroke of the piston, as there's an equal and opposite upstroke of another piston at the same time. The volume of the crankcase does not change.

The pressure in the crankcase is created by combustion pressure escaping past the rings (blowby) and it picks up oil from windage, which is then sucked through the PCV system and ultimately into your intake path which includes the blower.

It's all by design, but oil isn't welcome in supercharged engines because of the reduction in octane it causes. It causes detonation very easily.

K B Vettin

consider adding a sealed oil catch can, I prefer Elite Engineering. it keeps the PCV system intact but the oil in the blow by catches in the can instead of boing back into the blower.

bearmans

The little bit of oil is excepted because with a direct injection engine, you don't have the fuel washing over the valve stems for lubricating and cooling. Blow by is minimal. The pressure is caused by the down stroke of the pistons and the rotation of the crankshaft. Being a dry sump engine, there is minimal oil pickup due to windage, just pressure. It is all by design and is normal. If you had ever taken the intake off of a say, 1972 350 and looked into the intake ports, there would be evidence of oil. All normal.

lordofwar

so it is normal.should I clean it every 2k miles?what do you think will happen if it builds up?would dealer clean it under warrenty?

David@MMS

photos of the situation first post here

https://www.corvetteforum.com/forums...4-pcv-fix.html

happy to help if interested

davepl

Saying it twice doesn't make it true. There is no "pressure" created by the downstroke of a piston because there is an equal and opposite upstroke. The rotation of the crank causes windage, not pressure.

But feel free to continue to believe otherwise; I've responded twice out of respect for the facts, but I'm not passionate enough to force anyone to believe them.

Not ideal but absolutely normal. Dealer will not "fix" it because it's normal.

Rookieracer

Factually, it depends if it is an open crankcase or segmented. Even in an open bulkhead crankcase, air displaced by one piston has to move from one part of the crankcase to another, so there are pressure differentials when measured in different parts of the crank case.

Hence the reason in racing engines we use over-sized dry sump pumps and vacuum pumps in order to create negative pressure in the crankcase which reduces these parasitic pumping losses.

I do agree, that the majority is getting by the rings...

dtgaskal

Bearmans builds the engines at Bowling Green. I'm going with his way of thinking. Over 5000 miles on the 14th z06 made in 2015 and I never pulled the cover because it still runs like a beast.

Rookieracer

Fyi.

capevettes

Barry, I appreciate you chiming in on this. It's nice to see someone who builds them have the interest and take the time to contribute here.

Thank you

Redc8z06

According to GM adding this will void you warranty. Beware...

lordofwar

that is why I will pull my cover every 2500 miles and clean it.no big deal.

spearfish25

I guess the real question is whether the valve deposits come from the oil in vapor form or the pooled oil accumulating enough to finally get to the valves in liquid form.

yz250fPilot

His way of thinking is incorrect - do a Google search on the topic.

The lesson-learned is that just because someone assembles engines doesn't necessarily imply they know how they operate - as is the case here.

As correctly stated earlier, the crankcase pressure is generated from blowby past the rings.

Twowheelin_wildman

So that's what that rascal looks like inside.

Bill Dearborn

Well the first thing you have to do is verify there are deposits on the valve stems. GM has put several million DI engines on the road over the last 9 years and they don't seem to have a problem with oil deposits on the backs of the valves. The big complaint is with the V6 engines that seem to lose their timing chains on a fairly regular basis. I can't say for certain but I suspect GM has designed their engines differently to reduce problems with oil deposits on the intake valves. My neighbor just cleaned the deposits off the back of the valves on a family member's VW that had about 80K miles. It had started running rough. Even on the cars noted for having the issue this seems like a long term problem not a short term problem. Very few first, second or third owners of C7s will ever keep the car long enough to see a problem if there is any. Most Vettes with 80K miles are 15 or more years old.

Bill

Mad Dog 24

The oil out my Colorado speed \ Elite can after 2k miles and a couple of track days. These cars push major oil at the track at WOT! I just as soon empty my can every so often than let it coak up on my valves.




I still get some oil residue under the SC cover but nothing like before the can.