Debo18D

Have been reading as much as possible and posting as little as possible as I work through these subjects learning as much as I can. I appreciate everything that I have picked up from you guys. In my quest to understand things better I have some questions:

I have read alot about small bits of debris of one kind or another "clogging up the oil passages". Just where, and how small are these oil passages? What are we talking about here? 1cm? 5mm? 2mm? Smaller? Does anyone have any pics or is there a specific location on the M96 where the oil passages are necked down to cause this atheroscler-oil-sis? And why did Porsche design them this way? to provide back pressure for the system? to decrease demand by only applying lubrication to the critical parts?



Cheers,

D.

wyovino

Are you sure you're not thinking about coolant passages? I've not seen any threads about clogged oil passages. Coolant passages on the other hand can be blocked by very small particles that may come off a failed water pump.

DBJoe996

Read less...drive more. Change oil/filter often and you won't have to worry about your oil passages.

wyovino

Passages? We don't need no stinkin' passages.

Dans996tt

My wife's Boxster would blow the cam gear plug out and the shop found the oil return hole in the valve/cam cover plugged because the previous shop had used too much sealant.

Dan

Debo18D

Pretty sure I didn't say I was worried about anything. Quite the opposite actually. And I have logged a little over 2500 miles in the last 60 days so I think I have that covered too. My question was purely informational and educational in nature.


Cheers,
D.

Byprodriver

Debo, thanks for studying 1st before asking questions that have been covered many times like most "newbie's".
Pressurized oil passage size in the M96 crankshaft is about 3.5mm diameter & stays close to that thru out most of the engine to maintain pressure. I don't have any closeup pic's but maybe you can see the holes in the shiny sections of this crankshaft on the far right.

Debo18D

Thanks Bypro. It makes much more sense now and that is exactly what I was looking for. I appreciate the pictures as well. It really starts to illustrate that part of the oil system's characteristics. I would imagine there are some counterpart passages in the block also. Good to know.



Cheers,

D.

george_west

Clogging oil passages isn't really an issue if you have a properly working filter. Spin-on filter adapter solves factory bypass problems. However, clogging oil pickup (upstream of filter) can be a problem. This can be caused by excess sealant, broken chain guide pieces, basically any debris in oil pan.

sfv_rider

IMO, the oil passages most likely to cause trouble are in the lifters. A very small bit of debris can clog a lifter, and it is unlikely to wash out.

Byprodriver

This is very true & happens often, there is no exit hole! Another good reason to change oil every 5,000 miles or year whichever comes 1st!

Byprodriver

Yes that's correct.

Schnell Gelb

Those who dismiss this issue probably have never rebuilt an M96 with their own grimey ,oily hands.Nor have they winced at the cost and complexity of the task. Note that at least one of the Posters above has done so .He has the cred.
You'd be amazed at the places you find deris a.k.a. FOM and the size of the pieces. Bits of clumsily applied silicone sealant floats anywhere. Chain tensioner pad debris is smaller but can be in chunks. There is always some aluminum shedding.Some of this is almost dust size particles but they coalesce in some circumstances. Drop the sump plate and inspect. But the real problems are elsewhere. Is flushing effective? Never tried it but I suspect it may dislodge otherwise benign lumps ? So do it twice ?
The Factory oil change interval was the worst contributor. If in it's early life your M96 had the Factory spec 15k mile oil changes and 30k filter(!!!)changes, the problem was created long before you took over .And it may be too late to remediate until you dismantle the engine to repair it. 5k Oil(the right stuff!) and filter changes are cheap M96 Life Insurance.just mho.

Macster

My advice would be to if you really want to know what these oil passages/galleys and oil feed holes in various parts look like pick up a copy of Bruce Anderson's Porsche 911 Performance Handbook.

There are a lot of pics and discussion about the Porsche flat 6 oiling system. While the bulk of the coverage is on the air cooled engines from what I can have seen the water cooled engines share a lot in common with the air cooled engines in this regard.

You'll see the cast in oil passages in the block, and the drilled (and chamfered) oil holes in the crank and rod journals, the piston oil jets, the holes that feed other bearings.

The oil passages/galleys have to be rather large to hold sufficient volume so the oil holes the passage feeds even those farthest away from where the oil from the main oil galley or even the pump enters the passage/galley are not starved for oil.

From what I have learned over the years I don't know how small the oil passages/lines/holes are in the VarioCam actuator but the smallest oil holes I know about, have seen with my own eyes, are those that feed oil into the valve lifter bodies. The pre-VarioCam Plus intake/exhaust lifters have a hole diameter of pretty close to 1/16th of an inch.

The VarioCam Plus intake lifter bodies have 2 larger holes that look to be 1/8th of an inch in diameter. The center plunger that slides inside the outer housing has a 1/16th inch through hole.

BTW, I have one of each of these lifters at my work desk and just put a rule to each of the oil holes.

I do not know how small the piston oil jet holes are. From Bruce's book they are not large but even so with 60psi (or more) oil pressure a small hole can flow a good amount of oil. And the oil jet will reach the underside of the piston even at hot idle. The exception is unless the hot idle oil pressure drops too low in which case a pressure valve closes and cuts off oil to the jets.

In almost all cases the oil demand is limited by the bearing size/clearance. The main/rod bearings run with approx. 0.001" of clearance. This dimension is pretty thin, thinner than a sheet of printer paper.

To put it another way all that keeps the main bearing of the crank from touching the main bearing of the block is a film of oil that surrounds the main bearing and is 0.001" (or a bit less) thick. (From my engine rebuilding "days" I forget the clearances of the main and rod bearings but it ain't much.)

In the case of the piston oil jets the amount of oil these deliver is primarily restricted by the size of the oil jet hole.

Similarly with say the valve lifters the amount of oil that manages to work its way past the lifter body and the bore in which it resides (and goes up and down in) is limited by the sliding fit clearance of the lifter with its bore. I dare say this clearance is probably less than 0.003".

IOWs, just a film of oil around 0.0015" thick (or a bit less) surrounds the lifter.

Be aware that in the Porsche engines there is no oil feed hole in the cam lobe to lube the lobe to lifter interface as the lobe wipes across the face of the lifter. All the oil these get comes from the oil that seeps out around the lifter bucket. (Although I would hazard a guess fully up to temperature and at higher RPMs and oil pressures the oil does more than just "seep" out.)

(As an aside, this method of oiling the cam lobe/lifter bucket is an argument against running a real "heavy" oil or a real "light" oil. Too heavy an oil can have insufficient oil seeping out around the lifter bucket. Too thin can have too much and affect the performance of the lifter and its zero lash adjuster. In both cases at higher RPMs there is a splash/oil vapor aspect to the cam lobe/lifter bucket face being properly lubricated and cooled and by deviating too far from an approved oil one can possibly cause this splash/vapor lubrication behavior to be negatively affected.)

Get Bruce's book. It is a good read and one can learn a lot from it. While I have some engine rebuilding experience -- Datsun, Dodge, Ford, Chevy, Chrysler, H-D -- Bruce's book helped me better understand the Porsche engine.

I also have a book on Ferrari's F1 engine (the V10 from some years back) which covers the engine internals (among other subjects) and this is a good read too.

Here's a link to a nice write up about F1 cylinder head design and you can get a feel for some of the oiling issues at least in the head/cam area.

http://www.f1technical.net/forum/viewtopic.php?t=15385

Debo18D

That is great information guys. Macster I have read your post 3 times and need another few times before I have a better handle on it. I will look for Anderson's book soon. Next written word for me is parts of the Porsche 996 Essential Companion. Then I will reach deeper. Thank you so much for the time you guys take in your responses. I don't take that lightly.

Now to finish polishing my wheels and adjust the seats so the twins can fit in the back for the PCA drive tomorrow morning. Looking forward to some amazing bbq out in the Texas Hill Country.



Cheers,

D.