CaymanPower

Doug,

Let me clarify this better for you:

1. The smoke was ALSO occasional in my case and became more infrequent as the outside temperatures got cooler;
   
2. The amount and long-lasting smoke ONLY became that apparent after I rerouted and split the exhaust tailpipe. Before that, the smoke was diluted by mixing into the exhaust muffler with the 'clean' exhaust gas coming from the other side of the engine (bank #1). With the OEM tailpipe there's only one way out for all the exhaust gases (see pictures above), therefore they mix together and dilute each other reducing the amount of visible smoke;
   
3. Before the pistons replacement I did NOT have high oil consumption.

Do you understand this?

Please, next time you visit the dealer ask for a borescopy test (camera inserted to get cylinder images). If the dealer refuses to do it go to an indy shop (specialized in Porsche engines) and have it done. This is not an expensive test and it can give you a clear view, literally, of what is going on inside your engine.

I have good reasons to believe that you have the same problem than me.

Of course, you can have your exhaust tailpipe rerouted and split like I did and then you will know for sure! An indy shop will do it for you.

Boxster in my Future?

It will be another 6 weeks before the snowy season is over and the car comes out of storage. But I will follow up on the borescopy test when I take it in.

Doug

CaymanPower

The following videos of others 2.9L engines (a Cayman and a Boxster) just show how my engine's exhaust smoke occasionally looked like (before I rerouted and split the exhaust tailpipe). It was the EXACT same thing with my Cayman!

Doug,

Does it resemble, in any way, your 2.9 exhaust?

If so, then you have the same problem that I did. The pistons replacement cured this smoke and after 10.5k miles I never ever saw ANY exhaust smoke again.

The exhaust smoke in any of these videos is NOT normal!!! This is OIL smoke (you can see the blue haze)

2.9 Cayman:

2.9 Boxster:

CaymanPower

Since you say that sometimes the smoke was very noticeable it's reasonable for me to assume that the smoke you are talking about quite ressembles that of the above videos.

What you need to know is that Porsche dealer will keep on telling you (like in my case) the smoke is normal.

At the very best, they will perform the DME reflash per Porsche's 2009 TSB which does NOT solve the problem but tries to disguise it instead. That's what very likely happened in your 1st oil change (at about 6K miles) - besides changing the oil they reflashed your engine's DME (you can check this out, just give your dealer a call). And unfortunately, that's how far they will ever go (without further evidence from you) regarding this smoke upon startup issue.

Thus, you need to show them that there is an incongruity as far as 'the smoke is normal' claim is concerned (like a TSB that doesn't solve the problem wouldn't be enough!).

What you have to do is what I did... reroute and split the exhaust tailpipe and then ask them this simple question:

If the exhust smoke is normal with flat engines how come ONLY half of the engine smokes - bank #2 (rear view left side)?!

Porsche knows perfectly well, as I know, that this is NOT normal and that this is NOT an isolated case - if I count my two 2.9 Caymans, your 2.9 Boxster and both the 2.9 Boxster and the 2.9 Cayman from those videos, we have already 5 known cases here! Now just imagine all those cases where the owner doesn't care because he/she is told that the smoke is normal?!

There's a reason for Porsche to have dropped the 2.9L engine altogether in favour of the 2.7L engine (same power figures) in the new upcoming 981 Boxster/Cayman when, at the same time, they kept the 3.4L engine from the current 987.2 Boxster S/Cayman S and didn't reduce the displacement in similar fashion to 3.2L.

What is more striking still is the fact that by virtue of these engines design the bank #2 cylinders are forced to deal with the highest engine temperatures, therefore, bank #2 ALWAYS seem to be the problematic one!

CaymanPower

Unfortunately, replacing the pistons isn't good enough because the ALUSIL cylinder bores must be honed or else the new rings will never seat properly and you will end up with high oil consumption like I did, albeit without the smoke upon startup issue! Honing these bores properly is a HIGH precison job as the tolerances are VERY tight and NO Porsche dealer is up to the task. In my case, the bores weren't honed and I highly doubt that they were properly tested for 'ovality' also, but I expect that the bores are likely less susceptible to distortion the engine being of the 'closed deck' type!

So, a NEW engine is the only good option for this smoke issue.

CaymanPower

You understand now why this is an inconvenient truth... because a new engine is required!

Next, you can see ALUSIL (a silicon powder is mixed in to the aluminium alloy when casting the block) cylinder bores from bank #2 where the smoke was coming from. They looked good and didn't have any scratches deep enough to catch your nail on:

Cylinder #4



Cylinder #5



Cylinder #6




In the second picture from each cylinder, one can clearly see two parallel lines that run the length of the whole piston travel showing the side where the piston squeezes against the cylinder wall to transfer the linear motion of the piston into rotating motion of the crankshaft through the con-rod - the thrust side!

Boxster in my Future?

On occasion, my exhaust is pretty close to what you see in those videos. On most other occasions, there is virtually no or absolutely no smoke. How would you explain that? I am also uneasy about this since your post has not attracted others to chime in which leads me to believe most 2.9's don't have this issue. Yes?

Doug

CaymanPower

Doug,

First of all thank you for your thoughtful questions!


As I've already said the exhaust smoke in my Cayman was ALSO occasional. It's the exact same thing.

By evidence gathered from my experience with this issue and comprehensively presented here (and elsewhere) the problem arises, contrary to my expectations, from the excessive initial bore to piston clearance. Since these engines smoke upon startup from new there IS some issue with the factory size/shape tolerances of the pistons.

So, why is the smoke occasional and why does only bank 2 smoke?

1. The front and back of the piston pushes against the cylinder wall to transfer the pressure pushing it down into a force down the con-rod to turn the crankshaft;
   
2. The heat from the piston is dissipated through the piston rings, the oil mist that is in contact with it and the faces of the piston as it rubs against the cylinder wall;
   
3. There are oil spray jets fitted to each cylinder (see picture below) to cool the piston and these will also lubricate the bores once sufficient has been sprayed up into the piston crown area to spread out to the bore area;
   
4. So normally there will always be a thin oil film in the contact area between the piston and the cylinder wall (through which the heat is dissipated) to ensure that the two surfaces don't rub directly against each other;
   
5. Because the piston is hotter than the cylinder some clearance must exist between them to allow for piston expansion;
   
6. If this clearance is more than it needs to be to run ideally - because it has to allow for the expansion of the piston - the pistons will NOT expand enough to fit well in the bores and the ring gaps will be so large that the blow by will increase;
   
7. Allowing pressure above to blow MORE hot gases past the piston rings means burning or overheating the oil film and blow away some of the oil that should be present – increasing the friction and heating the oil even more while it has less in the area to cool the piston anyway;
   
8. Surface piston temperatures increase, the cylinder walls run hotter and oil viscosity drops;
   
9. That can result in the viscosity of the oil becoming too low in SOME circumstances and under SOME driving conditions;
   
10. The cylinder and piston lifespan will be reduced depending on how hard (higher range of temperatures) and how often the car is driven;
    
11. When the engine has stopped the pistons sit on the bottom face of the bores (through gravity) and HOT oil seeps away from the stationary piston as it shrinks in SIZE on cooling - the oil tries to drop or flow down to the bottom of the bore.
    
12. A tight clearance will keep some oil in the gap in between the piston and the bore (due to surface tension) but if the gap gets too big it will allow the oil to slide away leaving the top of the piston (the thrust face on bank 2) - the oil film being too far away from the cylinder wall to prevent it draining down to the bottom of the cylinder as the engine cools down;
    
13. Due to the extra piston clearance, the space left gradually fills up with carbon and congealed oil sludge (from blow-by);
    
14. Bank 2 thrust side is the MOST vulnerable because when the engine is running, cooling is less effective in there - the coolest coolant enters under the cylinders first and as it travels upwards and picks up the heat the temperature rises, by the time it reaches bank 2 thrust side its cooling potential is already greatly diminished, thus the thrust side on bank 2 will always run hotter than that of bank 1 (remember that the cylinders are horizontally opposed and the thrust side on bank 2 corresponds to the upper cylinder wall whereas on bank 1 it's the lower cylinder wall);
    
15. If, OCCASIONALLY, enough congealed oil sludge and carbon exist around the area that there is a gap between the piston and the cylinder wall (the thrust face on bank 2) then oil, that would otherwise drip into the piston through its drain back holes (see picture below), will drip onto the cylinder bore on resting the engine and smoke will be the result from burning it upon the next startup.

Piston oil jet:


Piston's oil drain back holes:




Doug,

Through tighter bore clearances and better heat dissipation engine manufacturers were able to deliver increased performance, lower fuel consumption, reduced emissions, better thermal balance, better thermal conductivity (cooling), faster warm up times and the ability to run with reduced coolant quality.

I don't believe that most of the 2.9's owners will ever realize that despite the oil smoke upon startup issue, which they are WRONGLY told that it is normal, simply because most of the 2.9's owners don't have anything to compare with except for the fact that they own a Porsche.

So, they don't care.

CaymanPower

In the most severe cases - earlier 2.9 Cayman/Boxster versions (MY09) - where the excessive initial bore to piston clearance IS more pronounced due to a greater out of spec factory tolerances in the size/shape of the first pistons (P/N: 9A1 103 029 63), scoring of the cylinder walls on both cylinder banks occurs with VERY low mileage (see pictures below).

Despite that, Porsche issued a 2009 TSB for the 2.9 Caymans/Boxsters, which consisted in a DME reflash, BUT only concerning the oil smoke upon startup. So, what does this reflash do after all?!

With the new oil pump in the 9A1 engines, the required oil pressure and oil volume is set for each engine operating state defined using a map in the DME control unit - depending on the engine speed, engine load, engine oil temperature and the expected change in engine speed.

Thus, the reflash mainly re-programs the DME to force the delivery of more oil volume from the demand-controlled oil pump for the entire engine map (also upon startup) in an attempt to reduce the cylinder wear and prolong the life of the engine by disguising the real problem.

Unfortunately, that's the Porsche way!


Just read the following testimonial:


Cayman gen 2 - white smoke on start up - HELP!!!


Borescope cylinder wall pics (all 6 of them on a 6.4k mile Cayman):

CaymanPower

As already explained, oil accumulates on the cylinder walls and the oil film will tend to remain in contact with the cylinder wall as the piston slides across it, so a method of scraping this oil is necessary to prevent oil from entering the combustion chamber as this can lead to detonation which in turn increases carbon build up and raises both piston and oil temperature.

There is three rings on the 2.9 engine's piston - top compression ring, second ring and oil control ring. By todays standards, the second ring serves more as an additional oil control device than it does as a compression sealer (about 85 to 90 percent oil control and only 15 to 10 percent compression control), so both the oil control ring and the second ring perform the scraping function despite the fact that only the oil control ring redirects the accumulated oil to the drain back holes drilled in the piston when the engine is running.

In an attempt to justify the random nature of the smoke upon startup some will say that is due to the piston rings rotation and their end gaps occasionally getting aligned at the bottom of the cylinder bore allowing some oil seepage past the rings (through the end gaps) on resting the engine.

Well, the following video just shows that the second ring (first 6 seconds) in the 2.9 engine is unable to rotate because there is an anti-rotation pin in the ring groove between the ring gap extremities at the top of the piston (around half past 10).

So, the 'aligned ring end gaps at the bottom of the cylinder' theory can't hold up in this engine!

San Rensho

Read part 5 on this page when you have a couple of hours to kill. Much will be revealed.

http://www.hartech.org/buyers.html

CaymanPower

I already know that article and although most of my findings pretty much match their explanations (upon which some of my own explanations are based) I don't agree with all its content.

For instance, they say (page 22) and I quote:

In the 2.9 Caymans/Boxsters the oil squirters are located in the top of the cylinders (like in the older air cooled 911’s) aimed so that the spray is directed at the underside of the piston to cool the piston crown. Thus, their theory regarding the oil squirters favouring bank 1 doesn't hold true for the 2.9 engine (see picture below).

Their article is about the 996 3.6, 997 3.6, 997 3.8 and Cayman S 3.4 engines.

My thread is about the 987.2 2.9 engine (9A1). But nevertheless, you can clearly establish a pattern common to all water cooled Porsche boxer engines.


Another example, they say (page 64) and I quote:

That simply is NOT true. The piston oil drain back holes provide a scavenging method for the accumulated oil in the cylinder to drain back into INSIDE the piston away from the bores, plain and simple.


Still in page 64, they say and I quote:

If this explanation was valid then why only SOME engines would do it while there are others (like mine after the piston replacement) that NEVER smoke upon startup even though their engines are STILL horizontally opposed?! I'm sorry, but this theory also doesn't hold true.

San Rensho

What do you think about Hartech's theory that when , Porshe changed the headgasket design, restricting the coolant flow to cyl 6, especially, that the it led to overheating, causing ovaling of the bore and excessive oil consumption?

CaymanPower

As it has been demonstrated, the right clearance between the piston and the cylinder walls is absolutely essential in both horsepower and reliability. However, a thin line exists between too much and not enough.

Keeping a proper piston to cylinder wall clearance whether the piston is cold or at operating temperature presents a BIG challenge to engine manufacturers because as metal warms up, it expands and gets bigger. Different aluminum alloys expand different amounts for the same temperature change, depending on the amounts of silicon, magnesium, manganese, nickel, copper, and other elements that affect the expansion characteristics and wear properties of the piston.

Thus, the piston shape is designed to compensate for both heat expansion and physical forces it will experience as the engine operates.

Forces during the power stroke are greater at the thrust face than elsewhere on the piston sides. Therefore a piston is often made so that its skirt is elliptical or egg-shaped instead of round - the largest diameter being across the thrust faces. When the engine is cold, the two high spots of the piston skirt fit close to the cylinder wall preventing oil seepage. As the temperature rises, expansion causes the piston to become round instead of binding up in the cylinder. Force on the power stroke will push the piston thrust face into the cylinder wall making the piston rounder during its power stroke than it is otherwise.

Also, there is different expansion rates of various parts of the piston - the piston crown is exposed to the high temperatures of combustion and will expand more than the cooler skirt does. To compensate for the greater expansion of its crown, the piston is constructed with a slight taper - the diameter at the lowest part of the skirt is larger than the diameter of the piston crown. As the engine operates at proper temperatures, the piston shape will become round. Piston taper can have a tremendous impact on the actual clearance.

Moreover, forged pistons have less heat dimensional stability and require greater skirt clearance for reliable operation.


For all the above reasons, one can readly see how occasional smoke upon startup can result from someone messing up with the factory tolerances of the pistons size/shape.

CaymanPower

Why do you ask?