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So looking into engine rebuild options - I have not found many informational threads to help the guy who is stuck with a 04 Cayenne S that needs an engine rebuild after it has ruined it's cylinder walls (cylinder scoring).
I have read some documentation online about the importance of proper honing process and finding a shop that has experience and desire to work with the Hypereutectic engine block and a profilometer to verify the cylinder wall finish. The machinist needs to be very familiar with the rate or removal of his chosen tooling and the abrasives chosen for this process.
Porsche likes to boast of the % of its total cars produced still on the road today - yet I can not find the piston to cylinder wall clearances for these engines. I have read the engine replacement thread. I am aware that these dimensions are not published. Jake also suggests that piston to cylinder wall clearance and extreme cold climate is the root cause for the cylinder damage. So it would seem the key to a successful rebuild is proper clearance to allow for the piston skirt expansion with out cylinder wall damage.
I am looking for piston & ring options to get my existing block bored to remove damaged cylinder wall and prepared for new pistons.
-Torque Plate required? locate or fabricate if necessary...
- Pin offset?
- Coated piston skirts?
The article about Hypereutectic engines suggested a few details:
- 3 step process Honing, finish honing, exposure
- MAN 845 honing oil is minimum requirement - Ideally filtered to 5 microns.
- No water based coolants should be used - contributes to sludge and adversely affects honing
- finish honing pass should result in 0.1 micron finish (ultra smooth or mirror like)
- extremely light honing force and XM27 elastomer based "stone" - is superior to any rigid abrasive or "stone"
- 0.5 micron Si crystal exposure height is typical - after proper exposure process
- Barrel shaped piston ring faces are mentioned..on coated cylinders
- DLC coatings for the piston rings may now be the Porsche parts in use
- importance of excellent machining geometry - cylindericity limits of 0.0005"
- cylinder plating maybe beneficial - but costly and requires shipping block off
Anyone been down this path care to comment or point me at other relevant threads I should read?
The nichrome process is going to be your best bet. Ideally, in my opinion, a set of custom hypereutectic pistons and the nichrome would be the most cost effective and durable in the long run for a stock rebuild. As for clearances.....you are right in that is no documentation from Porsche or otherwise. You need to find an experienced engine builder.
at 80K miles Engine suddenly started to consume oil (1qt per 1000 miles) in April - May and after adding a few quarts eventually fouled #6 spark plug. I pulled the plug and borescope showed cylinder wall damage. Parked it to prevent any more damage and looking to rebuild the engine.
I purchased the car used with 42K miles. It was in very good condition, Never needed any oil between oil changes. I changed the oil at 5K intervals with Mobil1 while in my ownership. Car is a daily driver so not sitting etc..
Have engine in the garage and going to pull the heads to see what cylinder walls look like. My engine failure presented pretty much exactly as Jake Raby has described in his failure mode analysis - The past winters extreme cold temperatures and the timing of my oil consumption and resulting accumulated cylinder damage in spring. No attached garage to help with temperatures.
If you are interested the last several pages of this thread get you up to speed.
The workshop manual page for inspecting piston / Ring / cylinder wear shows the following dimensions:
[NOTE - THIS IS THE VR6 SPECIFICATIONS - NOT THE V8]
base measurement in mm: Piston diameter 83.965, Cylinder diameter 84.010
measurement of wear in mm: Piston 83.925 (0.04mm smaller than base), Cylinder 84.09 (0.08 mm larger than base measurement).
The base dimensions suggest that new there is 0.045mm (0.00177") operating clearance? and the wear limit is 0.165mm (0.00649")
What am I missing - it would seem that 0.045 mm is the factory nominal operating clearance (piston to cylinder)? It would be interesting to see if these values changed for the later engines?
Last edited by matt_o_70; 04-18-2016 at 10:49 PM.
Reason: wrong specs - VR6 not V8
Bore on the 4.5 is 3.66". Or about 92.964mm. Which manual do you have? I think your looking at the wrong section. Porsche didn't publish any clearances for the 4.5.
I think Jonathan will agree that your barking up a very expensive tree to address this. The vehicle isn't worth the time, money and heartache to deal with it.
Bore on the 4.5 is 3.66". Or about 92.964mm. Which manual do you have? I think your looking at the wrong section. Porsche didn't publish any clearances for the 4.5.
I think Jonathan will agree that your barking up a very expensive tree to address this. The vehicle isn't worth the time, money and heartache to deal with it.
Is not where I wanted to be.. rebuilding the engine - I can't walk away and there really isn't anything else I'd rather have anyway.
Apparently I was looking at the V6 specifications, So odd that they publish these for the V6 and not the V8 - In the same manual.
Finally found some time to get the heads off. Cylinders 1 & 6 both have cylinder wall damage. It is a bit hard to see the magnitude of the scratches in the images, but you'd have no issue feeling the cylinder wall damage.
Cylinder 1 scoring
Cylinder 6 scoring
sending it off seems the smart repair path - calling around to engine shops - no one wants the hassel of hypereutectic engine block process.. They have plenty of other 'easy' work.
I'll be interested to see if the cylinder damage is below the piston ring lands once I get the pistons removed. Since it does appear that cylinder #6 is a bit washed down, as compared to its mates.
Notice piston #6 washdown compared to others.
I was not aware of engine consuming coolant.. but there was some coolant weepage under the plenum and down the back side of the block. No coolant ever made it to the ground - Notice the signs of dried up coolant on the engine block under the flex plate.
scuffing of block is all the way to the bottom of the cylinders.
DIY lock off plate to engage the flex plate and hold the crank - to break loose the front pulley / harmonic damper.
It did take a bit of work with an internal puller to work to free the oil feed tube from the pan and oil pump. I was able to use a $12 pilot bearing puller - with a mod to the OD of the pawls with a file to better grip the ID of the feed tube.
with a bit of work the tube comes out - to allow the oil pan to come free of the block.
I had to pick up the HF set of Deep External Torx sockets to get the bigger sizes (found e18 in the deep set only) used to hold the Main caps / lower half of the block in place.
Heads and block deck check out true - Nothing warped.
Lots of hardware, o-rings and gaskets to track down and order.. Going to work up a parts list. The dealer tells me that there is no engine gasket 'set' for the Cayenne.
A CS is worth $8-12k. A turbo is only a few grand more. Are you sure it pencils to rebuild. Make sure you run the numbers and consider that your time is worth something too.
09-26-2015, 12:11 AM
S engine rebuild - DIY repair path?
