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More than happy to shoot a pic or two with my boroscope next time I am near my car. There is no need to take apart the engine to see that there no problems. The 928 will smoke if there were issues with the bores or the pistons’ skirts were galled. As you can imagine the situation would be gradually getting worse. In my mind the proof is absolutely conclusive - the race GTS doesn’t smoke, doesn’t use oil and makes 400-odd BHP, the GTs that I mentioned are daily drivers and so is my GTS.
If you don’t believe me, I am sorry, but the shoe this time is on the other foot. We have put time, effort and money into getting this set up to work. We are happy with the end result. If that’s not enough for you - follow our lead and put your time and money into it. But I ain’t taking a perfectly good engine apart to prove something to someone on the internet...
I'm not remotely trying to offend you...just asking questions.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Greg - can you point me to the Kolbenschmit document you reference, I'd like to read it - My google search did not result in any hits. Do you happen to know if they also have Alusil sleeves for Cayenne applications?
Tear down has begun. I got the pistons out today in prep to split the block. All rod bearings look good except #5. Something got trapped. Crank has some discoloring but no grooves . Crank travel came out to be .2794, fantastic .
Bottom of thrust bearing Front face of thrust bearing Rear face of thrust bearing
Some wear on #5 at the 5:00 position
So, mains mostly look good. #1 shows wear on the lower edge. Will need to replace that one. All others look good to me. Not perfect but uniform.
Questions
1. Does the crank always show discoloration near the face of the bearing surfaces?
2. Can I just replace the one main bearing?
3. Is it ok to send the crank to a generic shop to get polished?
I would do a very careful job of measuring the crank.
From other threads Greg Brown has suggested that the cranks in the 928 are very hard to damage.and or wear.
I would not get the crank polished unless your planning on removing the dirt trap plugs, then you can tap threads and install new plugs.
depending on how this polishing is done the swarf of it can rinse down the oil port and then if its not removed,
once its running the hot oil will get it moving into the new bearings.
I did get a crank polished and it came back full of crud entailing the traps be removed to properly clean it out,
and tapping threads to fit new plugs.
Also some of the info that the main bearings are telling is that the crank damper is causing the bearings to have these marks.
So fitting an updated crank damper would be a wise move and from the looks of things all of the bearings should be replaced.
Questions
1. Does the crank always show discoloration near the face of the bearing surfaces? Yes. These crankshafts are "induction hardened", which heats the journals and the areas on each side of the journals, but not the entire crankshaft.
2. Can I just replace the one main bearing? Yes. Just don't tell the rest of the bearings that the one is new....they tend to get offended.
3. Is it ok to send the crank to a generic shop to get polished? Yes. I never allow anyone to polish with a sanding belt....only with a "Scotch Brite" belt. No matter what you do, you will need to clean the blind oil galleys out, extensively.
The piston in #4 had a nick out of one of the rings. I doubt that his was the cause of the gouges , but that is all I found.
The damage was caused by some foreign object between the piston and the cylinder head. You can see the damage from this object on the top edge of the piston.....right at the very left top edge of the piston (in the picture above.) Those "dents" on the top and corresponding "bulges" on the side of the piston are what damaged the cylinder wall.
I am hesitant to send it out for polishing. Just some discoloring. Will sleep on it for a few days. Not looking forward to try to get this galley plugs out.
Does tapping the crankshaft have any adverse effect to the balance of the crank?
cant the plugs be removed and left out? Or will that then lead to oil starvation to the bearings?
I need to read up on that a bit.
Heading down the slope.
i have to say. My machinists has been a God send. I have other P shops in the area that are lining up as customers if this repair is successful .
I am hesitant to send it out for polishing. Just some discoloring. Your machinist should have a crankshaft belt polishing machine that he uses when the crankshaft is in the lathe. If he doesn't have a "Scotch Brite" belt...buy him one. Will sleep on it for a few days. Not looking forward to try to get this galley plugs out. This is not a job you should undertake. I send my cranks out to be drilled and tapped...and when they come back, I spend 3-4 more hours "finishing" what they start. Do you have 150 psi compressed air source? Do you have spray Carb cleaner where you live? Buy some spray carb cleaner....buy a case. Buy the long flexible spray hose that someone posted a link to. Spend 5 minutes and study the crank drilling....
Clues: Each main journal feeds one set of rod bearings. The rod bearings are NOT cross drilled to multiple main bearing journals, as it appears. There's an "X" drilling in each rod journal (2 connecting rods per rod journal....1 and 5, 2 and 6, 3 and 7, 4 and 8) that connects the oil holes for each separate rod bearing. This means you need to clean out 2 "blind passages" on each rod journal. Push in the long flexible straw. Use a thin screwdriver coming in from the other side to "turn" the tube into the "blind" passage, with the plug at the end. Clean and push and pull on the straw until nothing else comes out. Repeat, several times, until no "grey" sludge comes out. Even if you use 3 cans of cleaner on each journal, the cost will be cheap, compared to removing the plugs. Do this cleaning before polishing. After polishing....just spray the passages out one more time (There will be no thick nasty gunk for the "Scotch Brite" stuff that comes off the belt to stick to.....the passages will be clean of all gunk....any left over debris will rinse right out.
Does tapping the crankshaft have any adverse effect to the balance of the crank? No. Not enough mass change to even detect on most balancing machines...."balancing" is actually not that close of a science. (If you remove the crank from almost any machine and turn it 90 degrees, you will get slightly different readings.)
cant the plugs be removed and left out? Absolutely not. Or will that then lead to oil starvation to the bearings? Oil, which needs to "dead headed" at the plugs to force oil to the bearings would flow right out the holes....zero oil pressure at all the bearings.
I need to read up on that a bit. Not much. After looking at the crank drillings for 5 minutes and thinking about how oil gets to the rod bearings (and how you get oil pressure), you will understand this.
Heading down the slope. This is simple, everyday stuff. Relax.
i have to say. My machinists has been a God send. I have other P shops in the area that are lining up as customers if this repair is successful . See line above.This is "See Spot Run" stuff. If the local "P" shops are not busting their asses cleaning crankshafts....from any Porsche engine....................................well, they should go do something else.
03-03-2019, 04:45 PM
