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Why isn't the subaru forums littered with bore scoring threads then?
The 996/997 motors are more prone to scoring than other engines out there. The tapering of cylinders due to porous engine cases/cylinder walls is a porsche problem. If I was shopping for a 996/997, I'd be requesting a bore scope as part of the PPI. I didn't request that when I bought my last Honda or Subaru - don't have to. This motor costs $15k to build yourself, you want to make sure the one you get is a good one.
Why isn't the subaru forums littered with bore scoring threads then?
The 996/997 motors are more prone to scoring than other engines out there. The tapering of cylinders due to porous engine cases/cylinder walls is a porsche problem. If I was shopping for a 996/997, I'd be requesting a bore scope as part of the PPI. I didn't request that when I bought my last Honda or Subaru - don't have to. This motor costs $15k to build yourself, you want to make sure the one you get is a good one.
A couple of those subaru links talk about piston slap but no evidence of scoring. Every engine can/could experience scoring, not arguing that. Still - no where near Porsche levels though. Look at this and the 996 scoring threads. Busier than IMSB's threads. and I can build 2 500awhp Subaru motors for the price of a porsche flat 6 280whp rebuild. lol
Bore scoring happens as often on Porsche as Subarus go through head gaskets. Head gasket in a subaru is a days labor and the cost of machining the heads and new gaskets. Build a 3.6/3.8 N/A lately? The cost is sickening.
Originally Posted by Porschetech3
Being a Porsche mechanic also, I feel the need to take up for the trade a little bit. These M96 engines suffer from bore scoring more than any engine type I have ever seen in my 40 years of being a mechanic. And the symptoms are not typical of other engines that have bore scoring. Any mechanic who does not know how unique and widespread this problem is will find it hard to believe.
I saw this filthy exhaust on a 3.6 997 at my indy and thought scored bores had struck here in sunny California. Turns out it was just a bad coil pack and a cylinder was running rich. I guess the tailpipe isn't a reliable indicator.
2007 C4S, 23,000 miles. This is bore 6, bore 5 is similar and I stopped there. I have not had the car that long so I think this happened earlier in it's life. The car does not have any symptoms at this point. No sounds, no oil usage, no dirty exhaust tips, plugs very clean. The dealer says not to worry about it unless it exhibits outward symptoms but I'm not sure that is the best plan. I'll start with a DIY compression leak down test and then make a decision. Its a weekend touring car so maybe a wait and watch approach, or maybe a complete preemptive rebuild. The car is otherwise flawless, highly optioned, and fun as heck to drive so I'm not to upset about it. I figure rebuilding the engine is about the cost of depreciation on a new 4S the first year, and I'm a real fan of the 997 appearance and feel.
It doesn't look significant at this point. Interested to hear your plans for the compression test.
You are taking it admirably and I 100% agree on the economics of the rebuild. A buddy just bought a 2014 for almost half the original list price. That means the prior owner lost $80k+ in depreciation during 2yrs of his trouble-free warranty.
The car was purchased new in northern CA and then that owner moved to Colorado and had the car there for about a year, so it got a couple thousand miles in a cold weather area. The second owner brought it back to the San Francisco area and put a a couple thousand miles a year for his eight year ownership. Service history shows oil changes at Porsche dealers every 1-2 years never exceeding 5000 miles. Tires replaced at 14k miles and I can see by looking at them that the car has not been tracked since they were installed.
Keep us posted what Jake says. Lets hope it doesn't require a rebuild but on the bright side, a Raby 4.0 4S with those low miles would be a special car.
If you are in the Bay Area there are a bunch of guys in Marin and would love to meet up on our next drive.
The car was purchased new in northern CA and then that owner moved to Colorado and had the car there for about a year, so it got a couple thousand miles in a cold weather area. The second owner brought it back to the San Francisco area and put a a couple thousand miles a year for his eight year ownership. Service history shows oil changes at Porsche dealers every 1-2 years never exceeding 5000 miles. Tires replaced at 14k miles and I can see by looking at them that the car has not been tracked since they were installed.
I put a clutch in it when I bought it because I did not like the feel, the disk was 80% but the clutch plate and flywheel had been heat damaged so the clutch engagement was not smooth. I think the clutch had already been replaced once before and I would think just from poor driving technique and stop and go traffic. The rev counter has a total of 6 seconds at condition 1 plus 1 second at condition 2 and nothing in 3-6. Over 11 years that seemes pretty good. Average speed works out to 27 mph since new. The second owner was in his 60s and driving around the Bay Area traffic so I would think if anything the car was lugged too often which really loads the thrust side of the piston.
I have been doing car restoration as a hobby many years (mostly vintage Corvettes) so I do most mechanical work myself. Porsche’s are different, but still just a car when it comes to working on them. I own a aircraft grade articulating borescope so I did the inspection myself. Still, the depth of the marks in the cylinder wall is difficult to interpret since I have little experience with inspecting for scoring or follow up tear down to verify the accuracy of the interpretation. I sent a photo link to Raby to see if they would take a look, and will combine that info with the results of a compression leak down to determine if I will take any action at this time. Meantime since there are no symptoms and it runs fantastic we will continue with our usual Sunday road trips and not worry about it. I’ve gotta think that if more cars were scoped, results similar to these would be very common. I would bet 98% of these cars would never get scoped without symptoms. I only did mine because I had the equipment and a free afternoon.
A compression test won't show anything until it's far gone. I can verify the cylinder is indeed scored and eventually will cause trouble. If you want to try to validate the damage with used oil analysis, you would expect increased AL values, which should be <5 normally, and usually 1-2 in healthy engines.
Thanks for the input Charles and I agree completely. Raby also got back to me personally with a prompt and well considered response to my list of questions.
Tonight I did some interesting further investigation. I scoped the other cylinders and found varied but similar results in all cylinders in both banks 1 and 2. I started thinking about the Hartech article I read about it being very hard to tell if you are looking at polishing lines with no consequence or actual score marks with depth. The light in the camera really highlights the polished areas and will make them look like more than they are. So I decided to scope my 2013 Volvo with 36k miles and my 64 Corvette with 1k miles (since rebuild) and they looked the same with areas of vertical lines very visible in the camera. In no case on my 997, Corvette, or Volvo could I conclude that these lines have any depth. All cars, including the 997 are without symptoms. So either I have a lot of engines to rebuild or I need some more experience with the camera. 😬 The thing is, I would I guess that others may also have trouble with this, including some professionals. So at this point I fell pretty safe saying I don’t have a bore score “failure” in my 07 C4S. Time will tell.
So at this point I fell pretty safe saying I don’t have a bore score “failure” in my 07 C4S. Time will tell.
Thats amazing news and some impressive investigatory work. If you are determined you could pull the oil pan and scope from the other side as well. Pulling the pan is pretty easy and will give you a chance to inspect the oil pickup tube and sump.
01-25-2018, 04:54 PM
