Pelican Parts Forums - Bore Scoring

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Bore Scoring - possible?

From another post I have elsewhere:

Question for pro and well informed diy.
Both Porsche and BMW, a big worry is bore scoring.
Wondering if the search for improved efficiency is partly to blame.

If you could do a experience check in your head - is the scoring you are aware of mostly in automatic transmission cars?
I seem to notice, in the quick shifting to a higher gear, more engine lugging.
Engine lugging to my knowledge, causes higher cylinder pressure, among other issues.
Possibly piston instability?

If you are shifting a manual transmission, at least for me, I tend to bring revs higher than an auto would.

So the meat of the question is:
Does shifting to a higher gear, and incurring engine lugging, contributing to bore scoring?

Interesting question.

One of the recommendations for cars that may get bore scoring is to keep revs low until the oil is up to temp, but ALSO as well as low revs, also low throttle openings to keep pressure low.

The one or two times that I've driven an auto or PDK Porsche, I was surprised at how quickly it shifted. It would drive me bonkers on a daily basis. But if you're a bit heavier on the throttle, those cars rev higher so the answer is to manually shift or just be a bit heavier on the throttle.

My understanding is that the worst time for bore scoring is if the engine is cold. And it's worse if the engine is cold and the revs are also high, especially in the "S" cars since they have forged pistons.

Plus 1 on the interesting question. The only thing I can think of off hand is that with the PDK the shift is aided by a quick signal to the engine. Not sure exactly how they do it but either the spark is killed or the injectors are killed, or both, for just an instant.

That should prevent the "lugging" theory as being the problem. So IDT it's a valid question.

I'm going to agree with Steve about temps... but what I have read is that keeping the revs low all the time is more of a problem. IOW, city driven cars not able to travel much over 30 most of the time. Or just a gentle, weak driver. As my wife got older she didn't "drive" her Boxster in a way that it really wanted and needed.

I think we were lucky on the IMS bearing and cylinder issues. The only thing I can say is that I used Motul as a would be preventative. Who knows if that helped or not. And I was and still am pretty vehement about getting any car up to temp if I'm gonna drive it at all. If the distance isn't enough to get everything up to temps, I avoid the errand until I have enough to do to get it hot.

My wife's Macan will upshift into 5th or 6th at 40 MPH in normal mode. I almost always poke the Sport button and that eliminates the low RPM upshifts. On the interstate, it makes no real difference.

The engine warms up astonishingly fast. Both oil and water temps are at warm in just a few minutes.

Interesting. I wonder how advisable it is to install a low temperature thermostat to the cooling system when replacing the water pump, something I am contemplating in the future for our 2008 997. I understand it makes the engine run about 20 degrees F cooler. Does this conflict with the goal of getting to operating temperature quickly? Or two different issues (high temp on long high speed operation)? Hmmm

My understanding is that bore scoring is more of a metallurgy issue. The cylinder liners were coated with an Alusil or Nikasil insufficiently tough material that breaks down under extreme stress, such as very cold starts where there’s no lubrication in the cylinder bore. It’s why the Mezger based engines of the same era didn’t have issues, as they retain a Nikasil cylinder bore coating just like the air cooled cars. It seems the issue has been traced to cars in cold climates, which would suggest that how you operate the car is probably not a big factor.

Certainly no expert, but bore scoring became an issue at about the same time as widespread long oil change intervals and DFI. Jake or Tony C. probably have data on this.

My personal mitigation:
-Use quality synthetic oil and change it every 5-6k miles.
- Use Top Tier gas whenever possible.
-Never let a car sit and idle to warm up. Get in it and drive gently to 4000 RPM only until temps are up.
- Use sport mode often when car is warm.

I've often heard that the 996 and later cars do better if they are routinely revved higher than what is probably typical in an urban US setting.

I also wouldn't be surprised if the modern temp gauges aren't really telling us anything useful. I think they are designed to not give exact temperatures but to report that the temps are normal if they are withing a certain range. So that may explain some of the "sure warms up quickly" observations.

Quote:

Originally Posted by p911dad (Post 12539763)

I don't think running a cooler thermostat is going to impact the oil temp much.

I've run a durametric as a datalogger for my commute (84 miles each way). The water temp comes up a little faster than the oil temp. The oil temp then tends to run (in normal driving) 10-20º warmer than the water temp.

morning commute
http://forums.pelicanparts.com/uploa...1759167476.jpg

afternoon commute ~4-5 hours after arriving.
http://forums.pelicanparts.com/uploa...1759167476.jpg

In my commute, I was able to glance at the laptop screen from time to time to monitor the temps. I won't say that the two things are independent of each other, but I also don't think that they are correlated directly. For instance, a run up through the gears at high rpm has a bigger impact on the oil temp than the water temp. And if I stopped for gas, the oil temp seemed to cool off more than the water temp in the time that it took to pump gas.

Italian tuneup is therapeutic for bore scoring, go figure

Quote:

Originally Posted by onewhippedpuppy (Post 12539766)

Quote:

Originally Posted by Cajundaddy (Post 12539768)

Quote:

Originally Posted by javadog (Post 12539826)

There's a very, very in-depth 4 part video series on bore scoring that was done by the PCA with folks like Lake Speed, and the LN Eng folks and some others.

This is my synopsis of the video series.

Bore scoring happens because the piston and cylinder are both aluminum. The piston skirts of the affected motors extend below the bottom of the cylinders. The piston skirts have a patch of some ferrous coating so the piston/cylinder contact will be dissimilar metals and so ZDDP can do it's thing of coating/protecting the bore by bonding to the ferrous patch.
Because the piston skirts extend beyond the bottom of the cylinders at the bottom of the stroke, the bottom of the cylinder causes stress on the patch of ferrous coating when the piston changes direction (causing the piston to "rack" in the bore). When the ferrous coating wears off of the pistons, the fact that both the piston and bore are aluminum causes galling and the problem.

When the motors are cold, the oil isn't as good at protecting things so before you go crazy, you need to get the oil up to temp.

THe "S" cars with forged pistons are at even more of a disadvantage because the forged pistons have a different (slower) rate of expansion due to heat than the block, so in the "not fully warmed up" period, the tolerances between the piston and block are increased which means that the racking motion of the piston at the bottom of the bore is enhanced compared to normal up to temp operation.

The issue is worst when the weather is wintery. I think they said "below freezing" but it may have been "below 40" or "in the teens or colder".

The best ways to retard bore scoring are to 1) keep the revs below 3k and the throttle opening low (I think I remember reading/hearing 40%?) when the motor is completely cold and coming up to temp. And to use a good oil with ZDDP (bonds to ferrous metals only) AND Molybdenum (bonds to Aluminum). Change the oil more frequently than 10k, 15k, 20k, usually recommended is around 5k. The additives get used up out of the oil as the oil is run, so even if the base oils are OK with high miles, you will eventually lose the benefit of ZDDP, Moly, and the other additives.

3.4L piston showing the ferrous patch intact
http://forums.pelicanparts.com/uploa...1759169818.jpg

3.4L piston showing the ferrous patch exhibiting patchy wear
http://forums.pelicanparts.com/uploa...1759169818.jpg

3.4L piston showing the ferrous patch essentially gone and the piston galling.
http://forums.pelicanparts.com/uploa...1759169818.jpg

A couple of things-
When I was contemplating getting the S Cayman, the scored piston thing raised its ugly head. ((EXPENSIVE))
With the S engine, afai understand, when the skirt of the forged piston drops below the liner, it whacks it pretty hard on the return.
The non-S engine gets away with it as the pistons are softer.
All the bore score starts at the bottom.
The low viscosity oils do not help.
Also, most engines nowadays are some version of an automatic transmission, so the borescore average gets skewed .
Its not the transmission.
Its bad engineering.
Of course, Porsche has never done that B4.....

Steve’s post brings up a little of what I posit happens.
The advice is low rpm, low throttle open.

Start off cold and it hits the highest gear it can feasibly hit.
You go to speed up and now you have low speed, high throttle open.
Engine lugs on a cold engine and possibly more skirt slapping.
Then it does downshift but after a little lugging first.

Please keep it clean about skirt slapping.