911Finally

I know the subject has been beaten to death and I did do a lot of searching but couldn't find an answer to my question. Is there any data, or opinions (could be opening a can of worms) on bore score for 997.1 S Tiptronic? I understand over revving and winding out the gears on a manual, but with the tip you're not exceeding 3500 rpm's that often especially if you're not using the paddles. I would think the incidence of bore score have got to be rather low.

voiceprint1

Ericson38

I don't think it is piston velocity in the bore that scores them. Rather, very high side loads are developed in low RPM heavy footed driving, as a matter of engine operation, which comes with the reciprocating arrangement.

This in turn results in high PSI (or other unit of measure) values (at the contact patch) due to these side forces combined with lower contact areas arising from short skirted pistons which allow for longer strokes for a given block deck height.

Hella-Buggin'

I though you gave the car back?

911Finally

Huh? You may have me confused with someone else.

Chris(MA)

If you want to know more about bore scoring, try googling Hartech in the UK. I believe they have lots of info about it?

Lots of opinions around as to what causes it, but I've heard its related to the tight clearances between the cylinder bore and piston skirt; if the piston skirt heats up faster than a 'normal' warm up, then it expands more relative to the expanding cylinder bore (which is designed to have a near exact expansion rate).
This can cause contact of the piston to cylinder wall, wearing the low friction coating off, once the coating is gone there is AL to AL contact, the silicon particles from the bore can then become dislodged and act as abrasive which scores up the piston and bore.

This explains why more cold weather cars in NE states suffer more incidences, the beginning of the failure is related to temperature and might be folks leaving their cars idling in the driveway in very cold temps, meaning the piston skirt heats up when the block is still really cold.

Tip or manual makes little difference AFAIK

Hella-Buggin'

Sorry, there was a guy last week with "911" starting his Username, who was asking about a tip w/ bore scoring.

Ericson38

Its not tight clearances (.001-.0015 is typical of even Harley Davidson air cooled engines for piston-wall clearances). But differential expansion could do it. I still don't think that is the issue either, as that one can be solved long before mass production.

cosm3os

Drive it and stay off the interwebz

911Finally

OK, I understand people want to post for the sake of posting something. I do drive it, I'm not worried, I'm not interested in the mechanics behind it and I'm not looking to spend hours researching it. All I wanted to know if there was any data showing
an equal or lesser chance of bore scoring on a tip than a manual since most seem to believe that keeping the RPM's under 3000 till warm up and the tip doesn't wind out the gears like a manual. That's all.

Racetwin2

Hartech has a very good article on their website. I am a mechanical engineer and I must say what they write makes sense.

What they say: The engine design is a bit faulty so the hottest point (cylinder 6) has the worst cooling of all cylinders. What is even more unfortunate is that the pressure side of the piston/cylinder (where the piston is pushed against one of the cylider walls) is where cooling is the worst. This is not the case for the other cylinders. That's their theory why it usually happens to cylinder 6.

To prevent this there are several things they recommend which is common sense really:
-Don't rev when engine oil is cold. Not enough if water temp is ok.
-Before revving the first time build up momentum gradually so thermostat has time to open before flooring it.
-Don't push engine on low rpm (torque is so high and engine will generate heat and coolant flow is low) same issue with pressure on cylinder wall
-Change oil and filter more often than service interval recommends. I do it myself twice per year or roughly every 5.000 km
-You can also change to a colder thermostat that will open earlier.

I suspect many engines have been revved before reaching correct temperature and that this is one of the main reasons. After all it takes almost 15 minutes to warm it up even in a summer day.



Read the full article. It's long but very interesting.

cvtbenhogan

Great points.

As for the low rpm, i think they meant general low rpm usage and any lugging of the engine. Tiptronics tend to suffer more too as the trany seeks higher gears for better economy.

Racetwin2

I agree - I always react when I hear the tiptronic as it is very low rpm before gear change. Hartech also mention that the engine is on the limit of power outtake. It was not long ago when it was 3,6 and 300 hp. Now also with varable intake the torque is much bigger on low rpm.

Bruce In Philly

I am always amazed how most folks get into their snow covered cars at my local train station and have whatever car they have in gear within a millisecond of starting.... and they just GO. The brand of car does not matter. They want to get warm and get home.

(full disclosure: this is a post to just post something)

Peace
Bruce in Philly

too tall

I've been reading Rennlist and 6speed for 5 years. No, I have never seen data saying one was more vulnerable than the other.