I would have to agree with you on the overrev counts if they are some 'impossible' number in any overrev counters as arising from glitches, artifacts or something, but not real.

But if the overreve counts are not impossible numbers then they have to be considered real. As the tech told me and as I reported above a Tip equipped car can record overrevs in the higher ranges from going (too) fast down a hill.

My experience with the dealers I do business with is they are certainly out to make money but they do not at least with me appear to be dishonest or in any way not worthy of my business.

In fact, more than once I have been talked out of having some work done at a dealer by a dealer tech, probably the tech that would have done the work, because the tech advised me the work was not necessary.

My 1st requirement of a dealer is that it is trustworthy. If I get a clear sign a dealer (any business) is untrustworthy that's it. I'll never do business with that dealer (or any business) again. I've sold 2 pretty good cars before their time because of not being able to find a reasonably close dealer in which I could trust to work on these cars right, honestly.

If you do not have such a dealer in which you can trust I feel for you. It can really negatively affect one's enjoyment of what are in your words bloody great cars.

Sincerely,

Rockster.

Marcus has beaten me to it in replying to Rockster's post. His suggestion of a 15 minute test drive is totally and utterly wrong so do not assume all is well.

There is a danger period of 50-100 hours after a high level over-rev during which damage (usually timing chain related) can take place. There is another type of damage which happens instantly and that is where the valve head clips the piston crown. In this instance the valve doesn't seat properly and you will have low compression in one or more cylinders. This won't trigger any check lights as nothing monitors engine compression. The most common symptom would be a lumpy tickover which balances out as the revs increase. 6 cylinder engines hide a single cylinder fault far better than 4 pot engines. 8 and 12 bangers do it even better.

The "Tickety Tockety" noise referred to in his post doesn't sound overly technical. If you know what you are listening for there are sometimes tell-tale engine noises but they are quite subtle and not always present.

The suggestion of dealers using engine over rev activity to somehow con people out of their cars is a strange one. We don't put the activity on the cars that is the drivers job. Whilst we may have our views on how the data should be interpreted ultimately we are in the hands of Porsche, particularly with newer cars where owners may wish to put an official Porsche warranty on the car or where there is potentially an element of good will available in the event of a premature failure. The way Porsche react to the data has changed and evolved over a number of years. We are also bound by how you, our customers, react to such data.

We have had a system tester for some years now and "plugging the car in" has become a standard part of our evaluation process. It has to be for a number of reasons not just over rev activity, but I hope we are sensible in how we translate the information. 2 ignitions at range 4, 1 at 5 and 1 at 6 are indeed impossible and the data must have been spurious. Were that the case it should have been ignored by Porsche in my opinion and there was no need for a £700 "inspection".

The ironic thing is that whilst compression can be checked for, timing chain issues are much harder if not impossible to determine without stripping down and replacing. When a failure occurs it tends to do so suddenly and without warning during the afore-mentioned danger period.


Henry

I remember the post Marcus refers to. Snapped on the Isle of Man if I remember. The point there was that the car was serviced and warrantied by Porsche and they had not mentioned the overrev incident - which was before a previous major service - to him before. If there was a worry they should recommend the replacement of timing chains or at least an investigation. They didn't. When the car then let go they washed their hands. As a schoolmaster I am well placed to determine that that aint cricket.

To be fair Porsche give their customers a far less dulled down driving experience. They don't Nanny in the same way most manufacturers do putting in huge margins everywhere. I don't have an issue with a system built in designed to detect misuse. The only issue is when a glitch isn't recognised as such. My understanding is that Porsche were reasonably sensible in how they approached things although as previously stated it is something of a moving playing field with policy changing from time to time and may vary from dealership to dealership.

The vast majority of over rev activity we come across is valid and often owners can even tell you when it occurred if recent.

Henry

Don't understand your second sentence. Are you saying that Porsche don't put in huge margins In terms of pricing or that they build their cars closer to the limit in terms of technology? TBH I wouldn't agree with either of those propositions but, maybe I've misunderstood.

When you get a car brought to you with an over rev, what do you charge for inspection, or do you just reject the cars?

The chains do not stretch. They may break but it is do to metal fatigue, failure of a chain tensioner (material fatigue), or something else comes loose and gets between the chain and sprocket.

The primary risk to the engine from overreving comes from several areas. One is some part lets go. A rod, or rod bolt or the crank lets go.

In fact these are at risk of letting go at any time the engine is running. Yet, with all the crying about the IMSB no one ever suggests refreshing the rods/bolts and crankshaft when buying a used car and spending money to freshen it up.

Anyhow, the other is the valves float and the heads kiss the pistons. The best one can hope from this is the valve heads are just bent and none break loose. The engine will almost certainly have a misfire afterwards.

However, it is a rare engine overrev event that the valves just kiss the pistons.

Generally the valves impact the piston hard enough one or more valve heads break free of the valve stem. In this case the engine immediately makes it known by sounds and behavior that the overev had a very negative impact on the engine's health.

Now the techs tell me that overrevs do not matter if (big if) the car/engine is not in for any engine warranty work.

If the car/engine is in for a possible warranty claim, then if any serious overrevs are present the warranty claim can and almost certainly will be rejected.

If the car/engine is being considered and a warranty is contemplated or desired, one must get it in writing the current overrev counter values -- if there are any in the higher ranges which can be sued to deny a warranty claim -- that these existing overrev counts will not be cause to void the warranty.

If the car/engine is not capable of being warrantied, then the buyer can do as he thinks best.

If the engine has some run time on it after the overrevs -- the techs I talked to told me an hour is a good number which given the average speed of a car over its life is 30mph this works out to a 30 mile test drive, hence the 15 mile test ride and 15 mile test drive or of course 30 miles total.

More is better. But how much more they didn't say, and there is a law of diminishing returns. If the overevs are in the distant past that's one thing, but the engine is still at risk of something failing that has nothing to do with the overrevs just the fact the engine and its parts have a finite service life. The engine is only as good as its weakest part. Crank. Rod. Rod bolt (I know of a guy who lost his high miles 2.5l Boxster engine due to a failed rod bolt. The engine had IIRC 150K miles on it and its was tracked quite a bit.) Cam chain. Valve spring and so on.

Now the overrevs counts may suggest the car and the engine have been thrashed on the track (or even on the street) and this can be sufficient cause to reject the car simply because it was thrashed.

A pressure test (compression/leak down test) is not a reliable means to determine an engine's health. It is possible the engine won't even run yet pass a compression test/leak down test just fine.

It won't tell you if a rod or main bearing is knocking, if one or more lifters is noisy, if the VarioCam (Plus) system is not working right and a number of other things that could be wrong.

Also, even if the engine is healthy enough to run it may deliver better numbers than its true condition warrants. The engine as it cranks gets plenty of oil sprayed into the cylinders. This oil at cranking speeds acts to improve the sealing of the piston/rings and cylinder.

Only when the engine is started from cold and idled/run/driven from warm to hot and run long enough can the DME flag a weak (or even a too strong) cylinder by measuring the amount of acceleration each cylinder's firing pulse imparts to the flywheel. If this acceleration is outside of acceptable bounds the DME will turn on the CEL and record one or more misfire error codes.

Running the engine driving the car a good 30 miles in a variety of driving scenarios is the best way.

Not only can you confirm the engine runs right, sounds right, the DME can go through its readiness monitor check out (the Turbo DME I'm told does this twice per trip if the trip long enough) to confirm all critical sensor systems are working properly so when they are then used to verify the engine's overall health is good there's high confidence the engine is indeed healthy.

If one wants to spring for a compression test after the test ride/drive, if the seller is ok with having his car wrenched on in this manner, then go for it. But do not fool yourself into thinking they are infallible or in my opinion even worth the money. They are better used to identify where a sick engine may be sick, not that an engine is not sick.

Sincerely,

Rockster.

With the greatest respect to Rockster can I suggest you ignore his posts on this one. I have no doubt he is a real enthusiast but we are talking about a topic which could ultimately cost you tens of thousands of pounds if you get things wrong. So it is essential that any advice offered is based on fact not enthusiasm.

If you read previous posts within the thread you will see that valve / piston contact is already dealt with. There IS a risk of timing chain related problems after a serious over rev, and it won't necessarily be instantaneous. There is a danger window of 50-100 hours after the event. Once that has passed all will be well (with regards timing chain issues) but before then it is a brave man or woman who buys the car. Just to confirm we aren't talking about hitting the rev limiter, we are talking about going over it. Neither are we talking about a spurious single digit spike over 3 rev ranges.

The valve head detachment mentioned in Rockster's post won't need any specialist knowledge to diagnose. Anyone with a pulse will know something is seriously wrong

Henry

Chains need the slack taking up because they get longer due to accumulated wear in the links, not stretch.

It was Dazren - full details of incident here