leebusmag100

Hello all. My first post here for some opinions. Appologies for the long post.

I purchased an 07 997 turbo basalt black 14k miles coupe from a main Porsche dealer in the UK. This was 6 weeks ago, the car is under warranty. After a few days I noticed a slight rattling that could be heard when the revs are between 1400 - 2000rpm ie just enough throttle to keep the car moving. When I say slight, if the air conditioning is blowing or the radio on fairly low you cannot really hear it. You can hear it from outside the car though.

So, phoned up the main Porsche dealer in Hatfield car was looked at by one of their top mechanics. He said, its normal, its a characteristic of the engine, they are a gt1 derived engine and do get a bit of gear noise from the rear of the engine as gear meets gear instead of belts. The sound kinda got under my skin and I ended up with the air con off and radio off just listening to it! a bit obsessive I know.

Again, 1 week later, spoke to Porsche Hatfield who arranged for their master mechanic to take a look. Again, same explanation, said they aren't as quiet as the normally aspirated engines and that the bulk of the engine is fairly primative. Said that when I am slowly accelerating the gears between the IMS and crank thrash a bit. Some are noisier than others, this one is not that noisy he said and is normal.

Still concerned I drove to another Porsche main dealer in the UK unrealated to the Hatfield dealer. They said, dont worry about it, it is normal. When they listened to the sound to start with it took a bit for them to realise what I was actually going on about.

Ok, another few days later. Phoned Hatfield main dealer, moaned saying the noise is irritating they said ok bring it in. Took it back, they gave me a brand new boxster hire car. They said that their engineers are saying there is no problem with the engine whatsoever and that they are sending my car to Porsche Reading, the Porsche UK head office to get another opinion. The car was gone 10 days. The top guys in the UK tested the car fully and reported that the car was normal, everything within tolerances, said if they thought there was a problem they'd repair it under warranty.

You can probably all tell by now I have possibly gone over the top, but I just believe that the car should be quiet.

Still annoyed I met with the Hatfield director and a few from his team. Said I cant believe it should sound like that, didn't hear it in my 997 4s cab. After pushing for 1/2 hr they said if they take the engine appart check everything and put it back together and it still makes the same sound 'as it is a characteristic' will I be happy. I said providing they check yes. They said they would check bearing tolerances etc. So, without my car for another 13 days. They called when they had seperated the gearbox from the engine and said they think they believe the flywheel isn't springing back properly and that the clutch could do with replacing. They said this would likely quiet things down a bit as the flywheel might not be damping properly. Meanwhile, I went out in another turbo and could make out the same sort of sound but not as pronounced.

Got the car back, not really any improvement, Porsche are pretty much saying the car is NORMAL you need to understand it is a race engine etc etc.

So I decided to put my radio back on and forget it. But then I didn't have my radio on one day and I could make out the same noise, not loud, just there.

I took the car to an independent Porsche specialist for an unbiased opinion. The technical director listened to the car and said that they do do that quite often and that its just a bit of play between gears. Dont worry about it the engine is fine. I said If I were to trade the car in to you would that noise effect the value. He said no, its a small noise.

So guys what do you make of all this, am I being OTT?

LlBr

Hummm..., I know the feeling. OTOH, the experts all say, "Normal," so what are you going to do? Have a seance and ask Dr. Porsche?

One truism I go by is: Porsche engines sound like a bucket of bolts about to spill over when at idle. IOW, they sound very unflattering when just sitting there running.

Anybody want to argue against that "truism?"

Plus: I think it's accurate to say, because of the way they are manufactured and assembled all engines are slightly different. For example, some burn waaaay more oil than others and are considered "normal." Therefore some would be slightly noisier too? Relax and try to forgetabout it!

BTW! You DID get those turbos lubed didn't you? That was the subject of a 2007 MY recall a while ago.

leebusmag100

Thanks for that. I suspected that was the case after all the normals!!
Not heard anything about the 07 turbo lube? Mine is an 11/07 just missed the 08 boat.

LlBr

Yes! Turbos need a squirt of lube. Not sure which model years are effected, but my usa-sold 2007 got the turbos lubed last time I took it in.

I wish I were more resourceful and could provide a link to you.

Nevertheless, I'm sure it's easy to learn about somewhere in these forums.

leebusmag100

Ok will have a look. Thank you for the advice. So re: the noise. I really should just learn to live with it.?
I also thought that there was a small amount of oil in with the turbos?

Macster

Without being able to hear the noise it is hard to say that you are being OTT or there is a problem.

I believe with all the people who've looked at the car, listened to it, that if the noise were suggestive of a real problem it would have received attention.

I hope this doesn't come across that I'm unsympathetic to your plight. I'm not.

In an effort to help allay your concerns:

Due to a various factors, normal manufacturing tolerances I believe based on my background in manufacturing is the the primary factor, engines/drivetrains vary in the amount of noise they generate, normally generate.

Bring two otherwise identical cars side by side and one will be quieter or noisier than the other. Maybe not by much but maybe a lot.

The Turbo engine has a gear driven layshaft (not a chain driven intermediate shaft the M96/M97 engines have), driven by a gear on the crankshaft.

Gear drives, all other things being equal, are noiser than chain drives. More efficient, sometimes simpler, but noisier.

The Turbo engine is a highly tuned engine. This means that at idle it will not idle as smoothly as well a lesser car's engine.

This variation in idle speed means the crankshaft's rotational speed varies slightly every firing pulse. This translates into gear rattle cause the driving gear on the crankshaft speeds up a bit upon a strong firing pulse and loses speed from a less strong firing pulse. The flywheel/vibration dampener help to well dampen this but are not always successful.

The noise you hear is the lack of 100% success in controlling/dampening this variation in idle speed from firing pulse to firing pulse.

As an aside: Were it to become too great a variation the engine controller would set the check engine light on and log a misfire error code, cause the engine controller constantly measures the acceleration or lack of it imparted to the flywheel every firing pulse and if it detects too much variation, too mjuch over a span of time, a misfire error is flagged.

Oh, with engine idling and the car stationary another source of rattle can be the clutch friction disc rattling a bit on the input shaft splines or the input shaft and its gear sets rattling inside the transmission with the gear sets the input shaft gears sets enage. Any high frequency variation in rotational speed and there is as I touched upon above will almost certainly result in some rattle like noise. One way to see if this is possibly accounting for some of the noise is to press in on the clutch pedal. If the noise goes away then what you were hearing was clutch disc with some transmission gear rattle.

Now even underway at low speeds and low engine rpms there's still some variation in the firing pulses and there can still be some rattle. There can be under some conditons some harsher noises sometimes arising from drivetrain clearances. An example is sometimes when moves the car off from a standstill either forward or backwards he'll hear a clunk. This is normal drive train clearance.

Not until engine speed increases, load increases and other noises help drown out will this rattling noise diminish.

Absent a more definite sign of trouble what you can do is several things:

1) Be sure you have/save paperwork that shows you took the car in for the noise complaint and this paperwork clearly identifies the car, its correct mileage at the time, and of course contains a description of your complaint.

2) Allow the engine to warm up a bit before driving off. With my 03 Turbo I wait until the idle speed drops from its elevated cold idle speed down to near its normal hot idle speed. This takes less than a minute in most cases. As the engne idles you can hear a roughness to its idle and as the idle speed descreases there should be a marked improvement in the engine's idle: It gets smoother.

3) Avoid low rpm low speed driving. That is running the car at near walking speed in 1st gear. This will cut down on the noise generated. I mean if you have to drive the car this way due to various reasons you have to. I'm not suggesting you blast through parking lots at highe speeds to avoid some engine/drivetrain noise but I think you'll be happier if you train yourself to avoid subjecting the car and engine to operating conditions that manifest the noise.

In number (3) above, use the lowest gear possible to run the engine at the highest speed possible and yet of course maintain or stay at the speed you deem appropriate, necessary, and safe under the conditions you find yourself driving.

And lastly, keep an eye and ear out for any incease in symptom severity or any new symptoms.

Monitor vital fluid levels too. A new car is generally a problem free car but a new car can develop problems and you want to note these as soon as you can and while noise and other more obvious symptoms generally appear sometimes a vital fluid level changing drastically is an early warning sign.

Sincerely,

Macster.

leebusmag100

What an excellent reply. I am so appreciative of your comprehensive response. Some of what you have said including the cylinder firing and crankshaft movements has been said to me by Porsche engineers so I am starting to believe I may have been a bit ott.
I have everything on emails and recorded in case there is ever a future problem. Guess I'll just get on and start enjoying it.

thanks again.

leebusmag100

One more point, the noise is more pronounced when the engine is warmed up. I guess thinner oil, expanded gear clearenaces?

LlBr

Yeah, Macster! Here's to you, AGAIN!

leebusmag100

Hey LlBr, I am also very appreciative of your response.
After these responses I've just been out in my car and given it a good run around the UK country lanes...no police, most I've enjoyed it since I got it.

911/Q45

Turbos also have an extra oil scavenge pump that the NA engines don't have and it can rattle a bit at idle.

leebusmag100

Good point thanks for your input. The idle isn't so bad, its more the 1400-2000rpm when there is some load on the engine.

thanks again

Macster

The increase in noise can be due to thinner oil. This bit of info raises several guestions. 1) When was the oil last changed? 2) Was the proper oil used?

Too many owners -- and through no fault of their own other than relying upon in my opinion (and I'm not alone in this) much too extended oil/filter service intervals -- leave the engine oil in the engine too long. Now a new engine is particularly prone to the contaminating its oil with unburned gasoline and water. This is natural for a new engine to do and in fact to a lesser extent any engine to do.

The only way to deal with this is to change the engine oil/filter as soon as this level of contamination reaches some unacceptable threshold.

Now one way to know when to change the oil is to run an analysis of the oil.

This has its pluses and minuses, which I won't cover.

Another way is to just pick a reasonable mileage number and change the oil. For a car with a new engine I like an oil/filter change around or even a bit before 1000 miles, and another at 2000 miles (1000 miles later) at the end of "break in".

Then another oil change 3000 miles later, at 5000 miles, and then every 5K miles for as one owns the car.

I followed a schedule similar to the one above with my 02 Boxster and it has over 231K miles on its original engine and the engine runs as good today as it did when I first brought the car home from the dealer.

Anyhow, if it hasn't been changed in a while, say 5K miles, or if the wrong oil was used, it might be worthwhile (very worthwhile in fact required if the wrong oil was used) to change the oil and see if fresh oil reduces the noise.

I will add temperature affects cars in strange ways. Cars are just noiser in colder weather. Sound carries better in a cold car and in cooler air. This is true even if the engine/drivetrain up to operating temperature.

Clearances are funny things too. Heat up a block of metal a block with a hole in it, a relatively small hole in relationship to the size of the block, and the hole's diameter gets smaller before it gets larger.

Components that depend upon the castings or fabrications in which they are assembled for their positional relationships with their mating components can gain some additional clearance between their related components, theoretically.

Transmission and engine castings expand when hot. So of course do heads and camshaft platforms.

In the transmission the various parallel shafts grow apart as the tranmission cases heat up but the gears swell/expand from the heat as they heat up so dimensions between the various mating gear sets stay rather relative.

In the case of the camshafts, as the aluminum in which the camshaft is held and in which it rotates heats up this works to increase the clearance between the cam lobes and the valve lifters. Now the lifters have zero valve lash feature which compensates for this to some extent but these lifters are also fed ever increasingly warmer engine oil which of course heats these components so they grow dimensionally (in all directions) and the same relative clearances are maintained with the bore the lifter resides in and with components (cam lobe mainly) it of course interfaces with.

Generally a noise that worsens when the engine is hot is related to oil supply or oil pressure. But this doesn't mean every noise is. Another source of a noise that can get worse as the engine heats up is an exhaust leak. Another is a loose or even cracked/defective spark plug. There are of course more possible sources of noises. To complicate things, many of these noise sources can be noisy when the engine is cold and can quiet down as the engine heats up.

Sincerely,

Macster.

leebusmag100

Excellent reply again, so informative.
Ok, the oil has just been changed 2 days ago with Porsches recommended mobil 1 oil 0w40. Before this I had tried a thicker oil castrol edge 10w60 which made no difference. The noise is definitely coming from the rear of the engine and fits in with your previous post/description. The service book also states the car had its oil replaced in October 2009, 2000 miles ago, so it has had plenty of changes. I have the necessary knowledge and tools to change the oil myself so will replace every 5000 miles.

Regarding heat and metal expansion. It was explained to me that the main engine case (excuse my poor terminology) expands when engine is up to temp moving the crankshaft gear and ims gear apart ever so slightly which gives a greater clearance and the rattle. So it looks like everything you are saying is tying in with eveything I have been told.

Very much appreciated.

Macster

Regarding the oil I believe the engine has received excellent attention in this area. My hat is off to you.

The engine cases do expand as the engine warms up. If one were to measure the distance between the crankshaft center line and the center of the two exhaust camshafts when the engine was cold then up to operating temperature I would expect to see the distances greater when the engine was hot.

Aluminum's coefficient of expansion is 0.0000123 inches/per inch per degree F.

(I might add by way of comparision cast iron's is 0.0000059 inches and steel is 0.0000073 inches. And this assumes no alloying that is intended to modify this expansion amount.)

IOWs, an inch long piece of aluminum at 72F would be 1.0000123 inches long at 73F.

The same piece in cast iron would be 1.0000059 inches long and the same piece in steel would be 1.0000073 inches long. Roughly cast iron and steel expand half as much as does aluminum.

Back to aluminum: That's not much. If the crankcase was at 72F when the engine was started and obtained a temperature of say 172F that's 100F degs. times 0.0000123 or 0.00123 inches. Just a fraction over a thousandths of an inch.

Ok but the crankshaft and IMS are not just one inch apart but more like 6 inches. So the distance between them is now 6 plus 6 times 0.00012 or 6.007 of an inch. Seven thousands of an inch is about twice the thickness of a human's hair.

However the engine cases do not heat up and the other components remain cold. Everything in the engine pretty much heats up together. Sure, the components in or at the combustion chamber heat up quicker and of course run hotter but everything in the engine crankcase proper pretty much accumulates heat at the same rate. Thus while the crankcases are growing in size from heat so too are all the other components inside the crankcase.

Thus the growth from heat the two gear wheels experienced reduces somewhat the effect of the approx. 0.007 of an inch the distance between the crankshaft and the IMS increased.

Now the camshaft centerlines are further away from the crankshaft centerline but these are chain driven (the chain even expands and becomes longer) but the chains are of course properly tensioned by chain tensioners so this extra length is not a problem.

Back to the crankshaft and the IMS: The distance between these two grows as well as the engine heats up.

They are located rather close together so they don't grow apart by much. How much is the distance between them and the temperature they obtain.

But the gears grow in diameter too as they get hot. If you could measure each gear's pitch diameter cold and then hot you'd see there was a difference: Tthe pitch diameter cold would be smaller than the pitch diameter hot.

The crankcase that holds the crank and the IMS is of course made out of aluminum and the gear on the crank is steel, at least I think it is.

Another sidetrack: Sometimes automakers use a sintered metal (steel or iron alloy) to make the gear wheel or even a non-ferrous metal. For instance the crankshaft gear wheel might be cast iron and the one on the IMS could be a hard bronze or even aluminum. To complicate matters even more many times the gear wheels are alloyed to minimize their growth from heat (along with providing them other desirable characsteristics or minimizing undesirable characteristics).

Anyhow, even if both the crank and IMS gear wheels are steel they'll expand with heat but generally not as much as the aluminum.

And another complication: I must point out that while the engine block is aluminum almost invariably it is a special aluminum alloy that is specially formulated and designed (metallurgically speaking) to not expand as much as the same casting if it were made from a more run of the mill castable aluminum so the crankcase housing does not expand as much as one might think. As a result the crankshaft centerline and the IMS centerline are not that much further apart when the engine is up to operating temperature. And the steel or whatever material gear wheels are not as loose as one might think.

One more side track: It could be one reason the M96/M97 engine designers went with a chain driven IMS so they could use a cheaper casting aluminum alloy one that would grow more with heat and yet with chain drive from the crankshaft to the IMS this growth would not result in anything the chain drive tensioner couldn't handle.

Ok, back on track: This doesn't mean though the gear wheels don't develop more clearance when the engine gets hot. They have to it is their nature. But the engine designers had to take this into account (or we'd know it from all the engine troubles being reported).

And yet your engine I'm sure still makes the noise. But I believe there is agreement while it is noticable and probably a bit louder or at least more obvious than that produced by some other examples of the same car, it is normal.

Sincerely,

Macster.