phil@tech9

Ok guy's,

I'll start a new thread, and try and offer my experience to date with the 993 valve guide wear.

We have found that any cars (including Turbo's) that have been subjected to track days, and city congestion have accelerated exhaust valve guide wear.

I have not had to replace any inlet guides on engines that have been subjected to the above.

My theory, is that Porsche switched the valve stem size on the 993 models to 8mm from the earlier 9mm. I would observe that this will lead to hotter temperatures of the guide itself, and due to the increase of friction between the valve and the guide, lead to accelerated wear.

It has been discussed at great length on this site regarding the undertray, It is my opinion that this is a major factor that contributes to this problem.

My views and comments are based upon my experience here in the UK, and having been involved in a large number of engine rebuilds on all 993 models.

Kevin

Phil;

Can you give us some stats, how many miles, what year the cars are, and how many have you done? TIA

Pete @ Andial

We have done 19 993tt with the lowest at 8100 miles and highest 37.000 miles. Seven of those engines needed intake guides also.
Pete.

tom97c4s

Does this mean that if I take off the engine undertray I can avoid this problem, or least substantially delay it?

TIA

Tom

Steve Weiner-Rennsport Systems

Hi Tom:

I'm sorry to tell you that its very tough to avoid the problem although removing the engine undertray does help and we do recommend it.

Our experiences with the 3.6 litre (and 3.2) engines echoes Pete's.

The primary cause is the valve guide material used by Porsche. The secondary cause is a QC issue with how the guides are fitted to the valves and internally finished. To me, they appear to be 'reamed-to-fit', not honed. Some time back, I rented a fiber-optic borescope and took a closer look at the surface finish inside the guides. Not too good but certainly what you'd expect to see when building engines on a production basis. I've alsos see ncases where the guides were not installed straight and the valve was not centered on the seat. Needless to say, this does not promote an effective gas seal and helps account for the differences and variances observed in 3.6 engine power output.

When we do a valve job and install new guides, they are always hand-honed, never reamed to fit the valve stems. Same principle for valve seats. These are machined with carbide cutters, never ground with stones to achieve a much smoother surface finish and better, longer-lasting gas seal. These are procedures that really cannot be practically done on a production line.

MarkC

Is there a possible compromise where the undertray can be modified to allow better cooling and still offer protection of the most vulnerable parts of the engine.
I would imagine cutting large holes or whole sections out close to the heads but leaving the centre section under the crankcase untouched. Of course this could make the undertray too flexible to be of any use. Anyone tried it?

Francesco

Phil / others

are these engine quite "tappety" normally? I find that when you drive past a wall for instance with the window wound down and a trailing throttle, one can hear tappet noise quite clearly? Just wondering??

I thought these cars were meant to be Bullet-Proof??????

phil@tech9

Francesco,

It would probably be a good idea, to have your Porsche technician have a listen to your engine, to decide whether or not you have noisy hydraulic tappets. It can be quite common for these cars to suffer tappet failiure.

Is it worse from cold, or is it constant ?

phil@tech9

Kevin,

In response to your question regarding particular engines, models and years. It is no specific mileage or model/year, but a general finding, when we open these engines up. As I stated earlier probably the newest was a '97 model with 27,000 miles.

The majority of the cars that we have repaired, has been a consequence of finding the wear when carrying out camshaft upgrade or capacity increases.

I calculate that we have replaced the guides on 5 993TT, and 11 993(272/285)

Francesco

Phil

maybe you'll be the Technician doing the listening !!! It's constant but not terribly noticeable. As I said, it's only when the sound rebounds off a wall. This board is giving me sleepless nights!!
Roughly, what's the cost of doing the exhaust end tappets on a 993?

regards

Rob O'Meara

Francesco, get your car checked out. This sounds exactly like my car's condition. If the failing tappet / valve guide is on the exhaust side , I need a wall or similar to hear tapping from the driver's seat. If your car has no corrosion or complications it should only take 3 or 4 hours to change the upper bank of exhaust side tappets. The job can be done with the engine in place. You'll also need to budget for a full oil change and gaskets.

Regards

911-TOUR

I think this is getting a little out of hand. Every 911 I have ever driven exhibited some valve-train noise when the sound was reverberating off a wall. Does anyone else still do the throttle check when checking the oil dipstick ?? Every time I fill up, I check the oil level with the car hot and level, and then check the throttle response by tapping the throttle assembly. I then bring the engine up to 6000 RPM slowly, listening for any odd sounds. If the valve train were making excessive noise, you'd surely hear it somewhere between 1000-6000 RPM.

Some amount of wear is always going to be present in an engine, it's the nature of the beast. If you look closely enough, you'll find wear on a Honda's valve guides at 10K miles. If your car exhibits normal compression, and isn't consuming quarts of oil for breakfast, RELAX !!! It'll be okay. If it does have these symptoms, by all means have it looked at. But there's no use in spending $$ for something that may well be a design factor for the engine.

Are there any Porsche engineers in the house ??

Okay, I'm off the soap box now.

cheers,

sean

phil@tech9

Francesco,

You would normally try and isolate one bank of cylinders, and replace all the tappets from one bank.

For reference, I would charge around £480 inc. VAT to replace the whole engine set.

Francesco

Rob
I thought your car was making unbelievably loud noises?

As for our colleagues suggestion of us all panicking; I'm not. I'm merely trying to gleen some knowledge off others on the board. Being my first 911, I have nothing to compare it to. I don't think it's anything untoward, but just checking.

cheers

Rob O'Meara

My tappet / valve train noises on my car used to be reasonably subdued, in fact I naively bought the car in this state. The Porsche main dealer (yes) told me that tappet noise was normal for turbos (the car had 38k on the clock). My previous Carrera 4 did not exhibit this characteristic. I realise now that I had been lied to. The noise just got progressively worse until I had to shell out a load of money to get it fixed. Serves me right for listening to the Porsche mechanics - I should have commissioned an independent assessment.