CaymanPower

Hi,

Went through a lot of investigation and it turned out like this:

http://www.planet-9.com/cayman-boxst...e-caymans.html

That thread is now closed for 'biased' reasons. However, a value of 0.25mm (checked with a dial gauge) for the exhaust valve guide clearances in the Gen2 2.9L engine was presented to me without a certified document from Porsche. So, as far as I can tell this could well be a made up number. In fact, 0.25mm seems WAY too much clearance for such tiny valves.

So, I was hopping that someone here could help me with real 'unbiased' numbers for the exhaust valve guide clearances on the Gen2 2.9L engine.

I've just asked my dealer about those numbers and he said that Porsche doesn't give them. He said that when a problem exists with the valve guides Porsche simply replaces the heads.

What do you guys think? Can anyone ask his dealer for me?


Thank you!

racer

Sorry, I don't know the values you are seeking, but since the 986/996 line was introduced, Porsche has always moved to replace something rather than let a dealer/DIY person learn about the product. It took about 5-6 years before folks could start tearing down the early M96 motors vs Porsche simply exchanging them out. I imagine Porsche might have enjoyed that process and keeps it going with the new cars.

CaymanPower

Thank you racer for taking the time to answer.

Do you also think that number was made up, then?

Macster

Well, 0.25mm is 0.009". This means the clearance is 0.0045". Roughly the exhaust valve clearance wants to be quite a bit less than this maybe down to 0.001" per side or even less. I think less but I'm not sure. It has been a long time since I could recall valve stem to valve guide clearances.

But the number is within the range of believable.

Assuming the number is accurate, nine-thousandths of an inch (0.0045" per side) is alot of clearance and it is no wonder the engine smoked. I would think the engine would have been noisy too with that much valve stem to valve clearance.

I'm pretty sure one of the dealer's techs has the valve guide to valve stem clearance numbers in a reference somewhere.

(On a similar vein a while back the question of main/rod bearing clearances for the previous generation Boxster/996 engines came up and I was told by the techs I talked to not only did they have this info -- though buried under more recent info/literature or stored away in a box somewhere (the info is given out during the new model intros) -- but they had the info for the newest engines too and this was probably easier to find if I wanted it.)

But why do you care what the numbers are?

If the heads are being replaced, take the new heads and run!

Sincerely,

Macster.

CaymanPower

Macster,

0.010" on a dial gauge for the exhaust valve guide to stem clearance would be a lot on most engines. And yes, smoke at startup would be very likely.

My heads are not being replaced. In order to have my bank #1 head replaced under warranty in virtue of bad exhaust guides it would be a great advantage to have precise numbers. My dealer says Porsche doesn't give those numbers so even if he measured the clearances for me he wouldn't know what would be excessive or not. This is a very odd situation, to say the least. Nevertheless, if I presented him the real numbers, dealer is willing to pull the head off and do the measurement. So, all I need is the correct numbers and everything will be quickly sorted out.

If you think one of your dealer's techs has the valve guide to valve stem clearance numbers in a reference somewhere for the 9A1 2.9L engine, would you mind to ask him what the numbers are?

racer

Sounds like you need to find another, more friendly dealer, or get the local PCNA rep involved to determine the cause/fix of your smoking motor. A new motor shouldn't be smoking.

CaymanPower

You are absolutely right racer. Don't know why some people think otherwise just because the engine is 'flat'.

Macster

I have to agree with racer. It is not your job to tell the dealer the allowable clearances of anything in the engine.

The dealer asking you to supply these numbers to it is a classic and very obvious stall tactic. One that one would think a Porsche dealer would not even be aware of let alone stoop to using.

If you are relating the circumstances accurately, one might believe Porsche should question this dealer's acreditation. Were I Porsche I'd not be too keen on having this dealer represent Porsche.

A letter to PCNA asking if it is common for a Porsche customer to have intimate knowledge of the internal clearances/dimensions of his Porsche's engine before he can expect reasonable service from a dealer might be in order. And if so why are these not published in the document/literature that comes with the vehicle?

I do not know where you are but generally the dealer owes you reasonable skill and experience in servicing your vehicle. Remind the dealer one *major* factor in your decision to buy the car and from this particular dealer was its stressing to you as part of its sales pitch of the car its factory trained and highly experienced technicians.

If the dealer is asking you to supply internal engine clearances this is clearly a sign the dealer either can't or won't provide you with the reasonable skill and experience that you were led to believe you could expect.

This is consumer fraud.

You can do some research on consumer fraud in your area so you can at least know what the steps are, what you should do or try to do, how you should continue to interact with the dealer to adhere to the consumer fraud guidelines so you are on as firm of ground as you can be should you need to escalate this to a possible consumer fraud complaint.

I'll email a tech I know and see if he can supply me with the info you seek.

Sincerely,

Macster.

Macster

Well, I submitted your request to a tech and he responded that the request to well be blunt, sounds fishy. No dealer should require you to supply this info. Whether he will follow up with the info I asked for I do not know. (If he does I'll post the info.)

But he has a point. I do not recall the history of the situation with your car, but if the engine is smoking and the car unmolested and under warranty the dealer should look into this without any need for you quote clearances. If the dealer says the all do that, be sure to ask for a demo using cars that the dealer has on its lot or in its showroom

Sincerely,

Macster.

CaymanPower

Macster,

At this point i don't have any single evidence that Porsche makes the the exhaust valve guide to stem clearance specs, in the 9A1 2.9L engine, available for the dealers. Thus, i don't believe my dealer is lying.

So far, all i have is a number (0.01" - dial gauge) that someone threw on an internet forum, without any quote or a print from a Porsche book, just to 'shut me up' (read the link i've posted here) because he felt challenged.

Thus, unless someone here can provide that kind of information from his dealer i will assume that my dealer is telling me the truth because, as racer had put it, dealers are not instructed by Porsche to replace the valve guides. This is a job for machinists and professional engine rebuilders. Dealers will only replace the heads and only if Porsche considers them defective. Until this day, i've never heard of Porsche officially assuming a defective head in a new unmolested engine, even in the 993 era (where some 993s were notorious for very premature valve guide wear, in some cases, with only 10k miles). Dealer is not requiring me to supply this info because he doesn't expect me to have it. He keeps saying Porsche doesn't provide this information and so far I don't have any proof that they do.

Also, 0.01" is NOT believable. The exhaust valve stem-to guide clearance for most passenger (water-cooled) cars ranges from 0.002 to 0.004". They require about 0.0005 to 0.001" more clearance than the intakes for thermal expansion. Heads with sodium-filled exhaust valves, like those you will find in a STi Subaru Impreza, usually require an extra 0.001" of clearance to handle the additional heat conducted up through the valve stems. Therefore, in the worst case scenario if one considered that the 2.9L Caymans had sodium-filled exhaust valves - which they don't - the maximum allowed clearance for the exhaut guides would be 0.004" + 0.001" = 0.005". As you can see, this is half of the value that someone provided as an official Porsche number without any quote.

Who is lying, then?

Macster

As I mentioned in an earlier post I can't say exactly what the clearance should be but my educated guess (from memory of the engines that I worked on in the past) is the clearance should be much less than that 0.010" number, on the order of half or less.

That is the diameter of the internal diameter of the valve guide should be smaller by at least 0.002" and possibly double that number to provide a clearance of between 0.001" to 0.002" between the valve stem and valve guide. Too little clearance and the risk is the valve will stick from heat expansion and lack of oil. Too great and the engine can have use a lot of oil, smoke, and run noisy.

The factory problem publishes that number in some internally distributed literature. Several techs have told me this is true for the older generation engines and one who told me this is true for the new generation engines.

What Porsche probably doesn't do at this time is permit the dealerships from tearing into these new generation engines. At least to the valve stem/guide clearance level. (In some case, say a noisy lifter or even a failed valve spring, Porsche might permit the dealer to remove the camshaft cover and remove the cams and remove the bad lifter or even the whole row of lifters and replace them or remove the broken valve spring and replace it with a new one. What won't likely happen is that anything that requires precision measuring, machining, etc., will be permitted. Most auto techs aren't trained in what is commonly (or used to be anyhow) referred to as heavy duty repairs, heavy in that they involve substantial engine teardown with machining operations. Most dealers do not have the equipment and I'm sure Porsche is not keen on warrantying machine work by the local automotive machine shop. While there are good ones there can be some really bad ones.

From Porsche's point of view it is better (cheaper and delivers a better customer experience) to simply remove the old engine and replace it with a new one, one that has had any heavy duty work done on it at one facility, by properly trained, experienced, and equipped techs. At the Porsche factory.

Makes sense: It wasn't until just a few years ago that Porsche started allowing dealers to tear down and evaluate the older generation engines for suitable rebuild status in the event of, for example, a failed IMS bearing.

For these newer engines the dealer will -- assuming the engine exhibits symptoms/behavior or upon partial teardown certain conditions are found -- simply remove the engine and replace it with one sourced from the factory. The removed engine goes into the crate the new engine arrived in and the crate with the removed engine in it goes back ultimately to the factory.

If the car's engine is smoking constantly that has to be quite obviously an abnormal condition and one I think -- FWIW -- addressed by a new/replacement engine provided no other reason can be found for the smoking. That is Porsche might have a check list of things the dealer has to consider, eliminate, before the engine qualifies to be replaced.

I still don't understand your fixation on the valve clearance values though. Perhaps I'm just not seeing the link but to my mind you should not care what is wrong, but only that something is wrong, and it should be addressed under the car's new car warranty.

Sincerely,

Macster.

CaymanPower

This pretty much sums it up.


If you read the link I posted here you will understand.

Also, I had the chance to measure the exhaust valve guide to stem clearance in cyl. #3 of my engine for reference (the dial gauge has a 0.0004" (0.01mm) graduation):
http://www.youtube.com/watch?v=gxIh10CgqLw

As you can see (via a poor quality mobile phone camera film), the gauge is measuring around 10 x 0.0004" (0.01mm) = 0.004". This corresponds to the upper limit of the above mentioned exhaust guide clearance range.

Although, we are in fact dealing with 'loose' clearances there the question is: what is Porsche's factory value?

Can you help me Macster, or anyone of you?

Macster

Well, the clip was not good enough for me to tell much of anything, but I believe you if you measured 0.004". But I have to wonder what it is you measured? The useage of the measuring tool seemed wrong to me.

When I measured valve stem to valve guide clearances, I'd use an OD micrometer (good to 0.0001" resolution) to measure the valve stem diameter. I'd take enough measurements to have a good feel for the stem's diameter its entire length and that it not tapered, out of round. (Also, I'd check the valve for straightness.)

Then I'd use either a snap bore and an outside micrometer (the same one used to measure the diameter of the valve stem) or a dial bore gage (again with a resolution of 0.0001") and measure the valve guide's bore diameter, again at several points around and up and down the length to get a good feel for the quality/consistency of the bore's internal diameter. As with the valve stem, the guide may wear out of round or develop a taper.

(Also, I was taught to with the valve springs removed to hold the valve closed and wiggle the valve stem and then to allow the valve to move down in the guide and continue to wiggle the valve stem to get a feel for how much play and therefore wear there was. I do not recall the amount of play but it wasn't much and it was a guick way to determine if one or more valve stem/guide pairs had excessive clearance.)

In my measuring I never found anything amiss but since I was sending the head or heads out anyway for a 'rebuild' I'd just have new guides (and seals) installed and the guide inner diameters sized to provide the proper clearance for the valve stems. Also, I never found any valves that needed replacement. But they would have their working faces touched up to freshen up the seal with new valve seats in the 'rebuilt' head(s).

I will see if I can get the info you seek. The tech I contacted the other day did not respond with the info. He didn't say it was not available, or that he would not supply it. It may be that he may be too busy and the info buried too deep.

He's been real generous with info that he can put his hands on but this is the first request I've made for what I suspect is info buried in some literature he received some time ago when the 2nd generation 2.9l engine was introduced.

Sincerely,

Macster.

CaymanPower

Thank you very much Macster! The value that Planet-9 gave me for the dial gauge test is a 'dummy' number (0.01" is WAY too much), that i'm sure of because i already had done the test to cyl. #3 and #2. However, that's not what i'm interested in. All i care is having the correct exhaust valve guide to stem clearance value and its tolerance. Oddly enough, the dealer mounted the head on the block without me asking and before i could check cyl. #1 which is, precisely, the suspected cylinder. With the correct numbers as a reference everything can be quickly sorted out.

CaymanPower

The measurement was taken using a dial gauge with a magnetic base like in the following example:


and with 0.01mm of resolution: