944 S2 Valve Spring Inspection - My Discussion w/Gemini

[Latitude48]

I've been having a disussiion with Google Gemini regarding the engine in my 16V S2. Specifically, I asked if I should be concerned about potential valve spring breakage since my engine has 155,000 miles and I recently saw a video about an S2 engine that dropped a valve due to broken valve springs. Not a pretty picture! I told Gemini that I had the tooling to pull the cams and was considering inspecting the springs.

Gemini said there wasn' an exact "time-bomb" mileage where the springs are guaranteed to fail but the general consensus among well-known Porsche specialists is failure of the inner valve springs typically begin to crop up in the 120,000-140,000 mile range. The risk is the inner spring handles a significant amount of the valvetrain load and when it breaks it can cause the valve to float at higher rpm, or in a worst case scenario, allow the valve to drop, leading to catastrophic piston to valve contact.

"While You're in There" dilemma: given the labor to inspect the springs and knowing the mileage, Gemini said to consider proactively replacing the springs, which can be done with the cylinder head on. The AI also asked about the status of the timing chain, which in my case is original (I have a new one, and new lifters too). Failure of the chain is just as bad as dropping a valve. I told the AI that my S2 does not get driven regularly. It can sit for a month or more sometimes, especially during the "dark ages" in Seattle. This in itself is not a good thing because the valve springs can experience static fatigue if the engine rests with certain valves fully open for extended periods.

Of course, another "while you'r in there" would be to change the valve stem seals. I then asked about the guides. Gemini said if the guides are worn, which they probably are to some extent, the valves can wobble and more quickly wear out new valve stem seals.

The AI then asked if the head gasket was original, which it is. It said the fact that I have a factory-original head gasket that's 36 years old and has experienced some track days (20 years ago... I've had the car for 29), means the head gasket could be a bigger ticking time bomb than the valve springs. It said head gaskets degrade from heat cycling and time just as much as mileage. The composite material breaks down, and the sealing rings around the coolant passages become brittle.

Pulling the head to replace the gasket means the top end would get a complete refresh and should be good for another few decades.

The engine in my S2 runs as good as it did 29 years ago and uses next to no oil between changes. However, I know the cam chain is old and should be replaced, and I know the valve springs can be an issue with the 16V S2, so I'm kinda leaning towards pulling the head and doing a complete refresh as i'd like to hand this car down to one of my sons or grandsons (or granddaughters if so inclined, ha, ha).

The engine is really the only thing that hasn't been updated in the last 29 years. Any thoughts from the engine experts in the group would be appreciated. For instance, are there other options than Porsche valve springs? Would you pull the head or let "sleeping dogs lie?" Thanks in advance.

[Bergerac]

I would definately do the timing chain/pads if theyre original. Its not as big a job as people make out, we replaced my 968 tensioner in a half a day. This is the thing that will cost you a head and possibly a couple of rods/pistons if it goes wrong.

Im not sure Ive heard of valve springs failing, you will know when the guides go because of the smoke on startup.

The headgasket is a hard one, I honestly wouldnt pull the head unless I had too.

[Latitude48]

I would definately do the timing chain/pads if theyre original.

The cam chain is original. The chain adjuster has been replaced twice. The last time was about 15K miles ago.

Its not as big a job as people make out, we replaced my 968 tensioner in a half a day.

You can replace the chain adjuster on a 944 S2 in an hour if you work quickly. However, pulling the cams and replacing the chain is quite a bit more involved. If you did that in half a day I'm impressed... but I work slow and methodical, ha, ha.

Im not sure Ive heard of valve springs failing, you will know when the guides go because of the smoke on startup.

The headgasket is a hard one, I honestly wouldnt pull the head unless I had too.

If you search online you'll find cases of failed valve springs. Not all result in catastrophic failure if you catch them early. I do think I get a bit of smoke on start-up if my S2 has been sitting for a few weeks. I'll check the next time as it's going to sit for awhile while the speedo odometer gear gets fixed. Thanks for the input.

[Thom]

Please delete.

[walfreyydo]

At 155k miles and the age of these cars, if you are concerned about valve spring failure, then you should just refurbish the entire head. The following is what I have done on my own car and what I would recommend:

Before removal of the head, run a compression and leak down test for baseline reference

-Valves inspected and measured against factory wear tolerance, replace if needed
-Valve guides inspected and measured against factory wear tolerance, replace if needed
-Valve springs inspected and measured against factory wear tolerance, replace if needed
-Valve spring shims measured and installed
-Hydraulic lifters and journals inspected for wear, cleaned and replaced/rebuilt if needed
-Cam lobes and journals checked for wear, polish if needed


-Valve seals replaced
-Valve faces re-ground, valve seats re-cut to match, final lap and sealing check

-Front cam seal and the three other cam plugs replaced
-Oil check valve inspected, o-rings replaced as needed
-Exhaust studs replaced
-Head measured for warpage and resurfacing
-Head measured after resurfacing for needed head gasket thickness

-Cam chain tensioner and oil feed tube inspected, o-rings and crush washers replaced
-Cam chain replaced
-Cam chain tensioner pads replaced

Other business:
-inspect cylinder bores for wear or scoring
-measure cylinder bores for ovaling, compare against factory tolerance specs
-deck measured for warpage and cleaned/resurfaced as needed
-Port and polish of intake ports, port matching of intake (optional)
-most heads will have corrosion where the head meets the cooling jackets. I have read that as long as it doesnt impact the firing ring, you should be fine. I took a safe approach and had mine ground and welded before taking it to the machine shop, even though it did not impact the firing ring. Maybe overkill on that but I wanted to completely smooth surface on my head.
-dont forget once the head is disassembled, youll have to re-dial in the camshafts. Jurgen has some great videos on how to do this (and other S2 work) here on his youtube channel. The factory FSM has a very clear process as well, so use both resources together.


Also the machine shop should be the one to do alot of the measurements and should have all the needed specifications and tools to do it properly. I took mine to a local guy that mainly works on domestics, but had done a lot of porsche work in the past, including 944s so that was a bonus.

I just went through the above process with my 968 head. I had bad exhaust guides, but my intake guides were ok. Everything else came together well, except that it was more complicated than the S2 head due to variocam.

Here is an example of the corrosion that seems common on these heads (this example is a 968 head I bought online which was already resurfaced with minor pitting compared to others I have seen):


after grinding and welding, before taking to machine shop for work:

[Latitude48]

Thank you so much for the reply and images. I had a long, long back and forth chat with ChatGPT about this to get another perspective. ChatGPT is amazing... it's just like talking to another car enthusiast. I got a kick out of some of the comments as we chatted a lot about the S2 and the 951 and what to do with them in the long run.

As you suggested, ChatGPT highly recommended doing a leakdown test to determine the state of the head. Contrary to Gemini, it said the fact I had a 36 year old head gasket without any evidence of failure was a good thing and many experts recommend leaving things like that alone if still working. The cam chain does need to be replaced and all the springs, etc. need to be inspected, which isn't exactly easy to determine their condition given the limited space. I do have a new set of lifters and I could go ahead and change all the springs with the head on the car if I got the correct tools.

Although there are aftermarket valve springs I've read that the Porsche springs are the best. I'll probably just buy a whole set now since they are available, and sooner or later the head will come off for refreshening. The AI said removing the exhaust nuts can be an issue and I responded and thought the head could be pulled with the manifold attached, which it confirmed, but said it would be heavy and to be very careful.

More to come, but thank you so much for your insights on your experience. Cheers.

[Bergerac]

I think youll struggle to get the head all the way off the studs without the manifold hitting the strut tower, I couldnt even get my engine into the car with the manifold on.

Changing springs with the head on sounds like a recipe for collets in the sump, especially on the exhaust side, if youre going to that much trouble why not get the guides and seats inspected at the same time.

[walfreyydo]

Thank you so much for the reply and images.<snip>

Alot of those components can only be checked and measured once the head has been removed and disassembled (spring wear, valve stem/guide wear, etc). That said, you can do the measuring yourself if you have the correct measurement equipment but this is often better left to the machine shop who has that equipment. There are wear tolerance specs in the FSM (and the machine shop should be able to confirm). Valve springs are measured in their natural uncompressed state-worn springs wont be as tall as ones within tolerance, so they do need to be removed to be checked.

Valve sealing performance can be checked with a leakdown with the head on, but that will really only tell you how well the valve face is sealing against the seat and if its low, could be due to a number of factors you wont be able to determine until the head is pulled, disassembled and inspected. Its most useful in determining if you have a bent valve from piston/valve contact, but can be used to also look at piston ring health as well (similar to a compression test but gives you more information on where you are losing compression based on where the air is escaping -exhaust valves, intake valves or rings basically).

My S2 head gasket was in pretty rough shape when removed, but still holding a good seal. Hard to see in the photos but a decent amount of gasket disintegration where it covers the cooling jackets and corrosion on the head in those places. Im fairly certain it was the original gasket and had well over 175,000 miles. I was getting compression test numbers in the high 180s to low 190s before removal and well within the 10% variance spec so it seemed to still be performing well. Did not do leak down as I dont have the equipment and already determined that the 968 head was going to be checked, rebuilt and installed in its place.

Lastly I wouldnt assume you need to replace springs guides lifters or valves unless they are checked as bad. These things arent cheap and if still within the tolerance spec, will continue to last, but ultimately thats each persons own choice.

As @Bergerac mentioned, its going to be a challenge to swap out the valve springs with the head on, as youll need a spring compressor in order to remove the keepers and collar (and a magnet to ensure you dont drop the keepers down an oil passage! Ask me how I know) as well as making sure each cylinder is at TDC to keep a valve from dropping into the combustion chamber. The spring compressor I use is a basic C-clamp style and needs to have access to the valve face and goes around the head, but maybe there is a different version that will work without the head being removed. And yes, both intake and exhaust manifolds need to come off.