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Major Failure - Valve Seat Ring Broke

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My 03 996 has had a major failure and I thought I'd ask if anyone has seen anything like this happen before. Under very low idle and speed I heard a metallic "clang" noise from the motor and then it died and would not restart. Had it towed to the shop where they had to drop the motor and pull off the 1-3 head to find the problem. One of the valve seat rings on the #3 cylinder popped out and caused damage to the head and top of the piston.

Here you can see the missing valve seat ring and the damage done to the head when it came out. I had him remove the other valve for comparison.


Different angle...


Top View...


Other side of the head. Cylinder 3 is on the right. No issue there.


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First I want to say sorry that you have had this failure. I spend a lot of time on the misc 996 boards and this is the first time I have seen any mention of this failure. I wonder if Jake Raby at Flat 6 has seen this before. How bad was the damage to the piston and were the cylinder walls also damaged? Can the head be replaced or is this going to require a total rebuild with new cylinder sleeves?

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Thanks for the condolences. I'm a new Porsche owner only having owned this car for a little over a year so this is a painful start. I forgot to include the piston picture so here it is. My mechanic, who is very good and reputable, says he can repair the piston and replace the head for a fix. No damage to the cylinder wall. The only risk he says is that if the top piston ring were pinched it would burn oil and smoke. But with the piston in the lowest position where the cylinder is tapered out he was able to move the piston side-to-side and see the ring and it appears to me moving freely. He's going to do a "leak down" test once the new head is installed to check it. Fingers crossed. My mechanic has also never seen this before in many years of working on Porsches and building/re-building racing engines. The only reason he can come up with is a faulty head from manufacturing. Somehow the seat ring didn't get the proper seal when installed into the head.

View of damaged piston..


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  • Moderators

Such fractures occur in all brands of engines, they are not Porsche specific, fortunately not much. I have have seen this on the air coolers also during the years. Unfortunately it occurred to you.

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  • 8 years later...
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11 minutes ago, tony z said:

I see that some say that all valve seats should be replaced during a rebuild. Problem is it seems that Porsche doesnt list them on their parts list. 


Anyone got any idea how to proceed ?




Replacing the valve seats is not a DIY type job, and should only be handled by a machine shop set up to do this type of work.  The seats are an interference fit and will need to be machined to spec after being properly installed into the cylinder heads, so the insert is not specific to Porsche.  I would have the heads checked by a reputable shop and let them determine if any seats need to be replaced.  Normally, they are just machined in place unless more work is required.

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1 hour ago, tony z said:

Thanks much appreciated.


So if porsche dont sell  valve seats I presume the machine shop can fabricate new seats ?







Aluminum cylinder head material is not strong enough to simply cut a valve seat, so a much stronger material insert in pressed into the head to do the job.  This is common on all aluminum cylinder heads, regardless of brand.


The way it works is the inserts come in a variety of sizes, the machine shop can chose the closest match and then cut them to size and install them (an entirely different procedure involving heating the head casting while chilling the insert), and after the head stabilized to room temp, the shop can machine the valve seat to match the actual valve itself. 

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