996.2 3.6 Head Rebuild Recommendations and Estimated Costs

Around 10k miles ago I did a leak-down test and discovered one of my cylinders was down around 18% wet. I had the headers off, and using my borescope I was able to determine it was a leaking exhaust valve. I was thinking it was carbon buildup, and kept driving it to see if it would clear itself up. It didn't, and I believe as a result my idle has gotten worse. I'm thinking it's a bad valve seat, and am planning on pulling the heads off this year to have them refreshed. I know Hoffman will want to replace all of the seats, which is the right thing to do, but I haven't had any success getting a quote from them via their online contact. Has anyone had this work done from them in the past couple years and could give me a ballpark price estimate? I'm also open to recommendations for other shops. Thanks!

Couple years ago forum member Meir had his 3.6 heads done at Hoffman. I saw them when they came back. Thery were done beautifully, some of the best head work I've seen in my half century of doing engines... Hoffman did all valve seats as they tend to be a problem that can cause catastrophic problems on the 996.2 when they drop out. Which seems to happen on a regular basis... He also changed out all the valve guides to a hardened sintered bronze iirr, for a better tight fit as they had loosened up. He also did a stage 3 port job. Looked like he unshrouded the valves nicely. And a sweet multi angle valve job. In my opinion, don't fug around with a leaky cylinder that might be a lose valve seat ready to drop down completely or a valve head break off, you're playing with fire.... He spent $5000 before shipping iirr... Ya, good head work is not cheap and labor is intensive. You will get good head work from Hoffman... A shop that knows/is an expert on the ins and outs of the particular heads they are working on is what makes the difference on engine like the m96. Good tight sealing heads make for a stable smooth idle and let all the max power the lower can make be available. Top notch heads are where the real power is made, in my opinion and experience. Hope this helps.

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Thanks. Yeah the car is off the road for the year until I get that done, replace my throw-out bearing, and put in new injectors.

I jud]srt had a set of 996.2 heads done at Hoffman , full reconditioning with porting. $5000 for all. They are beautiful!

For the sake of conversation, don't flog me to death! I have had many cylinder heads rebuilt. Even on a 356 that I had. But never on a modern P car. With that being said, the process is basically the same across the board. Yes, some specs are very specific but a valve seat is a valve seat. A guide is a guide. Whether you get a 3 angle grind or not is still basic machining. I do not know how much seats/valves/guides are for one of these engines, but $2500/head seems excessive to me. I am thinking 2 hours per cylinder, 12 hours at $100/per hour, parts $250 per cylinder. Just looking to understand the costs. Maybe I need to get my head out of 1998!!!

I too think $5,000 for a valve job is excessive and I would never do that.

I had my heads gone over by Len Hoffman in 2023 when I did a full rebuild to 4.0 due to bore scoring. The cost was a little over $4k. That included pressure testing, ultrasonic cleaning & media blasting, cleaning & grinding the valves on centerless grinder, removing and repairing almost all of the exhaust bolts & threads, new valve seats as these heads have a history of dropping seats, serdi valve , all new guides and seals, new 3.8l valve springs, his "stage 1" porting, diamond milling the decks, re-machining the exhaust flange faces. He even replaces the frost plugs and epoxies them in place. They looked incredible when I got them back from him and he was incredibly generous with his time talking me through the process and make the best decisions. It's just him and another guy Matt that do all the work there. Had the chance to stop in one evening last fall when I took my 4S down to southern Georgia to visit my mom, was super cool to see the shop and they absolutely know what they are doing. Can't recommend them highly enough. The car RIPS now and their headwork absolutely is big part of that equation.

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Thanks! Would you happen to know how much it was without porting? I�m just trying to keep my late-father�s car on the road, not squeeze any extra performance out of it, so if I could save even $1k on the job, while still having it done right, that $1k could towards a lot of other preventative maintenance.

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I know I�m going to be due for a rebuild at some point in the next few years. This was my cylinder 6 when scoping back in 2024, about 10k miles ago (date code is wrong): Planning on DIYing the rebuild so I can reuse anything I�ve recently replaced to keep the costs down, and figure head work would be part of the rebuild anyways. I�m anxious to pull the heads off and check the cylinders directly, and have to admit it keeps me up at night but I have too many car and garage projects before I can get a chance to scope it again.

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Update that labor rate to $200/hr and you'll be closer to 2026 costs. Not all machine shops are good machine shops. Chicago/metro Porsche dealer labor is $319-330/hr, Barnaba Autosport, a top quality independent Porsche shop is at $259/hr I would drive across the country to get competent work done on my Porsche engine for $100/hr

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Absolutely nothing wrong with that (part of the) cylinder wall visible in the picture. Just drive it and maintain it not rebuild it , after you've had the head refurbished.

I had my full engine rebuild done by Slakker racing in Oklahoma. It was a great experience. I�m sure they can do anything you need. Brandon is a great guy. Highly recommend.

I called Len Hoffman a month or so ago when I was troubleshooting a lost of compression issue. I left a message and he called back same day and took plenty of time to talk me through it. He will email you a rate sheet, it's about $1500 for basic refurbishment of both heads. Then he has adders for crack repair, porting and polishing, etc. I don't know if you saw my thread, but the lost of compression on one cylinder on a 99 was due to a valve spring that broken at the first turn. Replaced the valve spring with the head on the engine, put everything back together and it worked perfectly. So what I would recommend is that you drop the engine, pull the cam cover, pull the lifter carrier and inspect that one cylinder valve and lifters. Here is the thread will all the info, most likely will be very helpful to you. If you do the work yourself, it won't be very expensive. For everything I did, the parts were $3,300. I bought 95% from rockauto and FCP euro, it also included the price for the UAOS which was about $750 of that total cost. https://rennlist.com/forums/996-foru...n-buildup.html

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What does the basic reconditioning include?

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Base Service for one pair. Includes: -Teardown, -Ultrasonic clean, -Media blast, -Pressure test, - Clean, inspect & grind valves on centerless grinder .0001�T.I.R. -No valve seat work -Re-machine corroded and/or grooved exhaust flange surfaces These surfaces heat warp and factory steel gaskets etch the aluminum creating potential leak sites. Weather exposure corrodes the surfaces. -Diamond mill decks - Ra< 10 -Ultrasonic & media blast both valve covers, remove old gasket material and epoxy scavenge circuit expansion plugs. -Load test springs -Assemble with stem seals. This service option is applicable if guides and seats are in typically good condition.

Hoffman did mine, but it was much more than just a valve seat. Fantastic work, great communication, fair price.

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Agree on the ~$200/hr. rate. Here in BFE it is ~$200-$240/hr. (NOT Pcar experts....) FWIW: AFAIK Slakker is at $160/hr. Located in Oklahoma City. They do amazing work right In-Shop. YMMV

For the base service, $1500 is fair price.

My full service included replacement of seats and guides Stage II porting and a High rev spring kit

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Agree. This might help some understand the 'why' of total valve seat replacement on m96 engines. As far as i know, this is the deal with m96 valve seats, believe it or not up to the individual.... But keep in mind this comes from a well respected m96 head expert used by some of the biggest m96 builders. Not sure Len will do a basic valve job without seat replacement(?) and warranty it on m96/m97 engines, have to call and ask him, but this is what he has said in the past.... Exact quote copy paste from Len Hoffman Blog "Valve Seat Issues This problem of intake valve seats dropping has struck quite a few owners over the past few years. We first became aware of it with track cars back around 2014. Shortly after, we started seeing seats actually fall out in our ultrasonic parts washer (heated to just 165*) and our casting oven (heated to 210*) during valve guide installs. Lucky for all involved it happened in the shop and not on the road or track. As you can imagine the results can be catastrophic to the engine and the wallet. As a result of these issues, three years ago we began compulsory replacement of all 3.4l 987 (not to be confused with the 996 3.4) and 3.6l 996/997 intake valve seats when we service these heads. In June of 2018 we expanded that to include exhaust seats after seeing several failures. We will not rebuild these heads without total replacement of all valve guides and valve seats. Here are some pics of exhaust seat failures. It�s worth pointing out that the mechanic working on the car made a bad situation worse by pulling a spark plug to diagnose what caused the engine to lock up. The sparkplug was damaged in the failure and when the mechanic pulled it out it mucked up the plug threads. We recommend not pulling the plugs to scope a cylinder on any locked up engine or engine that has clearly suffered a major failure. We can mill out the offending plug in the shop. These heads do not have a lot of meat between the sparkplug and the intake seats for an insert so we always attempt to save the factory threads. We recently had several intake seats drop in the shop on a pair of 3.4 987 heads. We always take measurements when this happens and this time around we decided to snap some pics and share the results. Here�s what we found: Interference fits of a mere .003″. And the thing is, that .003″ was on the tight side of what we usually see. In the past we have measured interference fits as small as .0015″, making those heads ticking time-bombs. We�re pretty sure these heads did not leave the factory with seats this loose. They wouldn�t have made it this long. It�s my opinion that these seats are loosening over time as a result of a perfect storm of valve-train conditions that lead to major valve bounce. These conditions are: worn guides, weak valve springs and aggressive cam profiles. These conditions lead to tremendous shocks to the heated aluminum seat bores, enlarging them over time. Think of the valves as little hammers pounding the valve seats in a wobbling spiral motion. Keep in mind that aluminum softens with heat, making it even more vulnerable to dimensional instability. The intake guides in these heads are very short. Aside from linear valve movement they must also deal with the valve spring wave actions typically present in parallel non-interference dual springs, as the intakes use. These wave actions move up and down the spring and transfer through the retainer into the valve stem leading to lateral and spiraling valve motion during valve events, causing a wallowing of guide material. The resultant hour glass shape of the guide puts the valve out of square with the seat during the valves critical landing point and allows the valve to transfer that wallowing motion into the seat itself. These seats are so hard that they do not wear like typical seats in early aluminum heads. They take the abuse head on and transfer that motion into the aluminum head. Bounce when worn guides are in play will very often loosen valve seats in aluminum heads, especially when performance cams are used. Weak valve springs and worn guides are a potentially lethal combination in a performance engine and can easily lead to catastrophic failure. We machine new seat counterbores for a more shock proof seat with excellent wear qualities. Here�s a pic of a finished counterbore. " Not sure what oem valve seats cost to replace..? $50-100 each..? Len Hoffman replaces factory valve seats with more secure, custom-machined seats to prevent future failures.

Similar to the above, I got detailed explantations from Len throughout my process. The guy is a wealth of knowledge, and his work seems speak for itself. I can't recommend Hoffman Automotive Machine (Hamheads) enough.

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I have used Hoffman. I have a 2000. 996 that had an intermix cylinder number six on the head was cracked. Hoffman redid both heads valve job seats and Springs. He did a great job with a quick turnaround time. Communication was very good. The car is back together and runs perfect. I think he did both heads in a very reasonable price.

My heads got the works from Len Hoffmann during my 4.0 build. Highly recommended!

I got a new borescope and decided to pull the headers off and try and get a closeup video of the leak by airing up the cylinder with some thin oil to watch leak out. I then made an odd discovery: The leak was gone! My current, uneducated theory is as follows: Carbon buildup on the valve prevented it from sealing. Due to Cylinder 1's low compression, the ECU sent more power to that coil/plug, causing the spark plug to wear prematurely. This caused the uneven idle, even though the valve was now sealing properly. Does that sound plausible? Here are some pics of the valves from inside the cylinder, but I'm not sure how much information this provides. I'm still going to do more tests and try to scope all of the valves, but I think I no longer need a head rebuild - which is wonderful, as the car has a few other expensive needs.

Do you have a picture of said spark plug? Ah, I found them in your other post.

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What borescope you're using? It provides very good images.

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Teslong TD300P 5.5mm Two-Way Articulating Borescope. Got it for $106 on Amazon. Smallest head at 5.5mm vs 8-9mm on most of the others.

Your valves look great and isn't the leakdown 10%? If so, just move on and no need to do anything else. Maybe an Italian tune up.