Intermix problem, Found the crack.

Some of you may have been following the problem with my car a 2000 C4 Cab that had an intermix problem last September. I am one of many that have posted here with the issue. Well today I found the source of the problem and here it is At cylinder #1, by the inner exhaust valve, right where Jake Raby told me to look, and right where Doug Donsbach had his. So I am a cylinder head away from being back on the road. While some say you need to totally rebuild the engine due to the chance of bearing wear after the engine has run with coolant in the oil, I am going to chance it. I know 928 owners that have over heated an engine and froze it up, let it cool, changed to oil and driven for another 50K. And at ths time I don't want the expense and challenge of a total rebuild, too many specials tools and the installation of pistons 4-6 is a tremendous challenge. In any case, with the exception of a bad oil cooler, which is seldom the source of an intemix problem, a cracked head may be the best case. Head are readily available, and not that hard to change out. Getting all the crap out of the cooling system is probably more of a challenge than changing out the cylinder head. So I am about a s happy as I can be given that I had the intermix to begin with.

That's so close in location to the crack I found in mine it's spooky! Sorry it wasn't the cooler, but at least now you know what you're looking at. Wanna try to get a group buy on rebuild parts?

Might work. I looked in my PET and it shows three numbers for what appears to be a cylinder head assembly (valves but not the cams, folloer etc. 996.104.003.02, 996.104.003.03 and 996.104.003.05. Doens not really differetiate what each is. When I looked at the pricing on Renntech.org, if you input 996.104.003.02 it shows superceded by 996.104.003.05 at a price of $1,998.78. If you input 996.104.003.03 it shows superceded by 996.104.003.05 at a price of $2,036.77. and if you input 996.104.03.05 it show a price of $2,695.92. Not sure what to think. I am going to call Sunset and Suncoast tomorrow and see what the real story is. If you can get an assembly for $1,998.78 list, then the Sunset/Suncoast price might be alot less, cloise to what some wreckers seem to be asking for a used head. Also, a group by on the special tools, or just sharing the cost and passin gthem around might be worth while. It really is spooky how close it is to your crack. But I bet Porsche would say it is just a coincidence, that has probably happened hundreds if not thousands of times.

great find! thx for posting... good luck with it...

Thanks for posting. I hope it all works out. Makes sense what you are suggesting.

Wow, those look like identical cracks. It would be hard to believe that it's not a manufacturing fault. Good Luck on the fix.

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Engineering is where I'd place the blame.

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In my mind as a layman, I'm thinking something, directly or indirectly, happened in those exact spots during casting, to affect the integrity of that particular area. Most likely it was just one or a few batches of production.

Glad to see I was able to help.. Give me a call tomorrow and let me get you some prices as I have some lines on these parts that others do not and I may even have a good used head.. I'd just need yours to measure the chamber volume from to ensure a match.. Congrats on the fnd!! BTW- manufacturing isn't what creates this crack, it's thermal shock loads that find the weak link.. This crack only occurs in the engines installed into 996s from what I have seen thus far having diagnosed dozens of them.

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No, manufacturing didn't create the crack, of course not. But manufacturing faults created the weak link for the crack to be possible. If there's more than a few similar incidents, then Porshe is to blame.

Trust me, I agree with you 100%... I have seen fiorst hand more instances of this than probably anyone outside the Porsche reman factory.. This is one of the 17 MOFs (modes of failure) we have documented from the M96 platform.

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Well, Dharn's is a 2000 and mine is a 1999. Potentially, that represents a lot of space between batches.

My 2000 was manufactured in late 1999, so there may not be that much time between them.

How do you know the manufacture date? Mine says 2/98 on the door tag but the VIN decoder at Renntech.org says it was built in 1999 and has chassis serial number 0368. Where is the engine serial number located? As an aside, I just had a good laugh by reading the top of page 184 in Streather's book regarding the causes of cylinder head cracks: it all boils down to owner abuse!

I found some tags on the body that show 10/99. Also the car was delivered to the original owner (I bought it in 8/00 with 4,000 miles) 2/23/2000 so it had to be made in late 99.

Just looked at the P.O.'s paperwork and see that mine was purchased new on 4/28/98. So, I believe the 2/98 production date is correct. I wonder how many 3.4 heads they built to span 20 months worth of 996 production?

If you talk to the wreckers and shops there are alot of cracked cylinder heads, usually #1 at the inner exhaust valve spring seat, or the #6 in the same spot. I wonder how all of us owners are abusing that particular area fo the head. Maybe it is a conspiracy by us owners. So the cost of a new head is $2,695 list, $2,294 at Sunset, in Germany so one month out, or a premium of 20% for a quick ship. That is a full head, except cams. gears, etc., but all valves, springs, can cover. etc.

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That sort of makes sense, as the 1-3 bank heads and 4-6 bank heads begin life as the same casting and are differentiated by some relatively minor machining steps later in the production process. So the #1 and #6 combustion chambers are really in the same place on the pre-machined head.

Correct. This is the thinnest portion of the casting and doesn't have sufficient cooling characteristics either.. I have been making some precautionary measures when we reassemble engines with these heads, it would suck to lose one of opur engines because of this inherent issue that we can't overcome without a new casting.

Maybe they should have air cooled it. Oh hey, wait, that's an old idea, isn't it?

Dharn, Good job and effort finding cause. Hope you get it fixed and be back on the road soon.

subscribing...

Have same intermix problem in my 99 C2 996. Had oil cooler replaced as well without resolution. Bought a disassembled engine from guy in Miami 996. Have all engine components. About to start dropping my engine and looking for my cracked head in the same place as yours!

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Crikey, not cheap for a cylinder head, but I'm thinking aircooled VW prices, ha. So not bad in the scheme of things. Thanks for the post, and interested to hear your progress and experience. Good luck!

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Good luck! Be sure to start with the 1-3 bank, as that's where you'll likely find the crack.

I remember seeing that engine on Ebay. Thought about making a bid. The price was really good for a complete (but disassembled) engine. Less than some are asking for just a head. As I remember it had a spun bearing. You might want to check the 1-3 head you bought to look for cracks. They say you can remove a head without dropping the engine. But I think the extra time and aggrevation is not worth it. Now that I know where the crack in my head is you actually could see it by just removing the coil pack, and plastic tube on cylinder #1. But I did not see it until I had the cams out and removed the cam follower tray. If you get some penetrating dye (Magnaflux make one) and just use a small paint brush you culd see it better without taking the head apart. that way you might know where the problem is before you do too much disassembly. I could not find the dye locally, so I started disaaembly with the 4-6 side, only removing the cam cover, then by chance went to the 1-3 side because I could not find the threaded rod to compress the cam advance tensioner. Thankfully I went ahead with the cam removal on the 1-3 side first and found the problem before tearing apart 4-6 any further. By the way, if you need a threaded rod for compression the cam tensioner let me know. there is a small quirk on these. With Doug Donsbach's car, an early 99, he was able to use a standard (right hand) threaded rod, but on mine, a 2000, the threads in the tensioner are left handed. As I could not find 5mm .8 threaded rod I bought a die that size and made it out of brass rod, then found out about the reverse thread. Yesterday I ordered a 5mm .8 die with reverse thread and will thrad one end of a rod with the left had threads and the other with standard threads to make the tools. I can always make up another now that I have the die. But if your is a 99 you may have the standard thread. PET shows one tensioner -98 and a different one for 99+. I think Porsche did the reverse threads just to make it hard to service without the special tool. the really is no possible explanation for the reverse threads.

Thanks for all this info guys... Dharn55 best of luck with your rebuild!

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Jake, can you explain "thermal shock loads"? Is it a common scenario, (cold start, warm-up, cool down)? Some abuse like hard revs and high loads on an engine that's not up to temp? Or just inadequate cooling? Etc., etc? Particularly as it pertains to the M96 engine.

this is a phenomenal and very informative thread. It's shocking what some of you guys know!

So it's "ask a stupid question" time: JB Weld or equivalent into the crack before you go as far as replacing or is here just no shot of it curing hard enough? Since it's all the way up there in the head, I don't think you need to worry about any exotic materials, should be straight aluminum (which is hard to weld with heat but maybe there's a filler, all I'm suggesting). Also another stuuupid question since I'm on a roll: When you buy that part for 1995.00 ish, is that a) one head, b) a set for the whole bank of 3 or c) a set of heads for both sides? Are you concerned at all with matching the volume/flow etc? Would having one brand spanking new head or even one bank throw you far enough out of harmonic balance to cause a lot of problems elsewhere? Its a ten year old motor and will not have blueprinted dimensions or flow characteristics, that's all I'm saying. Anyway, best of luck, I think between Jake's experience and your willingness to give this a shot, we will have valuable new information on inexpensively solving a nagging issue for everyone.

I am not familiar with JB Weld. I have talked to a machine shop in Costa Mesa that is quite familiar with these craqcks and says they can repair them. They take out the valve guide and seld the carck, machine the area and then put in a new valve guide. Will also do a complete valve job (not new valve but grinding, etc.) as part of the process. They say then have done many of these. I know I did not even have to describe the crack to them, as soon as I told him I had a cracked head on a 3.4 996 he staid "#1 cylinder, inner exhaust valve seat, runs to the spark plug chase, see them all the time, fixed many of them." As to the new head, the list price is $2,695, so you can get it for about $2,300. It is the head with all valves, springs, etc., the cam follower with tappet covers, and the Cam cover, but does not include the cams and gears, etc. The set has to include the cam cover as the cover serves as the top race/cap for the cam bearings and is lined bored with the head casting, so they are a matched set. Jake Raby did say that he would measure the volume of the head being replaced against whatever head (new or used) that is replacing it as there may be variance that could cause a difference in compression and through CEL's. However, just worn valve, rings etc. can cause a variance in compression. Jake is great, and incredibly knowledgable, but is a perfectionist. As he states, he is unwilling to put anything out of his shop that could lead to bad results, warranty claims etc. He does premium work.

Yeah jb weld I wouldn't trust anyway, just threw it out there as an example because it's the most commonly known "cold weld" filler to most folks. I just figured there was some sort of suitable cold weld / filler/ sealer for aluminium that you might have uncovered in your research. Not a real fix if you can properly weld in there, which it seems from your shop's experience you can. I'm glad you already asked yourself the compression questions. Looks like you've already really thought this through, found some smart guys with experience, and let's pray for a perfect fix. One word of caution, if it's Motormeister (IIRC they are in downey and not costa mesa, but I can't remember for the life of me) run from them, they have so many bad stories out there. If it's Euro Collectibles, Honest Engine, or Performance Developments I haven't heard anything bad, and you know the only people who speak publicly about work are those with complaints so that's a good sign. Still make sure you check everyone out seven ways to sunday. Are you sending out the whole motor? I would if I were you assuming it wasn't too cost prohibitive, would want to bench test compression a bunch on the existing block. 2300 bucks for one head (fully dressed or not) is a big number, but not new engine big! Thanks for clarifying

This is the shop that does the repair. No connection to Motormeister that I know of. http://www.engine-machining.com/ John Edwards seemed like a pretty straight shooter when I spoke to him.

I don't know him, but I did google and see a video of a cracked and weeping boxster motor posted by him on youtube. Out of prudence, I would search here, pelican, renntech, 6speed, flat6 and see if anyone's used his shop. Good luck and keep us posted!

Dharn, Sorry I have not gotten back with you.. My source did not have a new head for that cylinder bank, but had plenty of the other side... They are still looking for one, though.. The used head that I have was also cracked upon closer inspection, but I may have a line on another one. Some cracks in heads can be repaired. My cylinder head tech is the most excellent I have ever seen with welding aluminum and repairing/ straightening heads. The issue with this crack is where it is located and how difficult the area can be to weld, its risky to say the least. I do not associate myself with any risky repairs/ fixes... Thats because if something we worked with does break it compromises the entire engine program.. I'll continue to search for a head for you, call me if you find something before I do.. (I am slammed so you'll have to leave me a voicemail)