Doug Donsbach

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?

Dharn55

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.

Doug Donsbach

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.

Jake Raby

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.

Doug Donsbach

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

Carrera Mike

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

flpaindoc

subscribing...

sehorntx

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!

Meister Fahrer

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!

Doug Donsbach

Good luck!

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

Dharn55

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.

redridge

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

Blackness

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.

nycebo

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

htny

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.