1991 C4: 3.6 out for headstuds and more
 

Hello all

This is Rus from CT. I used to own a Carrera, whose top end I did with a massive amount of help from this forum. I sold that car to a great guy I met on Pelican and have driven an E30 since. I just sold the beemer as I got a deal I couldn't refuse on a 964. I found a broken headstud (#1, top) and so pulled the motor.

The plan is to replace all of them with Supertec units, which I have in hand from our host. I have budgeted to have the heads looked at at at minimum clean/surface, but obviously address anything else that's needed. I'm sure they'll end up with new guides but will rely on my machine shop who does many heads per week for guidance.

I'm not necessarily looking for performance or big upgrades just to get the car back on the road, the right way.

I'm posting a thread now as I get to the "real" part of the project. I am shopping for the all important gaskets and chemicals and came here to get the latest and greatest recommendations.

When I did the 3.2 there was an all inclusive gasket set from Wrightwood which 'curated' the best of each selection. At least that was my memory - I'm sure I shopped around for other parts.

For the 964, Wrightwood makes a chain housing kit that I was planning on using. I would love to hear recommendations from others who have done this work on all the sealants, gaskets etc they used. My base presumption is to use what worked on the 3.2, when applicable.

The motor is up on a stand and I'd hoped to have the heads off this weekend but can't get to the last three heat x hex nuts and have some offset wrenches and swivels on their way to me next week.

One observation I have to share - since I was waiting for a loaner P201 tool (thanks John J!) I decided to strip the motor before dropping it. I was very happy with this approach as it gives much greater visibility to whats going on during the drop and greatly lowers the total height the car needs to be in the air.


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993 Twin Turbo head studs are the best.....

The 964 cylinders seal to the crankcase with orings rather than with copper washers as on earlier engines. My 964 leaked copiously at this spot, and when I pulled it apart I found that the orings (which have a very small cross section) were all hard as rocks! So, I would definitely recommend pulling the cylinders and replacing the orings at the bottom, even if you aren't planning on replacing the piston rings. Also, be aware that the 964 cylinders are tapered to reduce piston slap if you or your machinist measure them with a bore gauge. As I'm sure you know, heat is the key to easy removal of the head studs.

winders - I should have clarified that I already have the Supertec headstuds/nuts

RedCoupe - mine is leaking a little at the base of the cylinders also. I will be removing the cylinders for the reason you mention - to get heat directly on the headstuds for a nice clean pull and so I can clean the threads before installing the new ones. The base gaskets are on my shopping list. Haven't decided on rings yet. My shop has a hone setup for Nikasil jugs and so it is tempting to go ahead and re-ring.

I disassembled the chain housings today and found a good deal of white sealant, believe RTV for the way it comes off in strings. It looks like someone has been here before. I also found 993 chain housing to block gaskets - are these considered an upgrade from the 964 paper ones? They certainly seem more substantial. Part 99310519300


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R-mm, I would be careful about honing the cylinders for re-ringing. There is previous discussion on this forum about this, but the issue is that Nikasil is so hard that once it is roughened, it will just wear the new rings out rather than smooth out like cast iron. So, you need to start with a much, much smoother surface than is typically done with cast iron. I would want a shop that hones my cylinders to have a profile meter to measure the surface to make sure it's within parameters for Nikasil. On my 964, I'm using the scotch-Brite method.

My shop, who does work for most of the local Porsche shops (and some extremely hi end stuff all the way to four cam) specifically volunteered that they have nik and alusil appropriate hone setups and have succeeded in re ringing both. That said the motor has 60k miles and if things look as good as my 120k mile 3.2 did I may very well leave the rings in place.

Last night I removed the rockers, cam and cam towers, which promptly went into the ultrasonic for a nice bath. I then removed the heads but stopped at the jugs. I can't recall if there is a technique to removing them in a way that is safe for the rings - I will do some research or does anyone have a description to offer?http://forums.pelicanparts.com/uploa...1580948194.jpg
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Parts are with my machine shop who recommended honing the nikasil cylinders - he has a setup dedicated to these types of cylinders and was conversant in the challenges of working with the material. I will then re-ring using stock type rings. PP sells both Mahle and Goetze, I have used many products from both companies on many German cars - does anyone have experience with their rings, specifically for 100mm bore cars?http://forums.pelicanparts.com/uploa...1581004543.jpg

Not splitting the case? I would.. and did.
If you insist on not splitting the case, you might still want to change the o rings on the through bolts.. they can sometimes leak. You can remove 1 bolt at a time, and change both the o rings..

I always try to balance leaving well enough alone and doing the right things while I have access. Splitting the case definitely was not on the agenda as this is a 60,000 mile motor that so far has looked perfect with the exception of the one head stud That sent me down this lath. Your idea about replacing one O-ring at a time has been mentioned to me elsewhere I could use the groups guidance on this. I know there is the possibility of tearing the rings as they go in and creating leaks as opposed to solving them.

On the under other hand I have been thinking that when I heated up the base of the head studs to loosen the old Loctite the heat was adjacent to those through bolts

I don't think the heating of the case to loosen the head studs, would affect the o-rings.
When pulled my 60k 964 motor, I found that the o rings were half torn from initial install.. (or maybe I did it when removing them?) I elected to do the bottom end purely since I had come all this way. As it turned out, all my bearings, mains and rod, were in excellent condition. Only the IMS bearings were down to the copper in some spots.

If you do change the o rings, just make sure to not allow the bolt to turn as you tighten down the nut. You'll be fine.

I can not find a piston ring gap or ring to land spec in the Porsche factory service literature. Can anyone point me to this?

The ring gap and service limit on the ring grooves should be in the 964 Technical specifications book (at least I think that is what it is called). I'll pick mine up when I'm over at my shop tomorrow, but if that small binder is still available it's well worthwhile to buy a copy. As far as splitting the case, your engine is low mileage, but do you know how it was driven/maintained during those miles? My engine at 150k still had excellent looking main and rod bearings but significant wear on the intermediate shaft bearings. And, with splitting the case, you get to completely clean it including pulling the plugs on the crank and flushing out the oil passages.

Thanks a friend sent me this from that Bentley tech specs book which I ordered a copy of yesterday.

Attachment 10541

I received some parts from Delaware Porsche (NB: I have spent four figure sums with our host for this project also. sometimes stuff isn't in stock) including cylinder base to block o-rings and was expecting green (viton) which I believe is what I removed from the car. I received black as attached. Genuine Porsche. Do these represent the latest and greatest or should I be looking for another o-ring?

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I've now got the cylinders installed to the case and heads installed finger tight.

When I assembled the 3.2 I put the heads on the cylinders finger tight, torqued the cam carrier to the heads then torqued that assembly to the case. I did this at the recommendation of this forum and wayne's book. It worked out leak-free.

The 964 factory manual is is not really 'sequential' per se and I have trouble figuring out if this is the recommended assembly sequence. How did you all approach this?

Also wondering if anyone here has rebuilt an early 3.6 link mine without head gaskets and whether they assembled bone dry or with any type of sealant on that mating surface?

My early 964 is going back together with a set of later model cylinders and Pistons, so I can't advise on what I would do for reassembly. However, there was no sign of any sealant when I pulled the cylinders and heads apart. I believe, just like the 3.2, that the seal is from a finely machined surface that is cut at a slight angle, not from a sealant.

I bet that white goop you found is Dow 730. Bruce Anderson had mentioned that as a viable sealant alternative and it wouldn't surprise me if someone chose it because of Bruce's mention years ago. That said, the way it was applied to the cam box thrust plate and the intermediate shaft cover is criminal. If the o-ring seal was properly replaced, no need to use that annoying goop there. Belt and suspenders approach isn't necessary! Instead, use some Dow 111 or 112 o-ring paste to coat the o-ring and preserve it from future oil contamination/hardening.

By the way Viton rubber is not only green. It comes in black too.

I agree with mikedsilva that replacing the through-bolt o-rings is a wise thing to do. Last thing you want is a leak happening shortly after you've done a thorough top end job. You could remove your cam housings and heads as a bolted assembly and easily address the through bolt o-rings. Here's the recommended procedure, starting on page 86

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