Carrera head studs
 

Yesterday i was doing a valve adjustment job and upon removing the bottom left cover the heads of 2 head studs fell out. Both were on the catalytic converter side so it did make some sense. There was never any symptom of this anywhere, no funny sounds, etc, so from what I can deduce I caught this early enough to safely assume there isn't any internal damaged to the head or block.

After a bit of swearing I still need to fix the car. I simply can't do this job by myself in my garage for various reasons so I did some reading here and started calling local shops. Car is a very early 3.2 Carrera Targa (built 8/83) with about 149K miles on it.

From what I gather people are recommending a valve guide job along with head studs. A couple of shops I called also recommended an complete valve job along with a ring job at this mileage. Should I go for it?http://forums.pelicanparts.com/uploa...1524249061.JPG

I think you need some data to help you make your choices. First, do a leak down test and see how the cylinders with intact head studs are doing. If they are OK, I would leave the rings alone.

I think valve guides are a given, so a valve job is in order. While the heads are off, check the cylinder walls for being scratched, and measure the bores. Scratches and/or out of spec diameter warrant replacing the cylinders, but I bet they will be OK. The lower studs should all be replaced.

At least they broke off near the top. This leaves a lot of stud sticking out of the case so they should come out with heat and a pipe wrench.

How did the car run before? blow smoke or use oil?

Compression and leak down are a good idea now.
Rings are relatively cheap so might be worth replacing. I would.

The lower studs break due to corrosion more than intense heat. I have an '86 3.2L apart that had a broken lower stud on the other side of the engine (forward-most stud, which is cylinder #6) and it has only 78K miles.

It's hard to tell a shop how to do their job but this could be done rather inexpensively if the valve guides are still OK (it's reasonably possible the guides have been previously replaced) and the pistons are left in the cylinders. Then you don't need to do anything to the heads other than cleaning off the old sealant. Regarding the rings, you slide the cylinders off just enough to expose the wrist pins, remove the circlip and knock out the pin. Then your rings remain basically undisturbed. Take off all the cylinders like this and you have access to replace only the problematic lower dilavar studs.

The downside to just leaving the pistons and cylinders as-is, is that you are ignoring any ring, piston (typically the top ring groove in the piston is the potential culprit) and cylinder wear. Plus the cylinders often have some fretting on their head sealing surface that should be touched up with some very light machining. That means it's also a good idea to oh so lightly machine the head surfaces as well to remove the surface defects.

The car ran just fine before this. Which is why were both in shock when those heads fell out as absolutely nothing indicated their breakage. It may have used a little oil but if it did, wasn't much.

I'll see if I can get those tests done. May have the shop working on the car do it although their incentive would be to pronounce everything bad to make more money. :)

One shop actually recommended putting everything back together and driving as is. I've seen that advice before too as from what I gather there are several other pieces that hold the head to the block, not just the studs. Do you guys think that was back advice? I don't want to wreck the engine or the head, they're precious to me. :D

I would definitely not go with the "drive it as is" suggestion. There are four studs holding each of 6 heads to their respective cylinders and by extension, the crankcase, nothing more. Sooner (probably) or later (maybe), the sealing surfaces of the head and cylinder will be damaged from combustion gases leaking past them.

You are in a tough situation. Some shops will suggest more work than what is absolutely necessary after your motor is on the bench. Maybe they are just being overly cautious or perhaps they are taking advantage of the situation and you.

Talk to different shops and ask if they are OK only doing what really needs to be done.

If you have some history on the motor it could help. Has the motor ever had any work done?

IMO, I can't imagine, although it's possible, that the valve guides are still in spec. I would at least plan on a valve job. Also, as mentioned, have a good look at the cylinders. It is entirely possible that they are still good. But they should be measured. If they are still good and the pistons have not been removed, you are good to go. Worse case scenario is you will need new or rebuilt cylinders, so be prepared for that possibility.

You might want to buy Wayne's How to Rebuild 911 Motors. It will give you plenty of background so you can have an informed discussion with your mechanic.
https://www.pelicanparts.com/catalog/accessories/rebuilding-porsche-911-engines.htm

I have records going back about 10 years, that's all. There is no mention of any motor work aside from the usual oil/filters/valve maintenance. According to my friend/mechanic it has not been apart. I did have a motor issue with engine seizing at specific times but after a lot of screwing and guessing it ended up to be what I should've replaced in the first place - the DME unit. On the bright side while chasing this glitch I replaced starter, all 3 left-side sensors, maf sensor, DME relay and a couple of other things besides the computer itself. Finally got it running like a top all the way until yesterday when the stud heads fell out. The actual engine case didn't even leak any oil shockingly. Just sweated a little around the seam but didn't actually leak!

Looks like I'll have to go through a bunch of shops. I'm fine with doing a valve job, I'm willing to invest money into the car to make it as solid as possible. I already spent a ton of time and money on it so I may as well. But at the same time I'd rather not spend money on stuff that is not necessary obviously.

At a 149k miles, I’d go ahead and replace rings. Nikasil lasts forever and you’d have nothing to worry about for many years to come.

You can totally leave the bottom end alone and these things last virtually forever having 8 main bearings. As long as it never suffered detonation and the oil changed frequently, the low end should be fine for a long time.

Don't some of the Carreras have alusils?

I will do the valve job as a matter of course at 150K unless they have been done before.

Leakdown test will tell you if your rings are bad.

My 2c.
Good luck !

Think so, but not sure

Let me start off by saying, I do this for a living, so this is based on how we would advise and go about this. As a business, we must have your best interests in mind and eliminate any chance of continued failures. To do this, we must look at everything and leave nothing to chance. Its that old story, you do it and it fails, and everyone has sympathy for you. A business takes the same approach and they are the devil.

At this stage, you cannot leave anything to speculation as it can include huge amounts of erroneous results.

Look at what you have. You have a 149K mileage engine. That’s high mileage and some wear has taken place. How was it driven is very important as is the regular service intervals where clean oil and dirty oil filters were added and removed. You have two broken head studs and possibly more about to fail.

Forget about having the leak down or compression checks done at this time. The results can be deceiving with broken head studs. Some of the other studs probably have lost a lot of their tension and not holding the heads down tight. The Cylinder heads must come off to replace the studs and the valves can be vacuum tested, then. The Valve guides need to be checked and to do this the valves need to be removed from the heads. While the valves are out of the heads, the stems and guides will be measured for sizes and the seat and valve margins can be inspected. If the guides are replaced the seat must be recut.

To replace the head studs, the cylinders will be removed. At this time the cylinder bores can be inspected, and the sizes checked. The pistons can be inspected, skirts measured, the ring faces checked for wear. Before the cylinders are removed, the ring sealing can be checked, by the same way the leak down test is performed. Same tool, and a simple plate bolted to the cylinder. Although this will be impossible on the cylinders with broken studs.

If this was my car, I can use some risk management here. This is easy for me, as my company would do all the machine work and the assembly labor. I buy the repair parts at wholesale, so I can make some decisions at a slightly lower risk than the average owner can.

Once I had the cylinders off and the pistons, rings measured and inspected, I would remove either or both the #2 and #5 connecting rod. Inspecting the rod bearings on these two rods, (they are last ones to get oil) I can assume that the main bearings are good, and their clearances are within spec. I cannot tell if the oil pump is good or the timing chains have not stretched, only your records and some hope can give these assurances.

As a business we want to check everything. We must be sure you are getting a perfect engine. We cannot leave anything to chance. It’s not about money and the cost, it’s about giving the best service, and caring about what you do. This is the difference between those that charge a lot and fail to perform what is required, who take short cuts either by not knowing or understanding what needs to be done; to those that do it with complete attention to detail.

Make your choice.

Well said Neil !
Mike Bruns

Thanks for chiming in Neal. Sounds like you have all the bases covered.

Awesome stuff, Neil Harvey. Always good to hear from the pros.

Sounds like a handy tool to have.

Yes there are Alusil cylinders installed in some Carrera engines and it's a very good point to bring up in terms of re-ringing those cylinders. I would have the Alusil cylinders plated with Nikasil.

I remember Sir Steve Weiner state he has never seen Nikasils worn out. Cylinders ovaled, yes, but not worn out if Nikasil plated.

Hope I quoted him properly....

Thanks guys. Special thanks to Neil for all the info. Very useful stuff and something to ponder on.

Talked to a couple of shops. One quoted me $20K, the other $10-15K. Of course those are worst case scenarios where you replace everything but Jeezus! If a rebuild costs $20K do I junk the car now? :(

Lots of cars used to be parted out. Now with the current value of these cars you won't see that much anymore.

The two big expenses are replacing or re-plating the cylinders and the labor if everything needs to be done. Then the little stuff can add up while you are in there.

Sounds like Neal has the correct approach how far is he from you?

A lot of us do our own work, it just takes time, money and experience.

Good luck.