PC-85-928S

i snapped the lower cam cover shoulder bolt.
I started drilling it out in the center, increasing the drill bit size.
Should I keep going?
With this prevent me from putting in a new bolt if I go to far?

Landseer

My experience is that yes, you can rethread with same size.
Like Dangler says, prevent overdrilling from a width perspective.

If you can switch to a left handed drill bit it might wind out.
Don't use an easyout though, too risky!

H2

And be sure to use the proper size torque wrench on the next one you install. These large head, small bolts snap off really easy. Also, you don't want to partially separate or weaken the new bolt when you screwing it in and have it break off while you're at speed on some lonely road. The large, heavy duty torque wrenches might not be accurate enough.

blown 87

Most torque wrenches are only accurate with in the top 80% of the range.
I try to select one that is around the top 25% of the range unless it is a digital one, then it is not as important.

GregBBRD

You have found the weakness of the early '85/'86 cam cover hardware. Those shoulder bolts break off with alarming frequency. Porsche superceeded the cam cover hardware, late in 1986....but that hardware is NLA and finding used, updated hardware is pretty hard. 928 International always has it, but they have a really tough time picking it out from the later valve cover hardware. I always need to drive over there and sort through that hardware, whenever I need the updated hardware. Plus that, getting all of the shoulder bolts out of an installed head is very difficult. I usually just install another shoulder bolt...which are also NLA.

You are never going to get that piece of spacer out of the head and be able to rethread that hole, without some serious help. First of all, those shoulder bolts are put into the heads with the best Loctite I've even seen....Porsche didn't ever want those things to unscrew with the upper bolt.

Drill yourself the most perfect hole you can, keeping the drill perfectly centered. Then heat the hell out of the area surrounding the broken piece....heat until you can see the Loctite bubble around the threads and smoke. Remove the heat source, and immediately install a high quality extractor. The broken piece will easily come out. If not....you didn't get it hot enough. There will be no damage to the threads, if you do this correctly. The problem is only the Loctite, not the threads.

blown 87

I can not speak for you, but I would much rather tackle a job like that before the owner makes it almost take heroics to repair the bolt hole. (drilling off center, on a angle, broken bits, extractors, etc) cause that kind of stuff really makes a bill go up.

GregBBRD

You speak the truth....and I'd be glad to let you speak for me....which is why I tried to tell this poster how to fix this, the best way.

I've seen dozens of these heads with the broken piece still there and a big chunk missing out of the aluminum head. The head is very thin, in these areas and any "ham fisted force" ends up breaking a chunk out of the head.

Here's the long version of the required repair:

Perfectly centered drilling. If you can't drill the hole perfectly straight, in the center of the broken steel part, quit now.

Only drill as big as necessary to get the best extractor in the hole you can find.

Understand that most all extractors are junk. Buy good ones. Snap-off only offers one kind that works. They are short with a hex head. Come in a set with a bunch of size steps. Use the exact proper drill. Their left hand drill/extractor set is only good for removing broken off plastic plugs in radiators and removing things that you could have gotten out with a sharp pick turning the broken piece backwards.

Heat the hell out of the area...hot. "Map" gas might work...but you will need to be patient. Propane alone will not do it. I've never had "map" gas....I use Oxygen/Acetylene to heat this area.

Heat enough for smoke to pour out of the hole. Look for the Loctite to bubble between the broken insert and the head.

Allow this to only cool as long as it takes for you to "tap" the extractor into the hole.

Remove the broken piece. If done correctly, you probably won't need to chase the threads.

Loctite new shoulder bolt into place. Do not overtighten the hardware! This is why the shoulder bolt broke, in the first place. The sequence of events is like this: Valve covers leak. Owner/shop tightens the crap out of the hardware, which bottoms out the bolts into the shoulder bolt, which "twists" the shoulder bolt at the base of the threads. Shoulder bolts break when someone attempts to remove the bottomed out bolts out of the valve cover.

I sell a proper rubber coated washer to seal the valve covers, which are NLA, from Porsche. I literally hand make them. Use the stock "0-rings" additionally.

Dictys

If only I had read the above first would have made my life easier.

I have just removed a broken cam bolt on my S4, the problem as it was a lower cam bolt was access.

Once I had removed nearly everthing from the surrounding area I used a right angle drill to drill a small hole in the center of broken bolt, then used a micro bolt extractor on a reverse thread and it came right out.

The set of extractors I have a left hand cutting edge on one end and a left hand thread on the other, you use the cutter first then flip the tool over and use the thread in the hole aready cut.

blown 87

We both had removed literally thousands of broken bolts, some in areas that are not critical and others places that would make Smokey apprehensive.

And it never fails to amaze me that some folks are willing to try to remove very critical bolts, in places that failure to do it perfectly, will end up costing thousands of dollars.

And that some times it is the very first broken bolt they have EVER tried to remove.

Ignorance is bliss I guess, until the bill comes due.



I had one today, I made two cars pass a ODB11 test pass the emissions test, and he wanted to know how come the labor was so much, I charged him three hours and took both cars to get inspected.

His total bill was less than 750 bucks.

Ya just got to shake your head at times.

This is not directed at the OP, he may have done this many times, I do not know.

Landseer

There are some 928 cars here on RL that are so valuable I wouldn't drive them, let alone try to drill out a bolt.

Lizard928

Step 1 remove head
Step 2 take head to machine shop
Step 3 pick up head!

blown 87

That is always the safest way for a mechanic from a $$ point of view, on the hope that the machine shop guy is better than you are at removing broken bolts.

Not my first choice.

blown 87

Closet waxer you are.

Lizard928

If I had a milling machine I would do it myself Greg.

But if I didnt there are somethings that I simply will not touch. If I had one of those bolts break, depending on where it was I would be telling the owner that the engine would be coming out to complete the repair.

I would then also be looking for ways to ensure that the drill bit was perfectly centered. Although, if I get an early car with this style, I for worn my customer about this possibility prior to the work commencing, and I then update them to the new ones. When the old ones are being removed I use an ample amount of heat as if you dont use heat, they WILL break.

Landseer

Yup, not a hair. Some of this stuff is worth more than our house.


Wish I'd had that expert advice GregB gave.
Mine was a perfectly centered hole, followed by a broken easyout.
(didn't think about loctite)
Then diamond bit ginding, overdrill and helicoil.
Then refit the shoulder piece with a new bolt end.
Took something like 16 hours.
Had packed the head with wax paper, then clean rags, and ran constant vac to remove grit.