earossi

I am in the process of doing a cam service on my 93 968 to change out the cam chain and the wear pads for the chain. There have been a few well written articles on this site describing how to go about the work, and all have mentioned problems breaking loose the cheesehead bolts that hold down the camshaft bearing caps. The cheesehead bolts are just too shallow to hold the cheesehead socket without stripping when a large amount of torque is applied.

In the past, while working on socket head cap screws on motor cycles, I had come across a hand held impact tool that has always worked on bikes. You simply put on the appropriate socket and then when you hit the tool with a hammer, the blow drives the socket down into the fastener while the tool provides a very small amount of rotation to break the fastener lose. Though I was able to break three of the cheeseheads loose using the above tool, the rest of them refuse to come loose. I did get one to break lose using a socket turned with an 18" breaker bar, but it took a lot of torque to get the bolt to break loose. I then proceded to strip out the head on another of the bolts and decided to call it a day and have a beer before proceding any further!

In looking at the internals of the cam tower, there appears to be a golden colored"varnish" (for lack of a better term) that has everything coated. It's not very thick and I was able to scratch through it, so would guess that it is 3 to 5 thousands of an inch thick. Do you think this coating is what is making the bolts take so much torque to break loose? If so, is there a way to dissolve the coating so that I can get the bolts out easier?

Or, is it the effect of heat and time that have caused the problem?

I did find that once I broke a bolt loose, I could back it out with my fingers, so the problem is simply the contact area between the bolt and the washer under the bolt.

I'm wondering if a drop of paint remover at the interface between bolt and washer would work? Or, would the paint remover (which is caustic) attack the bearing cap material?

I'm in a holding pattern right now. I ordered a short Snapon triple square socket to improve the hold on each bolt, but really need some other way to improve the odds against stripping out any more bolt heads!

Would there be a better chance of breaking the bolts loose if I were to use an air operated impact driver?

Lastly, what is the easiest way to prevent the metal shavings produced when I drill out the stripped bolts from getting into the engine?

Ernie Rossi

RajDatta

Ernie, you must be referring to the bearing cap triple square bolts. If you are having problem removing them, I would suggest you get a 12 point 12mm craftsman shallow socket. It is just a tad bit smaller than the triple square outside head. If you hammer that on to the outside head of the riple square, it will bite it enough for you to be able to undo the bolt. I had problems with 1 of the bolts and that is what I did and it worked great.
Its extremely important to be flat and have good contact when trying to undo the bearing cap bolts. As you said, they are easy to strip. Its much easier than drilling and breaking the head off though. No metal shavings to worry about either.
The coating you are referring to seems normal from oil residue that coats engine internals over the years. Different oil types will leave a different residue. Mobil 1 oil tends to give a tan took to all the internals. The internals on my engine had a much darker tint to them and had the same coating. Its totally normal.
Raj

rdhayward

See, now you're getting me all shaky about trying this job! Couldn't you use a vise-grip instead of hammering on a socket?

RajDatta

Its light taps and believe me, I don't believe in butcher methods. If you get a good grip on the triple square heads, you don't need to worry about it. Of all times I have removed cam bearing caps, this is the 1st time something stripped so I have had good luck.
Since the caps were removed by the previous owners mechanic (belt failure, new intake cam), chances are the triple square head was somewhat mangled.
If the caps are being removed for the 1st time, I don't expect any issues. They are only torqued to 21-22lbs/ft if I remember correctly.
The trick is to have the right tool. I wouldn't let this one instance discourage you from doing this.
Raj

earossi

Raj,

Thanks for the two replies. Using a 12mm to go around the OD of the bolt head is really novel. One question: what size socket should I purchase? 3/8 or 1/2 inch? My breaker bar is a 1/2" or if I go with a 3/8' drive, I'll have to use one of my rachets with a slip over cheater.

And, to the prior poster, this is really a straight forward job. A lot of steps, but I reallly think getting the bolts to break loose is the toughest part! I'll give Raj's idea a whirl tomorrow and let you know. I really dread having to drill out any of the bolt heads.

RajDatta

3/8th.
Trust me, its not that bad and you don't have to worry about metal residue from drilling.

As they say, a picture is worth a thousand words. Here is two thousand words worth of pictures




Raj

earossi

Thanks Raj. You're right about one or two pictures saying it all. I'll give the trick a try tomorrow night or on Thursday.

Thanks again.

Ernie

earossi

Raj,

Your trick of using a 12mm socket over the head of the cap screw was great! I was able to break loose 3 of the 4 bolts I had stripped out. However, I was unsuccessful on the last one! In the end, the 12mm socket rounded off the head of the bolt.

So, what would you suggest? Is there a slightly smaller socket that I could use to attempt to repeat the process (now that the bolt head has been rounded off by the 12mm socket), or should I just resort to drilling out the bolt head?

The bolt material does not appear to be hardened since it deforms so easilly; so, could I use a chisle to break off the head?

Thanks.

Ernie

RajDatta

Ernie, have you looked at 12 point SAE sockets? There might be one that would fit the bill. Using a chisel is not something I have done so I can't say much about it. Its really upto the person on how comfortable they feel doing it.
Another suggestion would be to get a lot of masking tape and paper and cover the entire area and then try to drill.
I am glad to hear it worked on 3 of the 4.
Raj

Jfrahm

Sears has a set of bolt extractors that work quite well if there is any head to grip:

http://www.sears.com/shc/s/p_10153_12605_00952166000P

earossi

Joel,

Thanks for the suggestion of the Sears bolt extractors. I had not seen this tool. I will swing by Sears to get a closer look. There is definitely a clearance problem since the bolt is right up against a shoulder on the bearing cap. But, it is worth a look.

Thanks again.

Ewok

If you want to drill the bolt, hold a magnet next to it to catch all the metal debris.

earossi

Success at last! Well, I finally succeeded in breaking loose all 20 cam carrier bearing cap bolts. Did not have to drill any out, either. For those that have not attempted this yet, here are "my" lessons learned:

1. Your triple square socket absolutely must remain square to the bolt that you are attempting to break loose. And, your breaker bar must be peerfectly perpendicular to the socket. If the tool is tilted at all, you will strip out the bolt, as I managed to do seven times! Do not use a long triple square socket. Instead get the shortest socket you can find. Since I was desperate, I bought the Snap-on socket; however, I still managed to strip out (7) out of (20) bolts with the Snap-on.
2. If you do not believe #1, take a close look at the bolt head. The heads are about half the heighth of standard socket head cap screws. The serrations on the inside diameter of the bolt head are only partial length, so to the naked eye it looks like the total length of the serrations that engage the triple square socket are less than 1/4". That's not much bearing surface if you at attempting to put 40 to 50 ft-lbs of torque into breaking the bolts loose.
3. Although the installation of new bolts calls for about 15 ft-lbs of torque, it took 4 to 5 times that amount of torque to break the bolts loose. My engine has about 90K miles on it, and this appears to be the first time these bolts have been removed.
4. The triple sqaure bolts do not appear to be hardened, but are rather "soft" which makes stripping them very easy. They are probably designed to be soft so that they can take the stretch that will occur when the light alloy parts they are joining heat up and expand. The coefficient of expansion for alloy is much greater than the steel bolt material, which means that alloy will expand, when heated, more than the steel bolts; so, the bolts will be forced to stretch every time the engine is heated up. I would not advise replacing the bolts with bolts of a material that is hardened, or you may begin to experience bolt failures over time, since the hardened bolts will be less ductile than the soft ones. Without ductility, you could begin to see stress fractures in the bolts over time, which would not be good since the bolt will then break. I believe that is the reason Porsche designed the bolting to be ductile (soft).
5. Raj's ingenious trick of using a 12 point 12mm Sears socket to grab the outside diameter of any bolts that had been stripped out worked like a champ. Of the 20 bolts that required removal, I managed to strip out (7) of them. Six of the seven were fairly easy to remove by lightly hammering the 12mm socket around the head of the bolt and then using the breaker bar to break the bolt loose. Again, you must be ABSOLUTELY square with the bolt you are attempting to remove, or you can round off the ouside diameter of the bolt. For the single bolt that I managed to do that to, I was faced with drilling out the bolt; but, in one last desparate move, is used the rounded end of my small ball pein hammer to tap on the head of the bolt. This caused the soft bolt head to mushroom out just enough to allow me to force fit the 12 mm socket once again. I was very careful to keep the socket and the breaker bar square with the bolt, and the bolt broke loose. If that failed, I proabably would have drilled out the bolt head.
6. Since the bolt material is soft and ductile, I suspect that it should be relative easy to drill out the head, though I was spared the "opportunity" to have to do that this time around.
7. If you don't like the idea of drilling out the head, I suspect that you could use a Dremel tool fitted with a 1-1/2 inch cutoff wheel to slice the head off from the side. Since there is a rather thick aluminum washer below each bolt, you should be able to slice off the head without hitting the bearing cap. Instead, you will damage the crush washers, which is ok since you need to discard them anyway.

So, not such a bad deal afterall. My thanks to Raj for his Yankee ingenuity! Hopefully, the rest of job will go more easilly. Keep your fingers crossed!

Ernie

RajDatta

Ernie, thanks for the kind words. We sometimes tend to forget that some of these heads have 2 sides to them. If we strip one, we can still use the other.
I am glad it all worked out for you. Looks like our projects are running parallel at this point .
regards.
Raj

earossi

Well, this job is dragging on. Not because I had many problems, but because I have not been able to spend much wrenching time in the last couple of weeks.

But, I am making progress. Until this morning, I thought that I had managed to break loose all the tough bolts (cam carrier and cam sprocket). But, I have now hit a new one that isn't talked about in any of the articles I have been able to pull up.

I am at the stage where I need to pull the tensioner from the engine. I managed to get the tensioner loose and there is now slop between the tensioner piston and the pivot fulcrum. Which is where I am at a standstill. I was trying to break loose the nut that secures the fulcrum to the pivot post and I was able to get the socket to move......but, it is not the nut that is spinning.....so it must be the pivot post. I am concerned that I may have stripped threads in the block (worse case), or the pivot post is threading its way out of the block. So, what advice can anyone provide? I have a new post to install since there has been concern about these pivot posts failing in running engines.

Help would be appreciated.

Ernie