[earossi]

I would like to change out the cam timing chain and tensioner and have a few questions.



1. Do the timing chains have a master link or do I have to remove the cams in order to change out the chain/tensioner?



2. What is the best source for the tensioner, pads, and chain? Paragon lists the chain and pads, but not the tensioner.



3. Is there a need to replace the oil supply tube to the tensioner?



4. Any advice on issues to be on the lookout for. I will obviously inspect the cams while I'm at it.



Ernie

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[unknown4u]

ans 1: There is no master link.

ans 2: If you would like to renwe the tensioner as well, You have to go to the OPC.

ans 3: Inspect it, and if you hesitate replace.

ans 4: Sent me a pm for the complete document (1 mb) that is distributed on the internet.

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[NeedPorscheSpeed]

Ernie,



I completed this job three years ago on my 1992 968, and did an inspection on my 1993 model just a couple of months ago. As Ritchie said, unfortunately, you must remove the camshafts in order to replace the camshaft timing chain and tensioner pads. As to parts, I acquired all of my parts from Sunset Porsche of Oregon, a dealer that sells OEM parts for only 15% above cost. (Their phone number is (800) 346-0182.) I would recommend that you replace the spark plug seals while you are at it, as well as the valve cover gasket. (I would definitely go OEM for the gasket and seals, for some have reported leakage with the non-OEM versions.) One of the most important aspects of this job is marking the camshafts in order to retain proper timing; making copious markings will save you big headaches down the line. Also, be sure that you "wake up" the XZN (cheesehead) bolts that secure the camshafts. I stripped three of those bolts during removal, and things went downhill in a hurry, for I spent hours attempting to get the broken bolts out. I would recommend a one-piece XZN socket, such as the ones sold by Snap-On. The ones sold by Auto Zone (i.e., those that can be inserted into normal sockets) allow for too much play, which increases the likelihood of stripping a bolt. Finally, exercise extreme caution when you remove the fuel hoses from the fuel rail, for the fuel rail cracks easily when proper leverage is not applied. (Ask me how I know? Yeah, I cracked the fuel rail on my 1992 model... <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" /> Since then, however, I have utilized the "trigger-squeeze trick" and all has been fine. I learned a lot of lessons during my first plunge three years ago, to be sure.) A final note--the 968 workshop manual calls for the utilization of a special tool during the reinstallation of the hydraulic camshaft belt tensioner. Fear not, for you can work around it by employing a vise.



Here is a link to an excellent write-up: http://www.cannell.co.uk/968_Workshop_Manu...20Camshafts.pdf



Best of luck! Please keep us posted as to your progress. I hope that you have better luck than I did with my 1992 model--I discovered 5 missing teeth on the exhaust camshaft and 1 missing tooth on the intake camshaft. Fortunately, however, when I inspected the 1993 model, all was well! <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />

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[earossi]

Well, I'm well into pulling the cams out of the head to replace the cam chain and tensioner pads. The disassembly is fairly simple and straight forward and well within the capabilities (my opinion) of the weekend wrencher. The DIY article that was provided from Rennlist (attached in one of the previous threads on this posting) is excellent and makes the job a lot easier.



The first (and hopefully "only") hurdle that I have run into is a tendency to strip out the cheesehead bolts that secure the cam shaft bearing caps to the head. Time, heat cycles, and a build up of "varnish" from oil, have made is so that a relatively large amount of torque is required to break these bolts lose. I'm using an 18" breaker bar, and it appears to take 40 to 50 pounds of pull to get the bolts lose. That's about 50 to 75 foot-pounds of torque, which apparently is more than the bolts were designed for. The problem is "how" to remove the strlpped bolts.



Raj, from Rennlist, had an ingenious idea of using a 3/8 drive 12 mm Sears shallow socket to drive over the head of the stripped bolt. The bolt material is soft enough to allow you to tap this socket into place with a small ball pein hammer. Then, using the same breaker bar, I was able to get all BUT one of the bolts to break loose. Great advice that should prevent many hours of drilling out stripped bolts for others!



So, the remaining problem is "how to" get that one bolt to break loose that is stripped in the cheesehead and also on its O.D. so that using a 12mm socket is no longer an option? A recommendation would be greatly appreciated here!



Is there a smaller socket (SAE or metric) that I could repeat the process with? Or, am I now at a point where drilling out the bolt head is my only remaining option?



I would love to put some heat on the bolt head, but am concerned about fire with all the oil that coats the engine.



Would someone please provide an option short of drilling out the head of the bolt?

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[Eric_K]

These worked for me to remove a stripped flywheel bolt.



http://www.sears.com/shc/s/p_10153_12605_00952162000P

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[rustech]

If there is room to get a set of vise-grips on the head, then you could tap it with a hammer to free it. I had to do this on a carb on my old boat and it worked like a charm.

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[earossi]

Unfortunately, there is not enough room to get a good bite with vice grips. Looking at the cheeshead bolts, the bolt heads are of a shallow design, which is unfortunately. A standard socket head cap screw has almost twice the depth of this Porsche item. I'm certain that the shallow design saves a little weight, but there was probably little thought given to fastener failure when the bolts become slightly tight due to age and temperature.









[quote name='rustech' post='49827' date='Mar 26 2008, 10:35 PM']If there is room to get a set of vise-grips on the head, then you could tap it with a hammer to free it. I had to do this on a carb on my old boat and it worked like a charm.[/quote]

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[Ryan]

Have you considered using a Dremel with a cut-off wheel to cut a slot in the head? You could put ViseGrips on a screw driver and try to turn it that way.

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[earossi]

Yes, I had considered using a Dremel to cut off the head, but not to put a screwdriver slot in the head. My guess is that the bolt head is soft, and that at least one side of the head would break off when I put torque on the screwdriver. Instead, I would use a small cutoff wheel to slice the head off the bolt. Since there is a fairly thick aluminum crush washer below the bolt head, I should be able to cut off the bolt head without cutting into the actual bearing saddle.



But, I have resisted all this since I am concerned about keeping metal debris out of the engine. So, the Dremel or drilling out the bolt head are my last ditch efforts, if all else fails.



Thanks for the idea, though.



Ernie





[quote name='Ryan' post='49837' date='Mar 27 2008, 08:54 AM']Have you considered using a Dremel with a cut-off wheel to cut a slot in the head? You could put ViseGrips on a screw driver and try to turn it that way.[/quote]

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[RS Barn]

Ernie,

get a very sharp chisel and wack several times straight into the head on the outside holidng the chisel face vertically . Then angle the chisel very slightly (in the direction of loosining) and smack very smartly while holding chisel very tight. You may have to hit it 8-12 times. That usually does it.

Sometimes when really stubborn, you will need to do this again from opposite side of bolt. So pick a starting point that allows you to get two shots!!!!

Two tricks to this. You only want to angle chisel very slightly so not to chunk off a piece of bolt. It also helps to take a drift and smack bolt head after two or three angled hits to untension bolt.

Uh-I done this before

Pete

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[earossi]

--------------------------------------------------------------------------------



Pete,



Thanks for the reply. Fortunately, I have just completed the job this evening. Having now removed all 20 cam carrier bolts, I managed to stip out 7 of the 20. I have pasted in, below, my lessons learned that I just posted over on the Rennlist board. My saviour, was some Yankee ingenuity suggested by Raj over on the Rennliste site. If you take a 12mm 12 point socket, you can get it to cut into the OD of the stipped bolt head using a ball pein hammer. Since the bolt heads are very soft, driving the socket onto the bolt is very easy. Once installed (squarely), I used my breaker bar to break 6 of the 7 bolts loose. No doubt that your suggested technique would have worked also.



I have pasted in the text of my last posting on the Rennlist board that provides my "lessons learned" from the ordeal of working with these dead soft bolts. Here it is:



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 perfectly 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, I 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 relativly 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

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[earossi]

The bolts are dead soft, and were probably annealed as a portion of the manufacturing cycle (which is one reason they strip so easilly), and mine appeared to be fine when I pulled them at 90K miles; so, I think they should be good to last through the life of a chain and pads (about 100K miles). Cold, they are fairly lightly loaded, needing only 15 fot-lbs of torque. They are also set up against an aluminum crush washer, which should crush if the stresses get to high in the bolts. I would, however, suggest that you replace every one of them when you pull the caps. They were pretty cheap.



If I were going to get serious about it, I would look for socket head cap screws with a deeper socket made out of annealed steel. But, I think that the Porsche design is OK if you accept the fact that you will probably strip a few every time you remove the cam carrier caps.















[quote name='rdhayward' post='49900' date='Mar 28 2008, 05:51 AM']Does anyone think it advisable to replace these bolts periodically? I frequently replace headbolts due to the perception that they stretch and/or become britle over time.



One more question: can you use break cleaner or similar solvent to clean the varnish from the galley (top of the head)?[/quote]

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[RS Barn]

I only use Snap On tool. It is short and very hard-very little flex.

I first insert the 12 point and give it a wack with a hammer to shock the bolt.

I use a long flex head 3/8 wratchet (snap on) and put lots of pressure down on the head.

This puts all the torque on the bolt. Usually 90% break loose

My chisel technique works for the rest. I've done 100 or so to date and haven't needed to use sockets.

Pete

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[earossi]

Pete,



You wrote that you use a flex head socket wrench. I assume that you find that it works better than a standard rachet. Do you feel that the flex head allows you better align the wrench with the bolt head? Just curious.



Ernie









[quote name='RS Barn' post='49970' date='Mar 28 2008, 09:59 PM']I only use Snap On tool. It is short and very hard-very little flex.

I first insert the 12 point and give it a wack with a hammer to shock the bolt.

I use a long flex head 3/8 wratchet (snap on) and put lots of pressure down on the head.

This puts all the torque on the bolt. Usually 90% break loose

My chisel technique works for the rest. I've done 100 or so to date and haven't needed to use sockets.

Pete[/quote]

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[RS Barn]

Ernie,

When you press down hard with your left hand on ratchet head it is hard to keep absolutly right level. The flex head keeps everything square

Pete

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[earossi]

Well, on to the next issue. When I removed the little oil delivery tube that feeds oil to the Varicam actuator, there is a checck valve along with a "green cuff" under the tube's flange. When I lifted the cuff off the flange with a pair of tweezers, the cuff came apart from the check valve. I then pulled the check valve out and it seems intact and fine.



Since my understanding was that the green cuff and check valve were supposed to be a single assembly, can I assume that the cuff is broken?



Pricing forf the checkvalve and cuff was $200 with 12 days delivery from Germany!!! There has got to be a better solution to this little part.



Any assistance would be appreciated.



Ernie

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[earossi]

When you removed the O-ring and check valve, did they come out as a single assembly or as an O-ring (attached to the green cuff) and a separate check valve? That's my issue.









[quote name='rdhayward' post='50653' date='Apr 8 2008, 09:54 PM']I thought it was just a little O-ring, and I'd bet you could replace it by going to a parts store and fishing through their AC line O-rings.



Also, I want to say that the advice (given in one DIY write-up) to remove that item is a bit misplaced. I saw no reason whatsoever to have removed it after I did so and realized it was just a crude check valve. Leave it alone!



Good luck![/quote]

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[earossi]

Well, I have it all apart now. Cam sprockets look OK. I have changed the pads out on the varicam. Both upper and lower pads that I took off looked terrible. Not broken, but score marks (worse in the lower pad, but not by much!) were about .020" deep.



One last hurdle and everything should go together. I'm trying to assemble the chain on the cams and at the same time both compress the chain tensioner and slip it between the cams. You need three sets of hands to do this. Though I have a vice and can compress the tentioner ok, there is no way (short of the special 9280 tool to hold the tensioner in its compressed state.



So, how can I either fab the tool that indexes into the holes located in the new pads, or get my hands on one? I tried fashioning one out of some thick wire (clothes hanger wire), but the wire is so soft that it bends as soon as I release pressure on the compressed actuator.



Thanks in advance.



Ernie

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[rob76turbo]

Ernie,



We recently used some of the spool wire from Home Depot and it is much stronger than a wire hanger. We used this to compress some rear shocks on my friends car. YOu may want to try that.

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[earossi]

[quote name='rob76turbo' post='50898' date='Apr 14 2008, 05:09 PM']Ernie,



We recently used some of the spool wire from Home Depot and it is much stronger than a wire hanger. We used this to compress some rear shocks on my friends car. YOu may want to try that.[/quote]





Thanks for the suggestion. Ironicallly, one of my local gear heads suggested the same thing, so I stopped at Home Depot on the way home tonight and bought some of the 1/8" rod. It looks much stouter than coat hanger.



Incidentally, I checked with Sunset Porsche this morning to get pricing and availability on the Porsche tool for this purpose. Pete at RS Barn was kind enough to take the time to provide the tools proper part number. That was the good news. Sunset did a national check, and there is not one copy of the tool at any USA dealer. And, the factory (Germany) shows that they are back ordered on the part. Cost would have been $37 and you get the actuator retainer plus a tool to insert in the timing belt tensioner to hold it in the compressed condition. Would have been nice to have both, but I was able to use a nail in the tensioner.



Thanks again for the suggestion.



Ernie

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