04-02-2007, 06:11 PM
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FIXING MY BABY - OEM REPAIRS
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OEM REPAIR & TECHNICAL (not modifications)
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Engine Management
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Varicam disassembly
Varicam disassembly
04-02-2007, 07:18 PM
I compressed mine by hand. You should only need the air pressure to simulate oil pressure when setting the timing.
04-02-2007, 07:41 PM
from memory, its spring pressure that acts on the 2 slippers to keep the chain tensioned and oil pressure/ solenoid is used to move the assembly up and down to change the timing. Air pressure isn't needed for disassembly and there is no pressurised oil when the engine is not running. (I pulled the head about 3 months ago but had access to the special tool)
The special tool screws into the #2 and 3 spark plug holes and holds the camshafts down while you remove the bearing saddles. I was told by OPC mech that you can do it without the tool if you progressively loosen the saddles. The thing is that while the chain is tensioned, its trying to pull the camshafts together and the saddles have a retaining spiggot that maintains their alignment. The saddles need to be removed vertically and as soon as they are off the camshaft will want to climb out of their locations in the head. The camshafts run directly in the head - there is no seperate bearing shell so you need to take care with there surfaces.
If I was doing it without the tool, I'd first remove the capscrews holding the tensioner to the head. I'd then do one side (camshaft) first undoing them progressively and evenly, gently easing the camshaft up as the saddle pressure comes off. Once the saddles are all off and the camshaft has lifted out of the head, there will be no pressure on the other shaft so it can be removed without fuss.
Others may be able to offer their experiences
The special tool screws into the #2 and 3 spark plug holes and holds the camshafts down while you remove the bearing saddles. I was told by OPC mech that you can do it without the tool if you progressively loosen the saddles. The thing is that while the chain is tensioned, its trying to pull the camshafts together and the saddles have a retaining spiggot that maintains their alignment. The saddles need to be removed vertically and as soon as they are off the camshaft will want to climb out of their locations in the head. The camshafts run directly in the head - there is no seperate bearing shell so you need to take care with there surfaces.
If I was doing it without the tool, I'd first remove the capscrews holding the tensioner to the head. I'd then do one side (camshaft) first undoing them progressively and evenly, gently easing the camshaft up as the saddle pressure comes off. Once the saddles are all off and the camshaft has lifted out of the head, there will be no pressure on the other shaft so it can be removed without fuss.
Others may be able to offer their experiences
04-02-2007, 08:32 PM
I just got thru changing the variocam chain & sliders on my 968, and all you have to do to depressurize the variocam unit is to loosen & then remove the oil feed tube. After you remove the tube you can push down on the top of the chain over the variocam slider and the oil feed check valve will pop out of the variocam body (it is located under the flange of the oil feed tube, so when the tube is removed there isn't anything to prevent it from coming out when back pressure is applied to it by compressing the variocam sliders).
Removing the variocam assembly and cams out of the head is a bit more complicated. the Porsche manual talks about using a tool that looks like a bent piece of 1/8" dia wire to hold the slider blocks in a compressed state, but it costs about $70 from Sunset Porsche which has to be ordered from Germany (over a month to get it from what they told me). I ended up using aircraft safety wire that I ran down thru the chain links on both the upper & lower side of the chain on both ends of the sliders, and then twisted the wire with aircraft safety pliers while comprssing the variocam sliders as best as I could. This released the tension on the cams just enough to keep the chain from pulling the cams towards each other and enabled me to remove the bearing caps and pull the entire variocam assembly with both cams out of the head (this avoids the need for the special bearing saddle tool that is mentioned in the Porsche factory service manual as well). I used the same method with the safety wire to reinstall the assembly into the head after replacing the chain & slider blocks, but it was very difficult to get the variocam unit into the chain & cams since it needs to be pre-compressed. I used a C-clamp with small pieces of steel plate to do this, but in the future I would do it differently by making a special tool cut out of steel plate that compresses the top slider mount ears towards the variocam body as two bolts are tightened down that go thru holes drilled in the tool and that are threaded into the upper guide pin holes. The bottom slider could then just be compressed by hand as you slide the variocam assembly into the chain & cams as a unit. Once you attempt to do all of this you will understand what I am basically talking about.
As for the special tool #9529 and using 3 bar (45 psig) air, that is for setting the timing on the cams after you have reinstalled the cams with the variocam assembly back into the head and the head is on the engine. I made a custom tool do do this by cutting out a small piece of 1/4" steel plate the same shape as the oil feed tube flange that bolts to the variocam assembly (I drilled three holes in it that matched the mounting bolt pattern and had a hole in the center where the oil feed hole is), and then welded a short piece of 1/4" steel pipe with threads on one end to it centered over the oil feed hole. I then screwed a 45 deg 1/4" pipe elbow fitting onto the threaded nipple that was welded on the above plate I made, and then screwed on a quick disconnect air chuck nipple so that I could connect my air hose up to it. This special custom tool is then bolted onto the variocam assembly and then 45 psig air pressure can be sent to it for timing the cams. There are also two dial indicator gauges needed with two separate hard mount stands that you have to mount onto the head in order to hold the dial gauges in place. I made two custom 1/4" steel plates about 3" long x 3/4" wide with the required holes drilled in them with one of the holes tapped for the thread to match the dial indicator stand rod for attaching the stand mounts to the head...the other hole in each plate is to mount the plate to the head where a valve cover screw goes into it. There are also two special plunger rods that you will have to make that screw into each dial indicator so that one of them goes down thru the spark plug hole to touch the #1 piston (a 1/8" dia rod that is 8" long is perfect for this), and the other to go to the front #1 intake lifter bucket just in front of the cam lobe (a 1/8" dia rod that is 2 1/2" long with a 1" section bent at a 45 deg angle is perfect for that one). Both of the indicator rods have to have a 4-48 thread cut onto them with a die so that they can screw into the dial indicators. After you have made all of these items then you can follow the cam timing procedure that is detailed in the Porsche factory service manual. It is actually very simple after all of the special tools have been made! (of course it will take 20 times as long to make all of the tools required as it takes to set the timing correctly...but hey, you'll have all the tools you need the next time you do that variocam chain & slider replacement and also have to reset the cam timing about 10 years in the future!! Ha)
Good luck!!
Removing the variocam assembly and cams out of the head is a bit more complicated. the Porsche manual talks about using a tool that looks like a bent piece of 1/8" dia wire to hold the slider blocks in a compressed state, but it costs about $70 from Sunset Porsche which has to be ordered from Germany (over a month to get it from what they told me). I ended up using aircraft safety wire that I ran down thru the chain links on both the upper & lower side of the chain on both ends of the sliders, and then twisted the wire with aircraft safety pliers while comprssing the variocam sliders as best as I could. This released the tension on the cams just enough to keep the chain from pulling the cams towards each other and enabled me to remove the bearing caps and pull the entire variocam assembly with both cams out of the head (this avoids the need for the special bearing saddle tool that is mentioned in the Porsche factory service manual as well). I used the same method with the safety wire to reinstall the assembly into the head after replacing the chain & slider blocks, but it was very difficult to get the variocam unit into the chain & cams since it needs to be pre-compressed. I used a C-clamp with small pieces of steel plate to do this, but in the future I would do it differently by making a special tool cut out of steel plate that compresses the top slider mount ears towards the variocam body as two bolts are tightened down that go thru holes drilled in the tool and that are threaded into the upper guide pin holes. The bottom slider could then just be compressed by hand as you slide the variocam assembly into the chain & cams as a unit. Once you attempt to do all of this you will understand what I am basically talking about.
As for the special tool #9529 and using 3 bar (45 psig) air, that is for setting the timing on the cams after you have reinstalled the cams with the variocam assembly back into the head and the head is on the engine. I made a custom tool do do this by cutting out a small piece of 1/4" steel plate the same shape as the oil feed tube flange that bolts to the variocam assembly (I drilled three holes in it that matched the mounting bolt pattern and had a hole in the center where the oil feed hole is), and then welded a short piece of 1/4" steel pipe with threads on one end to it centered over the oil feed hole. I then screwed a 45 deg 1/4" pipe elbow fitting onto the threaded nipple that was welded on the above plate I made, and then screwed on a quick disconnect air chuck nipple so that I could connect my air hose up to it. This special custom tool is then bolted onto the variocam assembly and then 45 psig air pressure can be sent to it for timing the cams. There are also two dial indicator gauges needed with two separate hard mount stands that you have to mount onto the head in order to hold the dial gauges in place. I made two custom 1/4" steel plates about 3" long x 3/4" wide with the required holes drilled in them with one of the holes tapped for the thread to match the dial indicator stand rod for attaching the stand mounts to the head...the other hole in each plate is to mount the plate to the head where a valve cover screw goes into it. There are also two special plunger rods that you will have to make that screw into each dial indicator so that one of them goes down thru the spark plug hole to touch the #1 piston (a 1/8" dia rod that is 8" long is perfect for this), and the other to go to the front #1 intake lifter bucket just in front of the cam lobe (a 1/8" dia rod that is 2 1/2" long with a 1" section bent at a 45 deg angle is perfect for that one). Both of the indicator rods have to have a 4-48 thread cut onto them with a die so that they can screw into the dial indicators. After you have made all of these items then you can follow the cam timing procedure that is detailed in the Porsche factory service manual. It is actually very simple after all of the special tools have been made! (of course it will take 20 times as long to make all of the tools required as it takes to set the timing correctly...but hey, you'll have all the tools you need the next time you do that variocam chain & slider replacement and also have to reset the cam timing about 10 years in the future!! Ha)
Good luck!!
(This post was last modified: 04-02-2007, 08:42 PM by tloof.)
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