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I have updated the timing belt writeups for the ALH/1Z/AHU engines. This is all north american TDI engines 1996-2003. The issue is the torque spec on the camshaft sprocket bolt.
Some people report the camshaft sprocket spinning on the camshaft. This results in a loss of valve-piston timing and bent valves/damaged heads. The effect is very similar to a timing belt losing teeth and slipping. There may have been a variety of causes for this including user error, bad torque wrenches, oil or grease on the camshaft taper, or damaged threads on the bolt or camshaft. It's also been suggested that the factory torque spec is fine.
If you believe that the factory torque spec is fine then continue to use it. However, if the camshaft sprocket slips the result is severe engine damage. A slightly higher torque on the camshaft sprocket bolt will increase the clamping onto the tapered end of the camshaft and not damage anything. Because of this, I suggest a slightly higher torque value. There is a heck of a lot to lose if it slips and I believe that there is nothing to lose by going slightly tighter on this bolt.
Here is a thread on tdiclub with more info:http://forums.tdiclub.com/showthread.php?t=218960&page=2 , frank06 torqued the camshaft bolt to 150 ft lbs without any noticeable damage. Of course, this does not mean that there was no damage and that it could sustain this after being exposed to engine vibration, heat and expansion, etc., this was only a test. This also assumes an accurate torque wrench and correct gear puller to prevent any damage upon sprocket removal. Others have reported a broken camshaft at lower torque values. 35-45 ft-lbs is well within any possible damage and is a about 15% more torque. I believe that this is enough to help prevent a possible spun camshaft sprocket.
I always err on the side of caution so I have updated the torque spec info and added some notes so the reader can make up their own mind. The tips on this site are for your entertainment only and any damage resulting to persons or property as a result of the information on this site are not the liability of myturbodiesel.com. Use of this website is your agreement to these terms. Basically, you are your own warranty if you work on your car!
Below is what I added. Here is a picture of the bolt being tightened for illustraion.
CAUTION - Make sure that the tapered conical tip of the camshaft is clean and dry because damage to the threads, tapered camshaft end, or an oiled taper, can change the torque value and result in a spun camshaft sprocket and engine damage! I personally use a higher torque spec of 35-40 ft-lbs on the camshaft sprocket bolt but not higher than 45. This is only about a 15% increase in torque over the recommended factory value. The reason this caution has been added is because there have been reports of multiple spun camshaft sprockets (not mine). Regardless of the cause (faulty torque wrench, user error, etc.,), a slightly higher value on this bolt will not damage the camshaft end, sprocket, or the 12mm sprocket bolt, but will add a margin of safety against a spun sprocket. I believe that this range is a safe balance between spinning the sprocket and any possible damage to the camshaft or sprocket.
Here is a breakdown of the components so you can decide for yourself: the bolt, the camshaft threads, the camshaft taper, the sprocket, the belt position.
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Some people report the camshaft sprocket spinning on the camshaft. This results in a loss of valve-piston timing and bent valves/damaged heads. The effect is very similar to a timing belt losing teeth and slipping. There may have been a variety of causes for this including user error, bad torque wrenches, oil or grease on the camshaft taper, or damaged threads on the bolt or camshaft. It's also been suggested that the factory torque spec is fine.
If you believe that the factory torque spec is fine then continue to use it. However, if the camshaft sprocket slips the result is severe engine damage. A slightly higher torque on the camshaft sprocket bolt will increase the clamping onto the tapered end of the camshaft and not damage anything. Because of this, I suggest a slightly higher torque value. There is a heck of a lot to lose if it slips and I believe that there is nothing to lose by going slightly tighter on this bolt.
Here is a thread on tdiclub with more info:http://forums.tdiclub.com/showthread.php?t=218960&page=2 , frank06 torqued the camshaft bolt to 150 ft lbs without any noticeable damage. Of course, this does not mean that there was no damage and that it could sustain this after being exposed to engine vibration, heat and expansion, etc., this was only a test. This also assumes an accurate torque wrench and correct gear puller to prevent any damage upon sprocket removal. Others have reported a broken camshaft at lower torque values. 35-45 ft-lbs is well within any possible damage and is a about 15% more torque. I believe that this is enough to help prevent a possible spun camshaft sprocket.
I always err on the side of caution so I have updated the torque spec info and added some notes so the reader can make up their own mind. The tips on this site are for your entertainment only and any damage resulting to persons or property as a result of the information on this site are not the liability of myturbodiesel.com. Use of this website is your agreement to these terms. Basically, you are your own warranty if you work on your car!
Below is what I added. Here is a picture of the bolt being tightened for illustraion.
CAUTION - Make sure that the tapered conical tip of the camshaft is clean and dry because damage to the threads, tapered camshaft end, or an oiled taper, can change the torque value and result in a spun camshaft sprocket and engine damage! I personally use a higher torque spec of 35-40 ft-lbs on the camshaft sprocket bolt but not higher than 45. This is only about a 15% increase in torque over the recommended factory value. The reason this caution has been added is because there have been reports of multiple spun camshaft sprockets (not mine). Regardless of the cause (faulty torque wrench, user error, etc.,), a slightly higher value on this bolt will not damage the camshaft end, sprocket, or the 12mm sprocket bolt, but will add a margin of safety against a spun sprocket. I believe that this range is a safe balance between spinning the sprocket and any possible damage to the camshaft or sprocket.
Here is a breakdown of the components so you can decide for yourself: the bolt, the camshaft threads, the camshaft taper, the sprocket, the belt position.
- The camshaft sprocket bolt is large compared to the low torque value of 33 and will not be damaged by a small increase in torque value. Later BEW engines use a torque of 74 ft lbs on an identical bolt. Albeit the engine is different, the bolt is the same.
- The camshaft threads are not brittle enough to be damaged by a 15% increase, I would not go over 40 although others have tested the camshaft to well over 50 ft-lbs without any damage when using proper tools and pullers.
- The taper is also strong and it is not likely that it will be damaged or deformed by a small increase. Of course whacking the sprocket with a hammer or improper removal can cause damage so always use a puller or the method in the factory service manual.
- There have not been any reports of damage to the sprocket due to a higher torque.
- The belt position on the sprocket is not dictated by the sprocket and is unchanged.
