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camshaft sprocket bolt ALH/1Z/AHU engine torque spec

24698 Views 6 Replies 6 Participants Last post by  Franko6
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.
  • 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.
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Thanks. Assuming that all of what you typed is true about the end being strong enough to withstand higher forces, that's a good idea.
Good info. Despite the critics on tdiclub, it makes good sense. Even though DBW's is so strongly against this thing for whatever reason he's not perfect either. He said in one of his writeups to use the camshaft lock with the injection pump lock to counterhold the engine....that's bad advice because while I'm sure the IP lock can hold the sprocket against the beefy bracket, the camshaft lock is fragile and shouldn't be torqued on, I don't think many have picked up on it, it's in the articles section on the a3/b4 timing belt writeup. IMO, lots of complaints regarding the pdf format there and lack of updates, I prefer the format here but sorry, the forums there are still much bigger and have more info.

As for the increase in torque, it's free, it's safe, and it can only help. The consequences of that slipping would be a totaled car for many since I don't think most people want to deal with bent valves, have a spare car to drive in the meantime, etc....at least used car prices are still good!
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Are you saying that I should go back and retorque this bolt? Do you have to reset timing with the locks, etc.?
Are you saying that I should go back and retorque this bolt? Do you have to reset timing with the locks, etc.?
If it's been like that for a while I would leave it be but it's up to you. You do not need the timing belt tools to tighen this bolt since you don't loosen any sprockets. You only need to counterhold the sprocket to avoid putting stress on the timing belt while you tighten the bolt. In addition, I would put the car in neutral so that in case you do end up turning the belt that you don't put stress on a few teeth. Only if it was recently done or just done would I adjust this.
great info, it's not something that you think about but I can see how a used bolt would need a different torque than a new bolt.
I see that the argument that I started probably 15+ years ago, still goes on, about the torque spec for the ALH cam sprocket. I know I made some well known 'gurus' upset to claim 33 ft lbs on a cam sprocket was blatantly wrong, and as simply as I can put it, the claims of 'damaging the cam, sprocket or cam sprocket bolt by 'over-tightening',' is BUNK!
And I think I can speak with authority, as I know of nobody else who has built as many or of the quality I make cylinder heads for the TDI's.

Now, I see the error is being retro'ed to the AHU timing belt procedure. The AHU sprocket bolt, in several different manuals calls out a 54 ft lb torque for the cam sprocket bolt. The next cam, the ALH, is virtually IDENTICAL, and the book says 33 ft lb torque spec. The next generation, although the cam originally is cast steel, the connection id virtually identical, the sprocket material is the same and the torque for the PD motors went UP to 74 ft lbs.

In all the business I have done rebuilding TDI cylinder heads, the most avoidable is the slipping of a sprocket on an ALH, and now I find, the AHU is included with this insufficient tightening of the cam sprocket bolt. There are years that up to 6% of my cylinder head business is DIRECTLY ATTRIBUTABLE to this completely avoidable error.

Just to prove the point about damaging the cam sprocket, bolt or the cam from over-torque, I took some scrap parts, clamped the cam into a vice and tightened the sprocket bolt onto the sprocket with150ft lbs torque. I was afraid I might snap the bolt, so I stopped there. After returning from my usual Sunday morning, I pulled the sprocket bolt and used the sprocket buster to remove the sprocket and although I won't deny, it took a lot of effort and it came off with a BANG!, I could find no issues or 'damage'.

I continue to get the occasional 'spun cam sprocket', and if I could get a consensus to STOP WITH THE 33 FT LBS, I'd do it. Does it bring me business? You betcha. I'd rather not see it.

You tell me... with two of the engines; ALH and AHU, there is nearly a 20 ft lbs discrepancy in torque load. Add yet another 20 ft lbs, that's what the PD engines use. You have to use some common sense, WHY would the ALH be so different? IT'S NOT! Good Grief, it's a 14mm bolt! If it only needed 33 ft lbs, Shouldn't VAG have used a 10mm bolt??

Save yourself the heartache and expense. I use a torque spec of 45 ft lbs. And only did that to avoid the people freaking out. It should be the same as the AHU... 54 ft lbs. Do that for the AHU and ALH cam sprocket and you will not be sorry.

Frank Irving,
Frank's VW TDI's
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