S54 Vanos post Beisan/DV Rebuild Timing Issue

[sapote]

For those that have the timing bridge that off the head on the intake side after complete the VANOS timing procedure, I believe this is mostly due to the chain slack. For whatever the reason BMW instruction doesn’t ask to use a solid chain tension as it is required when doing the timing on non-M cars. As soon as the hubs bolts were released, the sprockets are free to turn and causing chain slack on the pulling side (RH side front view) which leads to the timing small error.

We have 2 choices to correct this: install a hard chain tensioner tool (I used a socket instead of the stock spring loaded piston), or offset the crank pulley 2mm CCW from TDC.
For those that have the timing bridge that off the head on the intake side after complete the VANOS timing procedure, I believe this is mostly due to the chain slack. For whatever the reason BMW instruction doesn’t ask to use a solid chain tension as it is required when doing the timing on non-M cars. As soon as the hubs bolts were released, the sprockets are free to turn and causing chain slack on the pulling side (RH side front view) which leads to the timing small error.

We have 2 choices to correct this: install a hard chain tensioner tool (I used a socket instead of the stock spring loaded piston), or offset the crank pulley 2mm CCW from TDC.

[sapote]

ALL hub bolts - the 6 of them. I am sorry this is not clear, this implies the hubs are already on the sprockets, with all bolts in place but finger tight. this can be done with, or without the spline inserted, does not matter as you need to loosen all of them again to start the assembly, this is just to have visual marks for the torque settings. this works, it was tested, and you can repeatedly reach 14NM and have the marks aligned as long as you don't pull the screws out completely and inserted in another location

as for your comment above, I am sorry but you are not correct. and no, you don't have to bias the crank to achieve timing. if the preload process is done correctly it wont move. there are physical reasons for this which I bullet point bellow

• preload by tightening one bolt at a time skews the hub, which makes the spline to bin and as a result is dragged in separating the piston from the cap
• if preload is done by tightening side by side by small amounts (1/4 of a turn on this bolt is just 0.25mm of displacement), this allows the hub to rotate around the spline as it is being tighten, this wont drag the spline in

there are other potential ways around this, like torque the hubs with the splines in but out enough that they will remained bottomed out as the VNAOS unit is placed. the torque of the VANOS bolts will force it in place making the hubs to spin CCW. Not that I would do this, I told my friend not to try this even when he had been told this worked for his mechanic friend 100's of times. but hey, there are several ways to skin a cat, you pick what you feel more comfortable with.

BTW, we tried the bias approach, and the two times we did it we were off, at which point it was just more effective to do what we did (what I wrote). this sequence allowed the engine to be on time with both pins sliding easily with the bridge flat on the head.

1) Add the final torque mark on the bolts is a great idea.
2) So after pretension the hub with the 2 bolts (across from each other), the hub could move away from the cam/sprocket by 0.25mm max. This means during the final torqueing down the hub, it only can move rearward 0.25mm max and the potential of pulling the piston rearward no more than 0.25mm away from the VANOS cap. The hub cannot pull the piston more than the distance the hub actually moved, 0.25mm. So the idea that when the 2 hub bolts are not evenly torqued down -- total only 1/4 turns -- that cause the hub to pull the piston more than 0.25mm is not right. Say how could the piston moves 0.50mm off the cap if the hub only moved 0.25mm?
3) Here is what cause the final small error: the hub moved 0.25mm at the final torqueing step + the chain slack when the original hubs bolts were loosen. The amount of chain slack depends on how tight the chain tensioner is with no oil pressure. Some has more than the others depending on the oil leaking condition. The M3 vanos instruction doesn't require a special tensioner vs. the non-M cars require this special tensioner to keep the chain tight during the whole process after setting the crank and cams at timing positions. So to compensate for the error, the crank needs to be offset a few millimeter CCW from TDC.

[maupineda]

* "tighten the hubs with a torque wrench to 14NM, and add what I call torque marks"
This is unclear instruction, as the hub has no threads to be tighten.And if using bolts then how many bolts? Don't assume people will only use 2 bolts.

* "what happens is that if preload is not applied evenly, as you tighten the hub, it drags the piston into the hub effectively creating space between the piston and the VANOS unit cap"
When the hub is bolting down, for sure it will pull the piston the same amount of movement by the spline shaft. You can't expect the spline shaft somehow be able to slip through the hub and not being pulled along (it might turn instead of being pulled along, but since pulling the piston is a very light load and so I bet the spline shaft not rotate but being pulled along), no matter how EVENTLY you torque down the 2 bolts. This is the reason why one should bias the crank pulley a few mm CCW to compensate for this "pistons pulling syndrome" which causes the final timing a little retarded.

ALL hub bolts - the 6 of them. I am sorry this is not clear, this implies the hubs are already on the sprockets, with all bolts in place but finger tight. this can be done with, or without the spline inserted, does not matter as you need to loosen all of them again to start the assembly, this is just to have visual marks for the torque settings. this works, it was tested, and you can repeatedly reach 14NM and have the marks aligned as long as you don't pull the screws out completely and inserted in another location

as for your comment above, I am sorry but you are not correct. and no, you don't have to bias the crank to achieve timing. if the preload process is done correctly it wont move. there are physical reasons for this which I bullet point bellow

• preload by tightening one bolt at a time skews the hub, which makes the spline to bin and as a result is dragged in separating the piston from the cap
• if preload is done by tightening side by side by small amounts (1/4 of a turn on this bolt is just 0.25mm of displacement), this allows the hub to rotate around the spline as it is being tighten, this wont drag the spline in

there are other potential ways around this, like torque the hubs with the splines in but out enough that they will remained bottomed out as the VNAOS unit is placed. the torque of the VANOS bolts will force it in place making the hubs to spin CCW. Not that I would do this, I told my friend not to try this even when he had been told this worked for his mechanic friend 100's of times. but hey, there are several ways to skin a cat, you pick what you feel more comfortable with.

BTW, we tried the bias approach, and the two times we did it we were off, at which point it was just more effective to do what we did (what I wrote). this sequence allowed the engine to be on time with both pins sliding easily with the bridge flat on the head.

[Cubieman]

You can train an ant and place it inside then bolt down the cap and ask the ant to see if there is any gaps between the piston end and the cap, as this is the only way.
Or, this is even better: ask the ant to stand on the end of the piston, then bolt down the cap to spec, then remove the cap and see if our dear ant was flatted down to less than paper thin.

Ha, now that's what I need this in my toolbox. I just figured that once the piston reached that tapered edge that was it. But as you say not exact, I will post measurement "C" if/when I do it.

[sapote]

You are correct, I don't have a point of reference except visual from a YouTube video/my assement of what looks to be the "end point" for the pistons. I didn't perform and sort of measurement. Would be nice to know the distance measurement if someone has it.

A video or picture cannot convey 1mm or 2mm difference. A sure way is to measure the distance "C" from the cap base to the tip of the inside circular riser (it's a broken circle in order for the oil to flow through), then measure the end of piston to the vanos face and this dimension should be equal to C.

[Cubieman]

You meant as far forward as possible?
Hmm, how do you know it was as far as it can be? You have no reference to know this, or it might be 2mm short?

I meant they were as are far back into the vanos as possible. And you are correct in that I don't know for a fact that they are into the vanos as far as possible.

I watched a video linked in the Vanos Mega Thread in which the gentleman removed the caps demonstrating the correct postion of the vanos pistons and mine were dead even with the tapered portion of the cylinder shown in the photos.

If you look inside the caps there is a small circular protrusion that I *think* acts as the stop point for the pistons. So it would appear that visually my pistons were in the vanos as far as possible.

You are correct, I don't have a point of reference except visual from a YouTube video/my assement of what looks to be the "end point" for the pistons. I didn't perform and sort of measurement. Would be nice to know the distance measurement if someone has it.

[sapote]

After I was all done I removed the vanos "caps" just to make me feel better, it would appear that the pistons were as far back as possible.

You meant as far forward as possible?
Hmm, how do you know it was as far as it can be? You have no reference to know this, or it might be 2mm short? You can train an ant and place it inside then bolt down the cap and ask the ant to see if there is any gaps between the piston end and the cap, as this is the only way.
Or, this is even better: ask the ant to stand on the end of the piston, then bolt down the cap to spec, then remove the cap and see if our dear ant was flatted down to less than paper thin.

[Cubieman]

Glad to hear I am not alone. I spoke with Raj about this... He basically said this just happens to some engines, no one knows why. He said that what he has heard people do is that they do what I did and bias it. Hasn't heard of any ill effects. I have turned the engine over 20+ times doing valve adjustments, and timing is still spot on so I am satisfied.

Awesome, sounds like your good to go then! I was so very nervous, "I am timing an S54 engine and it's not going according to instructions!"
I was shaking as a turned the key the first time, no shit.
I really thought I might introduce the pistons to the valves. The forum members were quite helpful/patient, Raj told me the same thing in regards to why the biasing must be done sometimes, kind of unknown. I'm sure there's reasons, there must be, it's just probably so many things it could be it wasn't worth speculation.

[sapote]

- before putting the VANOS unit on, tighten the hubs with a torque wrench to 14NM, and add what I call torque marks... add two marks per bolt so you have two reference points, this will allow to torque the hubs much closer to the actual spec than go by feel

what happens is that if preload is not applied evenly, as you tighten the hub, it drags the piston into the hub effectively creating space between the piston and the VANOS unit cap, and it is KEY (aka A MUST) that pistons remained bottomed out into the VANOS unit for timing to be maintained, if they are pulled into the hub during preload and they no longer are bottomed out, as you spin the engine, the cams will not start rotating along with the engine until they are bottomed out again, and this is what throws your timing off, it is very minor, but enough to not let the pin on the bridge to go in fully.

* "tighten the hubs with a torque wrench to 14NM, and add what I call torque marks"
This is unclear instruction, as the hub has no threads to be tighten.And if using bolts then how many bolts? Don't assume people will only use 2 bolts.

* "what happens is that if preload is not applied evenly, as you tighten the hub, it drags the piston into the hub effectively creating space between the piston and the VANOS unit cap"
When the hub is bolting down, for sure it will pull the piston the same amount of movement by the spline shaft. You can't expect the spline shaft somehow be able to slip through the hub and not being pulled along (it might turn instead of being pulled along, but since pulling the piston is a very light load and so I bet the spline shaft not rotate but being pulled along), no matter how EVENTLY you torque down the 2 bolts. This is the reason why one should bias the crank pulley a few mm CCW to compensate for this "pistons pulling syndrome" which causes the final timing a little retarded.

[Joshb556]

Glad to hear I am not alone. I spoke with Raj about this... He basically said this just happens to some engines, no one knows why. He said that what he has heard people do is that they do what I did and bias it. Hasn't heard of any ill effects. I have turned the engine over 20+ times doing valve adjustments, and timing is still spot on so I am satisfied.

[maupineda]

they will be fine if you torque to spec, don't worry, just use a torque wrench since aluminum does not take much to be screwed over.

[Cubieman]

One thing I kept worrying about when re-installing the vanos over and over was "how many times can I thread these bolts in before I wear out the female threads/strip the threads?" " Is it OK to torque these bolts down 15 times or are they getting fatigued?"

My dad, whose garge I borrow when I work on the car said, "Jesus, you kept treating that engine like a drag car engine and your going to fuck something up", implying stop bolting/unbolting. But unfortunately that's what it takes, I'll get to do it all over soon enough if my hubs need removal, can't wait!

[maupineda]

After I was all done I removed the vanos "caps" just to make me feel better, it would appear that the pistons were as far back as possible.

I feel you, I tried to do it but on the Z4 there is no space to remove the damn caps, or not with my tool set. the issue is that it would be just a placebo, unless you can cut a section, or see through, you don't know. or maybe some paint and put the cap back on and see if there is contact. but at that point it will be easier to just start over, at the end, if the pin goes in is the confirmation you need.

[Cubieman]

After I was all done I removed the vanos "caps" just to make me feel better, it would appear that the pistons were as far back as possible.

[maupineda]

A friend and I just did a Z4M, and we did struggle and had to do the timing process 3 times (same issue as you and Cubieman), and the next is what worked well in the end, which is a slight deviation from the TIS and Beisan DIY procedure. below are the key steps you need to add into the mix. it took me a bit of wondering and brain time to understand why it was happening, and the below is the result of that thought process.

- before putting the VANOS unit on, tighten the hubs with a torque wrench to 14NM, and add what I call torque marks... add two marks per bolt so you have two reference points, this will allow to torque the hubs much closer to the actual spec than go by feel

1. - Follow the VANOS assembly procedure to the "T" up to the point where you back out the 9 & 3 o'clock bolts on each hub by 1/4 of a turn (try to be as precise with this as possible), and slowly start tightening the VANOS unit evenly, it is very important to go no more than 1/2 turn max on either side so the unit is driven straight forward onto the head for the last 5mm stretch.
2. - now, here is where we did something a bit different once the unit is fully seated onto the head
   • - using your torque marks, now tighten the 9 & 3 o'clock bolts to spec, but go even 1/4 of a turn by 1/4 of a turn, again, key is to apply preload evenly around the diameter of the hub, do one hub at a time.
   • - after reaching torque, tighten the top two bolts you can reach, but don't reach the torque marks, stay 1/4 of a turn from them
   • - spin the engine 1 full crank rotation (1 crank rotation is 1/2 a turn at the camshafts)
   • - this will expose the bottom bolts you did not see, so again, 1/4 of a turn by 1/4 of a turn tighten them evenly until your reach the torque marks
   • - spin the engine carefully as this time you will lock the engine again at TDC (if you passed the TDM mark, just spin two more rotations, don't go back as you don't want chain slack to be against you), lock the engine
   • - now drive the top two bolts to your toque marks, with this you have torqued all bolts on the hubs
3. - check timing, it should be fine

what happens is that if preload is not applied evenly, as you tighten the hub, it drags the piston into the hub effectively creating space between the piston and the VANOS unit cap, and it is KEY (aka A MUST) that pistons remained bottomed out into the VANOS unit for timing to be maintained, if they are pulled into the hub during preload and they no longer are bottomed out, as you spin the engine, the cams will not start rotating along with the engine until they are bottomed out again, and this is what throws your timing off, it is very minor, but enough to not let the pin on the bridge to go in fully.

if you screw the timing, you MUST loosen the unit, loosen the hubs, pull the unit back enough for you to use a pick to drive the pistons again into the unit until they bottom out, and start the process over.

if you do it carefully and evenly it will be right the first time, it just take patience (don't go all in on each bolt at once!), then again, the key is to drive the unit home parallel side to side and apply preload evenly so the pistons remain bottomed out into the VANOS unit during the whole process.

the only difference here is the care and sequence, the TIS and Beisan procedures have you apply preload on 3 bolts, this shifts preload to a quarter of the circumference of the hub, and all you need is the spline to be dragged in a tiny bit to make you bang your head against the wall