Engine timing after VANOS rebuild

[gabylonfive]

Hey all, hope you're doing well and staying safe. Hoping I can get some feedback here.

I'm buttoning up my VANOS rebuild and am having an issue getting everything timed perfectly (since I have the luxury of time with shelter-in-place orders, I'm hoping to get my timing as perfect as possible even though I know the DME can compensate a bit if things are off.)

Quick summary - 170k on the motor, full Beisan suite of upgrades (hub, disc, seals, rattle kit, chain guide), S62 diaphragm springs, OEM timing tool.

The problem: I'm following the Beisan guide to the T - pistons fully retracted, cams at TDC, lock pin installed. I get the Vanos 5mm to the head and snug the 4 hub bolts down, loosen 90* then run the VANOS all the way in. Timing still looks good at that point, however when I turn the motor over a few times and recheck the timing pin won't go in smoothly, I need to nudge the cams over (advance them a bit, not retard) before it drops in. The extra weird thing is when I try loosening all the hub bolts and readjust the cams per the Beisan guide, the timing is even more off than before after tightening everything down and cranking the motor.

Any tips to try and get this right? I've tried maybe 5 times at this point and always seem to be a bit off - any tricks to the preloading sequence? should I just chalk it up to a stretched chain or something and live with it?

Thanks in advance for the help.

[robgill]

This is common. The timing can drift after a couple of rotations for a lot reasons. If it’s consistent, just cheat when you are setting the timing and compensate for the distance you know it will drift. Then after a few rotations of the motor the timing with be correct.

Another tip is you only need to tighten down and couple of hub bolts to rotate the motor and check timing. This way you only have to loosen a few bolts to make a correction. Once you can rotate the motor and timing is correct, lock them all down.

[yhp2009]

I did this last year and I do remember this being the tricky portion.
There is some "slack" between the hub and the cams when you are tightening the bolts down as a final step. It results in an ever-so slight rotation of the cams when you are buttoning everything down.

The difference in the cam timing as a result can be noticed when you try the timing bridge pin test. But rest assured that the difference is usually minuscule and the car's computer will adjust without any issues.

But one thing I did to get it perfect was that I continuously performed the timing bridge test as I was tightening down the hub and vanos bolts. This meant that everytime i turn a single bolt a full rotation, I perform the pin test.
And if its a bit off, then I used the cam wrench to adjust accordingly. I kept doing this until all the bolts were tightened to spec

Hope that helps

[beefaroni]

I ran into a similar issue. I resolved it by keeping the timing chain taut between the cam sprockets and crank by pre-loading it while verifying the crank timing mark was still in place and torquing the sprocket hardware. You only want slack on the left side of the chain where the tensioner is

[gabylonfive]

This is common. The timing can drift after a couple of rotations for a lot reasons. If it’s consistent, just cheat when you are setting the timing and compensate for the distance you know it will drift. Then after a few rotations of the motor the timing with be correct.

Another tip is you only need to tighten down and couple of hub bolts to rotate the motor and check timing. This way you only have to loosen a few bolts to make a correction. Once you can rotate the motor and timing is correct, lock them all down.

cool, at least I know I'm not going crazy and that this is more common than I thought. It appears to be consistent that the cams are a little retarded once I turn the motor a few times, so I can try setting them up advanced just a touch and see if that resolves it. Thanks for the tip!

[gabylonfive]

I ran into a similar issue. I resolved it by keeping the timing chain taut between the cam sprockets and crank by pre-loading it while verifying the crank timing mark was still in place and torquing the sprocket hardware. You only want slack on the left side of the chain where the tensioner is

interesting - so you manually tensioned the chain while tightening the hubs down? I know you only want slack on the exhaust side of the chain, but it hadn't dawned on me to help the tensioner out to pick up the rest of the slack. I installed a new tensioner as the 170k miles on the original made it feel pretty tired - but I guess there's still a bit of excess slack left. How/where exactly did you tension the chain? Just press down between the sprockets?

[beefaroni]

interesting - so you manually tensioned the chain while tightening the hubs down? I know you only want slack on the exhaust side of the chain, but it hadn't dawned on me to help the tensioner out to pick up the rest of the slack. I installed a new tensioner as the 170k miles on the original made it feel pretty tired - but I guess there's still a bit of excess slack left. How/where exactly did you tension the chain? Just press down between the sprockets?

Now I remember exactly what I did. I set the timing mark on the crank just a very tiny bit counter clockwise of the TDC mark. The crank locking pin will fit in the hole with a little bit of slop either way so I biased the clearance so the mark was just barely BTDC. Once the cams sprocket hardware is torqued down remove the crank locking pin And rotate the engine you should find that the cam timing is spot in and that little bit of slack In the chain you were compensating for was the issue.

[gabylonfive]

I did this last year and I do remember this being the tricky portion.
There is some "slack" between the hub and the cams when you are tightening the bolts down as a final step. It results in an ever-so slight rotation of the cams when you are buttoning everything down.

The difference in the cam timing as a result can be noticed when you try the timing bridge pin test. But rest assured that the difference is usually minuscule and the car's computer will adjust without any issues.

But one thing I did to get it perfect was that I continuously performed the timing bridge test as I was tightening down the hub and vanos bolts. This meant that everytime i turn a single bolt a full rotation, I perform the pin test.
And if its a bit off, then I used the cam wrench to adjust accordingly. I kept doing this until all the bolts were tightened to spec

Hope that helps

closing the loop on this - this tip solved it for me. i initially tried guessing how much slack I needed to make up by advancing the cams a bit before tightening everything down. while better, it still wasn't perfect after 5-6 rotations - I'd still need to nudge the cams over to get the pin in smoothly.

then it occured to me that maybe 90* was too much to back off if there was additional slack on a motor with 170k miles. So I retimed everything normally, backed off the hubs about 45* instead, and continually dropped the pin in to feel for cam movement and adjusted the hub bolt torque and cams accordingly. after 20 rotations, the pin drops in perfectly, no drag, no tension. 😁

thanks again for the help!

[yhp2009]

Awesome! 🤘

[Dash1]

Beefaroni is spot on. The slack in the timing chain between both hubs is what throws it off when you crank and recheck the timing - you need to add tension.

[sapote]

then it occured to me that maybe 90* was too much to back off if there was additional slack on a motor with 170k miles. So I retimed everything normally, backed off the hubs about 45* instead,

I don't see why back out the bolts 45* instead of 90* solved your problem here. The tighter the bolts the more resistance for the hubs to be rotated ccw when bolting up the vanos to the head. In fact if the bolts were tight enough the cams would rotate ccw instead of the hubs. 45* or 90* has nothing to do with 170K miles slack chain or anything else.

Did you ever turn the crank ccw when trying to set its TDC, as Beisan instruction says? Doing so can cause chain slack on the pulling side (LH viewed by driver) which leads to your retarded cams issue. Btw, even if your 170k miles chain stressed a bit, the timing process should cancel this as far as timing concern.

Did you leave the bridge pin in the cam while bolting up the vanos to the head? This can bend the pin and it became useless for checking.

As long as the crank only turned cw, then there is no chain slack from crank to the two cam sprockets.

[gabylonfive]

I don't see why back out the bolts 45* instead of 90* solved your problem here. The tighter the bolts the more resistance for the hubs to be rotated ccw when bolting up the vanos to the head. In fact if the bolts were tight enough the cams would rotate ccw instead of the hubs. 45* or 90* has nothing to do with 170K miles slack chain or anything else.

Did you ever turn the crank ccw when trying to set its TDC, as Beisan instruction says? Doing so can cause chain slack on the pulling side (LH viewed by driver) which leads to your retarded cams issue. Btw, even if your 170k miles chain stressed a bit, the timing process should cancel this as far as timing concern.

Did you leave the bridge pin in the cam while bolting up the vanos to the head? This can bend the pin and it became useless for checking.

As long as the crank only turned cw, then there is no chain slack from crank to the two cam sprockets.

I based my theory predominantly off the information on this thread: https://nam3forum.com/forums/forum/m...os-info-thread

Mainly this section regarding the preloading step:

The internal (3) Diaphragm Spring Set is designed to buffer the pressure actuation of the VANOS unit. There is a friction coefficient between the teeth of the spline shaft and hubs that must be overcome before the cams will adjust. Until this friction is overcome the pressure exerted from the pistons is basically pushing the hub assemblies into the camshafts, against the diaphragm springs (reference view (2)). Naturally, when this friction is overcome the hubs sort of spring back to their initial position, the spline shafts move freely, and subsequently adjusts the cam angles.

The ultimate goal of the "Timing Procedure" is to pre-load the (3) Diaphragm Spring Set, and to a lesser degree, remove slack from the chain link/sprocket teeth interface. If not done correctly the combination of all the slack (chain, spline teeth lash, diaphragm springs) will lead to cams that will drift out of position due to the pressure exerted by the valve springs, as the assembly is rotated.

In order to accomplish this during installation the VANOS unit is partially installed, with the spline shafts [freely] rotating the unclamped hubs. The purpose of the plastic spacers is to set the initial pre-loading distance between the cylinder head and VANOS mating surfaces. At this point the two adjacent hub bolts are torqued and loosened 1/4 turn to provide a very light hub-to-sprocket clamping force.

As you continue tightening the VANOS unit bolts, you're essentially applying pressure to the diaphragm springs, just as if the pistons and spline shafts were acting against them during normal operations (explained above).

My main goal was to remove as many variables (there are many) during this step as possible - OE timing tool, OE locking pin, OE 6mm VANOS spacers. I did not leave the timing pin in the bridge while bolting the VANOS up specifically because I knew it might get bent, I kept it out and rechecked the cams every few bolt turns. I also did not turn the crank CCW since I figured that would slacken the chain a tad, as you mentioned.

I guess the most ambiguous part of the procedure is where you tighten the 4 hub bolts up and back them off a quarter turn. "Tighten" is not a torque value and I believe the window between too loose (where the diaphragm springs are not preloaded properly) and too tight (where the cams start turning when the VANOS is drawn in) is pretty small - I found a thread on the UK boards with a TIS reference to 10nm as a torque value before loosening 90* but since i didn't have the crow's foot tool, it was a moot point anyway. Maybe I wasn't preloading the springs enough the entire time and backing it off less brought me back to the right value in the end. Dropping the pin in every few turns while the VANOS was drawn in was a good test to verify I was within that window since after a couple of turns if I felt any sort of tension, I could back the bolts off a hair and still be in time.

In the end there is probably more than one way to get this right, this is just what worked for me. It made me feel better to be able to use all the factory timing marks and not have to guess to compensate for the drift (which I'm sure I could have gotten right eventually.) Hope this proves useful to folks in the future since it appears I'm not the only one that found it a little tricky.

[sapote]

"The internal (3) Diaphragm Spring Set is designed to buffer the pressure actuation of the VANOS unit. There is a friction coefficient between the teeth of the spline shaft and hubs that must be overcome before the cams will adjust. Until this friction is overcome the pressure exerted from the pistons is basically pushing the hub assemblies into the camshafts, against the diaphragm springs (reference view (2)). Naturally, when this friction is overcome the hubs sort of spring back to their initial position, the spline shafts move freely, and subsequently adjusts the cam angles."

What is the purpose of the diaphrgm spring again? To buffer the pressure actuation of the vanos unit? I can't understand this.

The purpose of the diaphram spring is to avoid free play between the sprocket and the cam sleeve, period. In a close loop feedback system such as the vanos, any free play from the piston to the cam sleeve would lead to rattling (i.e the radial bearing has no axial play on the spline shaft). Because the sprocket rotes relative to the cam sleeve and so there is a finite clearance, and the strong compressed diaphragm eliminates the clearance to avoid rattling. IOW, if the factory could machine the parts to have zero clearance between sprocket (hub bolted up) to cam then there no need for the diaphragm spring.

The whole purpose of pretension the hub with 2 bolts (or more bolts if you like and hurt nothing) is to minimize the said clearance but still able to rotate the hub relative to sprocket. Too much clearance at this point would lead to timing shifted as the hub bolts torqued down (cam turned CCW as the hub moved rear ward millimeters) in the final step.

Btw, OE 6mm VANOS spacers is not important to have; just roughly provide 5mm or more gap is more than enough for rotating the hub CCW during the steps.

[eacmen]

Similar to previous post I always put a long dowel/screwdriver in each of the cam alignment holes, *without* the alignment bridge, while bolting the vanos to the head. This allowed me to much more easily see if the cams were moving during that process.


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