Cold start rattle 2-3 seconds then gone.

[BigLooga]

It either sounds like something is getting starved of oil or takes a second to settle. I would check that main tension guide. Sadly the Vanos has to come out to see it but it's probably broke. Something like a clogged filter could be stopping the Vanos from getting immediate oil pressure. Have you gotten your exhaust hub squared away or is everything still stock?

Stock Vanos for me.

Well, if that would be the case of lower oil pressure then i would probably have a vanos issue but the power at all rpm is good and there is no lag or noticable power issue. From what i read about the vanos "lockdown" by changing the hub with tigher cleareances i just don't see my issue as being a symptom of a bad hub or broken tabs. Thanks for the suggestion, i'll continue to monitor the situtation.

[sapote]

Since Vanos has never worked on, I assume the upper right chain guide is original and could be worn and broken by now. Don’t know if that broken guide can cause more loose chain at startup, but sure it cannot be tighter.

[BigLooga]

Since Vanos has never worked on, I assume the upper right chain guide is original and could be worn and broken by now. Don’t know if that broken guide can cause more loose chain at startup, but sure it cannot be tighter.

True, but then if it would be the case of a broken guide, wouldn't it make noise during all starts, not only cold. And it would probably be noisy during operation. I mean my car is not that noisy, the S54 is not really a quiet engine, i didn't really notice any other noises other than the cold start noise. Thanks for the opinion, do you know if there is a way i could check for a broken guide? Not really down to pull the pan, just did a oil change, looked at the oil and didn't find any debris and also filter didn't show any foreign objects.

Thanks.

[sapote]

Many people didn't notice any noise during running until removing the guide and found it was about 1" shorter as the bottom tip worn and fell off. With a broken bottom tip, the tension has to extend further to push the same pressure on the chain.
Cold engine: takes more time to fill the tensioner
warm engine: tensioner was partially filled and less time to fill up.

[Cmamainer]

In my case the rattle was present prior to the vanos upgrades and in fact the original vanos was in excellent condition with very little wear on the chain guides w/no visible issues. So its still unresolved to this point.

[BigLooga]

In my case the rattle was present prior to the vanos upgrades and in fact the original vanos was in excellent condition with very little wear on the chain guides w/no visible issues. So its still unresolved to this point.

Cmaminer, you have a similar problem? For me, im almost tempted to exclude vanos as the sound is more like a knocking, like a piece of metal knocking on another piece of metal, the noise follows the rpm's and i'm almost tempted to say that it sounds like its coming from the cams turning and then poof the noise disspears, litteraly 2 seconds. The vanos having a broken tab IMO does not generate this sound and if oil flow was a problem with VANOS then technically i would probably see some sort of performance variations, which i do not, the car pulls strong all rpms, no check engine or stored codes.

I'm tempted to pour some oil straight pipe into the oil cap just prior to a cold start to see if maybe it would fix it "temporarily".

Im also tempted to exclude the timing chain and guides as the knock i'm hearing i just can't see how it would be generated by a chain or a chain slapping against a piece of metal or plastic. My sound is definately some hard noise, ala hard piece of metal hitting another hard piece of metal and not a "soft" noise such as a chain "lashing" sound, hard to describe. A video would almost be perfect for this, i'll see how i could try to upload a video of my issue.

Thanks for the feedback

[Cmamainer]

I'm at a loss up to this point, It seems like oil is completely draining from the vanos after engine is shut down for awhile. I tried a new accumulator but that didn't change anything, but like yourself it runs great and pulls hard with no check engine light?

[sapote]

I'm at a loss up to this point, It seems like oil is completely draining from the vanos after engine is shut down for awhile. I tried a new accumulator but that didn't change anything, but like yourself it runs great and pulls hard with no check engine light?

What if the chain tensioner leaked the oil and took a few second to build up pressure? I don't think vanos is the issue in this case.

[Cmamainer]

I have replaced the chain tensioner with no improvement?

[sapote]

I have replaced the chain tensioner with no improvement?

Use a pressure gauge to monitor the oil pressure at the vanos banjo bolt, to see how fast it drops after engine turned off. It's good to get this out of your mind, but I doubt the vanos can cause the rattling noise of a chain at start up.

[Cmamainer]

To anyone who is still having this issue I replaced my original oil filter housing with a new one and the cold start rattle is gone.

[eacmen]

To anyone who is still having this issue I replaced my original oil filter housing with a new one and the cold start rattle is gone.

What caused you to take this action? Were you observing low oil pressure?

[Cmamainer]

No, I was in contact with a member from the old forum that went by the name "Zaharias", he was having the same exact issue and had rebuilt the vanos like I had and changed the rod bearings with no improvement. His mechanic recommended changing the oil filter housing believing that it was allowing oil to drain from the topend while sitting for extended periods such as overnight and it seems he was correct.

[sapote]

To anyone who is still having this issue I replaced my original oil filter housing with a new one and the cold start rattle is gone.

Makes sense if the engine oil was drained due to the plastic check valve cut a slot on the OFH.

[WestBankM4]

I'm having these exact same symptoms, funnily enough, it only started happening AFTER I completed my top end rebuild. It has been making a rattling, knock sort of noise for 1-2 seconds upon a cold start, it's always in the morning when the car has sat overnight. Vanos has been upgraded to Beisan and had less than 500 miles on it at the time, so I knew it wasn't that but I too searched high and low for the source. Sounds like you found the culprit for me, I appreciate you updating this thread. Going to order an OEM piece and get to work, most likely upgrade the pulleys since I'll be in that general area anyway.