Vanos Timing Sanity Check [ M50B25TU ]

[QUiKSR20]

TLDR - 95 OBD1 M50B25TU Vanos Timing Sanity Check ( not E30 but I know the engine is discussed alot here as well ).

Hello All,

Long story short I purchased a '95 325ic with 150k miles, I noticed every 200 miles or so the coolant light would come on and
the coolant would be low. After looking top to bottom finding nothing external I decided to pressure test the system for leaks
and found the dreaded coolant in cylinder 3 ( Ugh Head Gasket Time ).

Time to do the full coolant system overhaul, all the hoses / parts etc.

While dissembling the head and cross referencing numerous guides / videos online I think my cam timing was 1-2 teeth off
both on my vanos chain and main chain ( maybe this is why the car felt a tad sluggish ). Dont get me wrong the car
idled perfect, revved smooth etc I just expected it to feel snappier than the m20 in my E30 ( maybe this is part of the issue ).

Can any of you guys verify the following :

1. Was my timing off on the main chain
2. Was my timing off on the vanos chain
3. Did I fix them both correctly

I would greatly appreciate it as Id hate to do this wrong, I wanna enjoy the rest of the summer in the vert

This is how I found the Vanos sprocket at full lock -



Vanos Rotation ( before & after videos )

Before ( how I found it )

After ( appears it was off a tooth )

Main Chain ( before & after )

Before ( how I found it )



After ( from what I read has to be to left not center )



Thanks in advance, I truly appreciate anyone taking the time to review.

DG

*ps sorry for the pic sizes but wanted it to be clear.

[KIRIEIW]

It appears you assembled it wrong, referring to the last pic you uploaded. You need to set tension on the MAIN timing chain, and center the exhaust cam sprocket exactly how it was before you took it apart. Leave it alone at that point, your done. You on the other hand turned the sprocket "All the way to the left". I doubt it would affect engine timing how you have it installed but I sure would have assembled it as it was since you NOW have it assembled a "few teeth off". Take it back apart and do things right.

You seem to be getting the term "Cam timing" mixed up with "VANOS timing". Right now your main chain sprocket isn't clocked properly. Fix that first then go onto installing the VANOS sprokets/ chain.

A pretty good video can be found here, you can only type so much but a video explanation is key to a good install;

https://www.youtube.com/watch?v=8ACzOE7nV6g

[mike87]

See below for reference:


FCP:

https://blog.fcpeuro.com/how-to-set-timing-on-a-bmw-e36-m50tu-m52-s50-s52-engine

If you're reusing timing chain:
You will want to line up the holes on the camshaft to the "windows" on the camshaft sprocket so that the holes align to the left. You can move the sprocket on the chain by simply lifting a link and shifting the whole thing over one tooth at a time. There shouldn't be any slack on the timing chain on the right side at this point.
If you're using a new timing chain:
You will want to line up the holes on the camshaft to the "windows" on the camshaft sprocket so that the holes are centered. You can move the sprocket on the chain by simply lifting a link and shifting the whole thing over one tooth at a time. There should be no slack on the timing chain on the right side at this point.
Once the exhaust camshaft sprocket is correctly oriented, install the timing chain dummy tensioner so that tension is applied to the tensioner guide rail. There shouldn't be any slack on the timing chain. The holes on the camshaft and the holes on the camshaft sprocket should be perfectly centered.


DR VANOS:
ME: Hi, hope you are well. I am rebuilding my S50US and I am at the stage where I am installing the camshaft sprocket onto the exhaust camshaft and I need to align the holes to the left sides of the holes in the camshaft sprocket. I have a brand new timing chain, brand new chain guides, brand new camshaft sprocket and a brand new crankshaft sprocket as well. I've read online that because I have all new equipment here, the hole needs to be dead centered before I apply chain tension as there will not be much slack in the chain to begin with. I am unable to get the holes perfectly center when I put the special tool tensioner in, and in fact, it shifts the holes very slightly to the right side of the holes in the camshaft sprocket see attached photo (chain tensioner is in). Would you happen to know what is the correct orientation to put this piece back together? I'm super nervous about this part because I don't want to bend my valves upon startup of a 12-month long build.


DR VANOS RESPONSE: The slots are there to allow the sprocket to move slightly when chain tension is applied (before tightening the torx bolts down), so it's self adjusting. Having it dead center does nothing, and there's no reason to treat brand new parts any differently than the old parts. It's very straight forward and virtually impossible to bend the valves unless the cams are way off. Take a look at our instruction PDF for installing the gears and vanos:
https://cdn.shopify.com/s/files/1/00...les/stage2.pdf

[QUiKSR20]

It appears you assembled it wrong, referring to the last pic you uploaded. You need to set tension on the MAIN timing chain, and center the exhaust cam sprocket exactly how it was before you took it apart. Leave it alone at that point, your done. You on the other hand turned the sprocket "All the way to the left". I doubt it would affect engine timing how you have it installed but sure would affect the VANOS operation, since you NOW have it assembled a "few teeth off". Take it back apart and do things right.

You seem to be getting the term "Cam timing" mixed up with "VANOS timing". Right now your main chain sprocket isn't clocked properly. Fix that first then go onto installing the VANOS sprokets/ chain.

A pretty good video can be found here, you can only type so much but a video explanation is key to a good install;

https://www.youtube.com/watch?v=8ACzOE7nV6g

Are you sure I timed it wrong ? ( maybe were both right in different situations ) I didnt move it all the way to the left, I moved it backwards one-tooth to match the guidelines for reusing your timing chain.

Im aware of the video above ( the commenter right at the top of it "M3NACE" has a ton of DIY videos ) and is the one that vouched for it to the left of the bolt hole..

Video - https://youtu.be/O1gVskqp2Xc?t=291

Also FCP's blog post here [ https://blog.fcpeuro.com/how-to-set-...s50-s52-engine ] States :



Heres the picture of their chain sprocket in the DIY from FCP ( looks to match mine )




From the Bently Manual ( page 108 )



Please confirm if you still think mines wrong ...

Just want to be completely sure im following what you said, I think Hans video is for a new chain.

Thanks for taking the time to respond regardless, Ive done a ton of research before I even made the post... Been playing with these damn BMW's for the great part of 20 years, Just not a ton of Vanos models.

[KIRIEIW]

I personally would have centered it but like I said, doubtful it would affect engine timing. You tighten that sprocket to spec when everything is at TDC and once it's tight that's it. That sprocket isn't going to move anymore. Did you pre-tension the timing chain before tightening that sprocket though? The sprocket moves a bit when you tension the chain. It's usually a tad bit off but once you put tension on the chain they'll center to the slots in the sprocket.

All I can say is you definitely should take it all back apart and rotate that sprocket one or two teeth over if you didn't pre tension the chain.

[KIRIEIW]

Here's a screenshot of the official BMW instructions we have at our dealership showing how to install that specific chain sprocket. They want you to start with the holes slightly off like I was saying earlier and once you tension the chain, it will center on the sprocket. I personally wouldn't take into account the "chain stretching" / stuff your reading online. That's a guessing game.. it's anyone's best guess how much the chain has stretched over 20yr of use. Besides, setting pre-tension on the chain before tightening the sprocket down takes that into account.

[QUiKSR20]

Here's a screenshot of the official BMW instructions we have at our dealership showing how to install that specific chain sprocket. They want you to start with the holes slightly off like I was saying earlier and once you tension the chain, it will center on the sprocket. I personally wouldn't take into account the "chain stretching" / stuff your reading online. That's a guessing game.. it's anyone's best guess how much the chain has stretched over 20yr of use. Besides, setting pre-tension on the chain before tightening the sprocket down takes that into account.

THANK YOU!! Pictures help... Its just confusing at first, From your BMW instructions it sounds like you align it left how I put it, then the tensioner tool pulls it into the middle ( it doesnt move that much ) so if the ultimate goal is middle ill put it back to where I found it.

I personally would have centered it but like I said, doubtful it would affect engine timing. You tighten that sprocket to spec when everything is at TDC and once it's tight that's it. That sprocket isn't going to move anymore.

Makes Sense, Got it.

Did you pre-tension the timing chain before tightening that sprocket though? The sprocket moves a bit when you tension the chain. It's usually a tad bit off but once you put tension on the chain they'll center to the slots in the sprocket.

Im not to that point yet ( my head isnt back from machine shop yet, Just ironing out the steps so theres no suprises when the time comes in a week ).

ILL MOVE IT BACK 1 TOOTH ( Thats the only change I made for the rear main gear )

I was only marking everything for disassembly and when I saw it centered I thought it was wrong, I found it like your last picture in the sequence and thought it was suppose to look like your picture in the first sequence.

Steps from what I gather :

1 - Put cam-gear back 1 tooth ( thats where it was originally and will be centered )
2 - Set dummy tensioner finger tight which will move that gear a tad ( this will stay like this until the full vanos setup is complete and then replace with real tensioner )

AT THIS POINT THE MAIN CHAIN STEPS ARE DONE

3 - Move onto the rest of the vanos install steps which Im pretty sure I understand 100%.

All I can say is you definitely should take it all back apart and rotate that sprocket one or two teeth over if you didn't pre tension the chain.

KIRIEIW,

Thanks for posting that picture which is super clear, I can still re-assemble like your telling me to do it.

When re-assembling ill follow the guidelines you posted above ( really appreciate the incite ), rewatching the videos a second time ( hans garage / m3nace ) its very easy to follow.

Can you confirm atleast my vanos was wrong and is now correct?


Vanos Rotation ( before & after videos )

Before ( how I found it, didnt have full spectrum movement side to side )

After ( now has full movement )

The way I found it wasnt allowing it to have the full spectrum of movement end to end and now it does ( all 4 bolts can be in as well and same rotation works ). Pretty sure I follow how this part works.