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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N20, N26, B46, B48 Turbo Engine / Drivetrain / Exhaust Modifications > Clearing Up Timing Chain Inconsistencies
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      11-27-2017, 07:43 PM   #45
mattwong92
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Quote:
Originally Posted by madmortar View Post

Lol dealership is refusing to do work. Saying "they cannot reproduce the issue"
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      11-28-2017, 03:56 PM   #46
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Too little too late - I hate being right.

Quote:
Originally Posted by motorwerkeman
Willing to put money that this will not happen to engines made after 04/2015. Timing chain was replaced with a new part # 01/2015 and oil chain was replaced with new part # 04/2015 - meaning it took 4 years for BMW to track down and solve the problem. Both chains stretch and a service bulletin should have been issued.

I have not heard of a single case on a newer car (04/2015 or newer) with this happening and believe the new chains fix the issue until I am proven wrong.
The ELW supports this 100%.

I needed an complete engine replacement as a result of chain failure and was somewhat covered, but still paid many thousands out of pocket on a vehicle 3 months out of warranty. So while this may look like BMWNA 'doing the right thing' it has taken them far too long to recognize the issue when they could have issued this ELW over 2 years ago based on what we know.
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      11-30-2017, 05:39 PM   #47
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So update:

Got my car back from the dealership, did not get any work done. They brought in a Engineer Rep from Germany who happened to be visiting the dealership to look at my car (even got him on dash cam lol).

He explained that:
- when the n20 engine cams lobes come to rest vertically straight up at a very specific point the lobe will rotate back slightly (very rarely will it do so it needs to come to a stop exactly at that point).
- When the lobe rotates back slightly on engine stop, there will have slack on the chain that you see in my video (enough to lift the chain 1-2 cm off the guide)
- He said he was very surprised i even noticed this in my car as no one ever looks at it and happens in a very rare use case.
- Otherwise you will see very slight play in the chain, and movement side to side up and down depending on oil pressure due to the hydraulic tensioner used when the lobe takes up all the rest of the slack on the chain.
- Overall listening to my engine he said it sounded very healthy, and the only cases in which the timing chain shows symptoms of going out is the VERY loud high pitched whining noise. Additionally as more and more slack appears in the chain over time you will hear loud noises that sound like rod knock.
- Overall he said a lot of customers are concerned with their timing chains but from every single n20 that has been completely broken down in the shop for the repair they have VERY noticeable sounds and has affected a very low number of cars.
- From the engines and cars that have had this issue they were being driven or had been going over the expected oil change intervals at around 15-20k miles before changing.

Not sure if this info is helpful or not but posting here anyways thanks!

Last edited by mattwong92; 11-30-2017 at 05:45 PM.
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      11-30-2017, 06:07 PM   #48
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Thanks for your input.

Just confirms what i heard from multiple sources that i asked about the problems with timing chains on BMWs and other problems. Someone correct me if im wrong but I still think that looking up forums for problems on specific car can be misleading in a way that the problems are almost always the main discussion meanwhile the cars that work with no problem are nowhere to be heard from.

I think a lot of people are still concerned with what BMW and other carmakers are doing in terms of service intervals and other stuff. I have always been saying that the technology in our cars get tested in a way that we cant even imagine. (just look at G20 cars already beeing tested and still 2 years before its even showed to the public) Im saying this because a lot of people are concerned about Auto start/stop and other things which IMO shouldnt really matter in timeframe that we use our cars.

The mistakes i see people do with cars is mostly trashing completly cold car or ignoring service intervals. It has been said a lot of times that we should stick to the original service intervals that are set in our cars BUT changing oil + filter at half that should basically remove any concern that we are not treating our machines the right way. ( The same people then sit in a warm car in a car park because the engine needs to cooldown before you can turn it off )

Maybe i dont have nearly enough experience to talk about this but i still think that 95% major problems that occur on a car can be noticed before the catastrophy if you once in a while listen to your car and not ignore small problems that show up.
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      11-30-2017, 06:07 PM   #49
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Quote:
Originally Posted by mattwong92 View Post
So update:

Got my car back from the dealership, did not get any work done. They brought in a Engineer Rep from Germany who happened to be visiting the dealership to look at my car (even got him on dash cam lol).

He explained that:
- when the n20 engine cams lobes come to rest vertically straight up at a very specific point the lobe will rotate back slightly (very rarely will it do so it needs to come to a stop exactly at that point).
- When the lobe rotates back slightly on engine stop, there will have slack on the chain that you see in my video (enough to lift the chain 1-2 cm off the guide)
- He said he was very surprised i even noticed this in my car as no one ever looks at it and happens in a very rare use case.
- Otherwise you will see very slight play in the chain, and movement side to side up and down depending on oil pressure due to the hydraulic tensioner used when the lobe takes up all the rest of the slack on the chain.
- Overall listening to my engine he said it sounded very healthy, and the only cases in which the timing chain shows symptoms of going out is the VERY loud high pitched whining noise. Additionally as more and more slack appears in the chain over time you will hear loud noises that sound like rod knock.
- Overall he said a lot of customers are concerned with their timing chains but from every single n20 that has been completely broken down in the shop for the repair they have VERY noticeable sounds and has affected a very low number of cars.
- From the engines and cars that have had this issue they were being driven or had been going over the expected oil change intervals at around 15-20k miles before changing.

Not sure if this info is helpful or not but posting here anyways thanks!
Would this affects n26 also?
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      11-30-2017, 07:20 PM   #50
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Originally Posted by jan31 View Post
Would this affects n26 also?
He said it affected all 4 cylinder designs.
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      11-30-2017, 07:26 PM   #51
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Quote:
Originally Posted by pustinek View Post
Thanks for your input.

Just confirms what i heard from multiple sources that i asked about the problems with timing chains on BMWs and other problems. Someone correct me if im wrong but I still think that looking up forums for problems on specific car can be misleading in a way that the problems are almost always the main discussion meanwhile the cars that work with no problem are nowhere to be heard from.

I think a lot of people are still concerned with what BMW and other carmakers are doing in terms of service intervals and other stuff. I have always been saying that the technology in our cars get tested in a way that we cant even imagine. (just look at G20 cars already beeing tested and still 2 years before its even showed to the public) Im saying this because a lot of people are concerned about Auto start/stop and other things which IMO shouldnt really matter in timeframe that we use our cars.

The mistakes i see people do with cars is mostly trashing completly cold car or ignoring service intervals. It has been said a lot of times that we should stick to the original service intervals that are set in our cars BUT changing oil + filter at half that should basically remove any concern that we are not treating our machines the right way. ( The same people then sit in a warm car in a car park because the engine needs to cooldown before you can turn it off )

Maybe i dont have nearly enough experience to talk about this but i still think that 95% major problems that occur on a car can be noticed before the catastrophy if you once in a while listen to your car and not ignore small problems that show up.
Since I have had my turbo replaced (I am second owner first owner blew it out from not properly letting it cool down after running each time) under warranty after each drive regardless of engine temp, I always allow proper cool down with under 2k rpm pulls around 1-5 miles out from my home, and let the oil circulate within the turbo before turning off the car. Additionally I allow proper warm up before any spirited driving (I literally drive like a grandma until it warms up in eco-pro).

Outside of this I do all my own oil changes with filter changes every 5k miles with changes in oil weight depending on winter/ summer driving months. At 5k miles the oil is noticeably dark however still has golden tint (nothing like my E30 :P but then again I love the simplicity of my E30)

Before and after each drive again earlier I mentioned this I check the under the oil fill cap (which is how I noticed the slack on the chain prompting me to bring the car in for the explanation).

I also turn off all air vents/ sound system for drives to listen to the clackity clack on cold start of those high pressure fuel injectors to make sure no sounds are outside the ordinary.

Hopefully my craziness makes this engine last

Whats funny is while my car was in the dealer bay, the dash cam recorded the techs driving the car in where they were talking about a 528i with the n20 engine which had had its chain explode. They were talking about how the guide had shattered due to the slack, and there were visible metal chunks within the oil.

Last edited by mattwong92; 11-30-2017 at 07:32 PM.
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      11-30-2017, 09:13 PM   #52
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Quote:
Originally Posted by mattwong92 View Post

Whats funny is while my car was in the dealer bay, the dash cam recorded the techs driving the car in where they were talking about a 528i with the n20 engine which had had its chain explode. They were talking about how the guide had shattered due to the slack, and there were visible metal chunks within the oil.
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      12-01-2017, 04:40 PM   #53
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Just curious though if theres any engineers in this forum if the use case makes sense?

So basically the explanation broken down all over again is:
1. The n20 engine and its 4 cylinder brothers and sister variants when the overhead cam lobe comes to rest exactly vertical to the valve it will rotate back slightly causing the chain to exhibit quite a bit of slack as my video documents here:


Again this is a VERY rare instance as the lobe needs to be exactly in position to rotate backwards slightly when the engine is turned off. This will exhibit the slack in the chain regardless of the temp and oil pressure.

2. Overall the n20 engine and its variants will have wiggle in the chain (not as much as my video shows) when cold because the engine uses a hydraulically actuated tensioner which gets tighter when the oil pressure in the engine builds. So therefore when the engine is cold you should see wiggle, and when its hot and normal operating temps you should see something like this:


Overall BMW has noted the issue and is why they issued the ELW. However they also noted that the low amount of cars actually exhibiting this issue all had the following in common:

A) Prolonged periods of no oil changes 15-20k miles
B) Loud whining noises outside of the normal cold start whining
> engineer said that the n20 engine is normally quite loud as the pistons are oversized and actually expand as the engine warms up so on cold starts they actually bounce side to side slightly within the piston bore within the engine block
C) When the timing chain has eventually stretched it will exhibit loud almost rod knock like noises from the front of the engine

It seems like what happens to me is:
1. prolonged period of no oil changes causes the chain to heat up and stretch prematurely
2. the stretch causes vibrations within the chain dragging along the guide causing it to shatter or break

I just wanted to see if this is actually a logical explanation? Being a Quality Assurance Engineer wouldn't the following also make sense?

- when the lobe happens to rest vertically and exhibits slack, on cold starts when the tensioner is NOT actuated fulled by oil pressure the slack causes the chain to drag on the guide vibrating it over spec?
- When using start stop (starting and stopping the engine quite a bit) increases the probability that the lobe will come to a rest vertically and rotate backwards while the engine is off, and when the user has not warmed up the engine the same thing happens with the chain?
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      12-01-2017, 05:05 PM   #54
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The lobe being vertical isn't that rare, as there's four pairs of them per camshaft, making for eight positions per rotation of the camshafts where there are vertical lobes, not one. Pictures of the old chain design versus new show that the new is less likely to stretch, so obviously that was what they determined to be the effect, though I'm not so sure they really know what causes some chains to stretch, just that they do.

The design of the tensioner has changed too, so that's part of the problem. It seems what happens is that when the chain stretches enough and the tensioner is no longer able to provide enough tension the chain can wobble enough to damage the guide, which allows more wobble, which damages the guide even more, and the snowballing effect eventually causes the chain to break.

If the damage occurs when the engine is cold then start-stop doesn't explain it, because the ASS doesn't work with a cold engine.
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      12-07-2017, 02:01 PM   #55
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https://www.carcomplaints.com/news/2...g-chains.shtml
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      12-07-2017, 09:17 PM   #56
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Quote:
Originally Posted by pustinek View Post
Thanks for your input.

Just confirms what i heard from multiple sources that i asked about the problems with timing chains on BMWs and other problems. Someone correct me if im wrong but I still think that looking up forums for problems on specific car can be misleading in a way that the problems are almost always the main discussion meanwhile the cars that work with no problem are nowhere to be heard from.

I think a lot of people are still concerned with what BMW and other carmakers are doing in terms of service intervals and other stuff. I have always been saying that the technology in our cars get tested in a way that we cant even imagine. (just look at G20 cars already beeing tested and still 2 years before its even showed to the public) Im saying this because a lot of people are concerned about Auto start/stop and other things which IMO shouldnt really matter in timeframe that we use our cars.

The mistakes i see people do with cars is mostly trashing completly cold car or ignoring service intervals. It has been said a lot of times that we should stick to the original service intervals that are set in our cars BUT changing oil + filter at half that should basically remove any concern that we are not treating our machines the right way. ( The same people then sit in a warm car in a car park because the engine needs to cooldown before you can turn it off )

Maybe i dont have nearly enough experience to talk about this but i still think that 95% major problems that occur on a car can be noticed before the catastrophy if you once in a while listen to your car and not ignore small problems that show up.

Your point here - “Someone correct me if im wrong but I still think that looking up forums for problems on specific car can be misleading in a way that the problems are almost always the main discussion meanwhile the cars that work with no problem are nowhere to be heard from.” is called selection bias. In this case it gives the impression the problem is more prevalent than it is. Data rules the day...until we see the defect rates and data no one will know the extent of the issue. If you are gauging the probability of this happening to your car, based on reading threads like this, you will probably be overly concerned.
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      12-07-2017, 10:13 PM   #57
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Quote:
Originally Posted by scostu View Post
Wow. Thanks for sharing.

Im at 38k and terribly afraid Ill have an issue at some point. I drive a lot for work and racking up miles quick. Oil change every 5k for me. Other than that, fingers crossed...
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      12-07-2017, 11:44 PM   #58
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Quote:
Originally Posted by jthoms1 View Post
If you are gauging the probability of this happening to your car, based on reading threads like this, you will probably be overly concerned.
+1. People go to forums mainly to either get advice or to bitch about a problem. If you're not looking for advice and don't have anything to bitch about chances are you're not going to forums.
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      12-21-2017, 11:45 AM   #59
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If it was just failures due to lack of oil proper oil change intervals BMW could easily deny a problem exists. Furthermore BMW provides service during the first 50,000 miles under warranty. BMW created the CBS algorithms for oil changes. This means a low number of vehicles with lack of maintenance for significant mileage.

If you think your timing chain is going to be fine changing your oil earlier your kidding yourself You may delay it at best. I maintained my Mazdaspeed6 better than recommended and the timing chain stretched. Mazda also did a half way warranty extension to 7yrs/70,000 miles. Mine was well over the mileage and I had to pay for the replacement. If the chain is defective it's going to fail
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      12-21-2017, 12:24 PM   #60
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From experience with a different platform... cam correlation codes were the first symptom to appear before and outright failure...

Not positive that would apply here but would make sense if it did.
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