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?