Does anyone know why it is important to install the top timing chain guide before torquing anything down during a timing chain exchange?

 

I'm also wondering if it's necessary to pretension the timing chain when using the newer style tensioner or if you can just go ahead and torque it down and then do the Vanos sprockets?

 

To your first question, I don't think it is. If you've done everything else right, it shouldn't matter. You have another thread on here where the forum helped with assembly order of timing chain. Follow that and you should be fine. Personally I forgot the top guide until everything was torqued, put it on after, and has been fine as far as that is concerned. If someone took their valve cover off for fun and noticed the top guide was broken, I would just replace it, I wouldn't redo the whole timing set.
Here's another thread discussing this: R56 Top timing chain guide replacement - North American Motoring

Why not use the special pretension tool? It works as a mechanical hard stop to keep the chain slack in the correct position while you tighten the VANOS sprockets. If you use a part as a tensioner, that side of the chain could pull tight, depress the spring-plunger, and now the chain slack can rotate around with the intake VANOS when torqued and throw things off. Now, I'm not sure this would happen. it might be fine to do what you ask, but I didn't, and wouldn't.

 

I'm not opposed to using the pre tensioner tool, I've just heard a lot of people and even saw one video where it fixed a fault code to not use it and just tension the newer style tensioner to 80nm. I did everything in the recommended order but still have a limp mode and engine light, for implausible exhaust camshaft. I heard on a few other videos and mechanics that the top guide rail has to be put on before tensioning anything. I was wondering why and what difference that would make. I guess it has something to do with the correct travel in the chain. Makes me wonder if that can contribute to the code. I'm going to try and retime the engine to see if I can get rid of the code, but just want to be sure I'm doing everything right this time. The reason I'm worry about using the pre-tensioner tool is because they want you to torque it to a very low spec that I have no tool for and I don't want to rely on guessing. Would you happen to know how many millimeters the threaded side of the special tool that is to be screwed in would be one. It is in correct position? I appreciate your feedback.

 

In the video you mention where a code was solved using the part as a tensioner, was it the same implausible exhaust camshaft code?
Unfortunate, sorry to hear that. This was a timing assembly video that made me feel better to watch when I did mine. Ironically, he did it your way using a part as a tensioner. The one thing I really like in the video is that he used a tool to hold the camshafts centered in the holding tool, while he tensioned the VANOS sprocket...so that the cams didn't tend to roll a bit with the bolt tension. I mean a wrench, I don't think when he shoved feeler gauges between the cam and the tool, that that likely did much.

I don't think that top guide could actually hurt or help timing. It's too flimsy to really pull a chain one way or the other.

I didn't have a wrench that came close to 0.6nm either, for the pretensioner tool. What i did was turn the tool in until I could tell nothing was springy, that it pretty much had the chain pulled tight (by fingertips), gave it a tiny snug with a wrench, and it came out fine. I don't understand your last question sorry. I'm thinking you're asking about the thread of the pretension tool. If that's the case, are you using a purchased camshaft timing kit? They usually come with the pretension tool.

 

It was not the same code, he had 2da0 and I have 2da1. It's the closest code I can find to the one I have. I cannot for the life of me find anyone or anything that references that code. It must be serious if it goes into limp mode though. I watched the video, interesting that he didn't use a pre-tensioner unless I missed that part somehow. Overall, good video. I have probably seen 20ish videos on mini timing chains now. I have the kit that comes with the pre-tensioner, what I was asking is kinda hard to understand now that I read it back, but let me try to rephrase it. After you tighten the pre-tensioner to where it should be, how much of the threaded center piece should be twisted in by millimeters? I'll try to send a picture. The part that's circled. How many millimeters should that threaded section be when it's in place.