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Discussion Starter · #1 · (Edited)
After removing the front subframe and steering rack for rod bearing replacement, I decided I didn't want to struggle with the engine mount bolts or the banjo bolts on the power steering rack. I'm not sure about everyone else, but it took me HOURS to remove the bolts from the subframe to the engine mounts and getting at the banjo bolts with the subframe in the way was equally painful. There was just no good angle from above or below to get a wrench on any of these and I'm also not a fan of dumping power steering fluid down the rack and all over the subframe (and, ultimately, on the floor).

So, I decided to modify the rack, new engine mounts, and the subframe so that the subframe can be removed independent of the rack and the bolts to the rack and engine mounts can be removed from below.

I purchased EZ-LOK threaded inserts in order to thread into the engine mounts and into the steering rack.

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You can purchase these on Amazon or McMaster Carr. I purchased the inserts with English external threads, particularly because the M10 thread inserts that use an M16 external thread require a tap drill that's far larger than the 9/16"-12 thread (like around 0.100") and I didn't want to drill a larger hole than necessary through the steering rack mounting holes.

So, at this point, I'll throw out the disclaimer. I would recommend using a drill press. If you don't have one, don't attempt this if you don't have a lot of experience and can't drill clean and straight with a hand drill.

Clamp each of your engine mounts to a bench or in a vice and drill through the mounting holes with 27/64" drill bit. Use cutting fluid or you'll gunk up your drill bit with aluminum or break it if you're drilling by hand. Again, it's very important that you drill these straight and not off at some angle that isn't normal to axis of the bolt. If they're not straight, your bolts will not thread into the inserts.

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After drilling, clean up the hole and debur. Then, tap with 1/2"-13 tap. DO NOT use a cheap tap. The last thing you want to do is break off a cheap tap in your new engine mount. I recommend a spiral tap. Use cutting fluid to tap. If you're not using a spiral tap, break the chip you're cutting by backing up a quarter turn when it starts to feel difficult to turn the tap in the cutting direction.

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Also, do not tap all the way through. Push the tap a few threads longer than the length of the insert or no further than the bottom of the tap flush with the bottom of the hole. You want to drive the insert in so that it stops and it can't thread in any further. In the rare case that the Loctite breaks free on the insert, this ensures that you'll always be able to get the bolt out.

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I will install the bolts with a dot of blue Loctite when I reassemble the vehicle since it will be steel on steel thread engagement rather than steel in aluminum thread.

Now the steering rack:

Find a way to fix the rack to a bench or on the table of your drill press like shown.

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I started on the front side of the rack. Use a 31/64" drill bit and make sure you drill straight. These holes are even more important than the engine mounts because you're dealing with a more expensive part. Don't forget to use cutting fluid.

I would highly recommend using a good quality 9/16"-12 spiral tap on the rack if you weren't already planning to. You don't want to have to get a broken tap out of your rack.

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Now the back side of the rack:

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Use blue Loctite on the bolts when reassembling since the eccentric locknuts are eliminated here.

On the subframe, you'll need to drill out the threads for the engine mounts for an M8 clearance. Use an 11/32" or 8.8 mm drill bit.

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On the bottom side of the threaded bosses of the subframe, I also chose to trim a 1/4" (6 mm) from them to reuse the original hardware. If you install the inserts to the very bottom of the engine mounts, you might be able to get away without doing this, but it would be cutting it close. Otherwise, you can buy longer bolts to use. If you get longer hardware, use torx head or SHCS. A standard cap screw with a hex head wouldn't leave enough room to get a socket over them.

This should hopefully turn subframe removal into a much easier affair.
 

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Interesting. I recently installed rod bearings in my E60. While I found the banjo bolt removal and installation to be a pain, I didn't struggle much with the engine mounts. This modification would certainly make things easier, but I don't plan on dropping my subframe too often. Hopefully I'm not eating my words soon. :)

Are you worried at all about whether the new engine mount setup will be able to secure the motor at full torque? Is there a risk of one of the mounts pulling out?
 

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Discussion Starter · #3 · (Edited)
Are you worried at all about whether the new engine mount setup will be able to secure the motor at full torque? Is there a risk of one of the mounts pulling out?
Not at all. The original setup has the bolts threaded into the aluminum bosses on the subframe. In my setup, the aluminum engine mounts are threaded with a larger, stronger thread than the M8 in the subframe and then inserted with steel threads. The only real risk I can see is screwing up the the whole process and then having to go even more out of the way to fix it or have someone else fix it.
 

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Discussion Starter · #4 · (Edited)
I plan on keeping this car forever, so I assume I'll be back under there again for one reason or another, if not to replace rod bearings again.

I'm also the kind of person who can't stand not having things the way I want them if I think they could be better, I would rather spend a few hours on a modification that brings satisfaction than a few hours reinstalling four bolts and two banjo bolts while cursing BMW into oblivion ?.
 

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Discussion Starter · #5 ·
I think I should also mention that you can buy these threaded inserts at twice the length the ones I bought, if you'd like to have a longer thread engagement. The longer inserts are actually just the right size for both the engine mounts and the rack. I think it would be overkill, but if you have any feeling of insecurity about whether the threads can take the torque of the engine, you wouldn't with those. I'm not sure if you can get the longer ones on Amazon because I didn't check, but I know they're on McMaster for a reasonable price.
 

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Do you have stock headers? If so then removing the single nut from the top is straightforward. May need extra extensions but that's it. Mounts come out with subframe this way.

As for the rack, yes the lines are a PITA. That's why you disconnect both lines at the pump and cooler ends. Both lines come out with the rack and subframe as well.
 

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Discussion Starter · #7 ·
Yes, I have stock headers. Removing the mounts from the engine brackets wasn't a big deal, though. I just want the ability to unbolt from subframe without having to wrench on them one tooth at a time. Not sure how some people claim to get them from above... I tried with two universal joints and still couldn't get them from above.
 

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Yeah I've heard people struggle with the top nut as well. The one case in here was due to aftermarket headers. When I did mine I had no issues, no idea why some have trouble with it?

Props to you for creative thinking tho!
 

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@NAK91
Nice solution. I didn't have much trouble at all accessing the nut (15mm deep socket I think ) from the top with a long extension, I thought I would need a swivel but not at all. I just put mine back together last week. I have left it out for awhile as I was on other parts. I think the engine mount mod will be fine with how you have it as it does actually just bolt through to a tapped hole in the subframe and the torque there is only 21 nm.

I think your steering rack mod may need some extra care. I'm not saying this to rain on your parade, but the is a potential safety concern here, specifically the rack attachment to the frame is under very high loads when high speed cornering. I think the M5 can generate about 0.98g lateral acceleration, that force is applied to the rack then to the frame, which turns the car.

The fasteners are very high strength because of the very high clamping load. If those joints fail, you will not be able to steer the car since the rack will then "float". I came to realize this myself 3 weeks ago when I went to remount the rack to the subframe. The torque sheet in ISTA+ is a bit confusing, I've attached it here.

The bolts and nuts should be replaced according to BMW. They are class 10.9 tensile strength M10 bolt, with a 56 nm, 90 deg torque angle. I'll have to double check on my torque log, but I believe this ended up being about 90 nm. While not specifically called out as such I believe these 4 bolts are TTY, which is why it says "Replace screws and nuts".

The mistake I made: The confusing part is when you look at the sheet, one could read the row below the blue box I highlighted that "E60/ Four Wheel Drive" is the one you need, which calls for 120 nm on a M12 fastener. I was just trying to get it back together quickly as it is there is no heat where I am working. I set my wrench for 120 nm, without really questioning the sheet. When I got to 100 nm, I was like WTF, this is really tight. At 105 nm I was like f*ck this bolt is stretching I can feel it so I stopped and re looked up the spec. I realized that the proper row is the one that I have boxed which is what I referenced in the prior para. Makes sense too since 120 nm is way too high for a M10 bolt even a 10.9 class. I had to order new bolts and nuts, and those bolts are not cheap.

In short, I'm saying that unless you have calculated the loads, amount of thread engagement, and specified the right thread tolerance, a class 10.9 bolt threaded in aluminum will not be able to exert the same amount of clamping force as a class 10.9 bolt and nut that sandwiches the aluminum flange. Again I'm only saying this for your own safety. Maybe what you have done is in fact totally fine. Just putting it out there to consider.
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I decided I didn't want to struggle with ... the banjo bolts on the power steering rack
It is possible to pass the steering rack through the sub frame without disconnecting the steering rack. Lower both; then separate the rack and IIRC you take the drivers out first by moving the subframe in that direction, then tilt to remove the passenger side. I then rotate the rack to be along the drivers door sill.
 

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Discussion Starter · #11 ·
@gmtegear Totally agree with you. It is my intention to calculate thread strength before reinstalling the rack... particularly because I didn't order the inserts I had intended to order which would have had thread engagement of around 0.800". If a 9/16"-12 at the current thread engagement ends up looking a little weak in terms of FoS, I'll end up replacing the inserts with the longer ones I had originally intended. I'll keep everyone updated on what I do.
 

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Discussion Starter · #12 ·
Everything checks out ok. I've calculated that it would take somewhere around 240-300 lb ft to generate enough force to begin approaching the shear strength of aluminum across the area of the 9/16"-12 threads at their engagement... About 330-400 nm. This was calculated loosely, but on the side of caution in a couple different respects, which would make my estimate relatively conservative. So, it sounds like the bolts would begin to yield in tension before it would strip out the threads (I'm only assuming this since @gmtegear 's experience torquing to over 100 nm began to stretch his M10 hardware). That calculation also doesn't include any effect that the loctite has on the strength of the joint, if any at all.

If you do this, however, I would still recommend using an insert that spans the whole length of the flange because it doesn't cost you any more.
 

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Very well done. Also I was retorquing the original M10s (which I didn't know were TTY since I was reading the incorrect line). I'm sure that the process of trying to retorque TTY bolts to 120 nm was well on the way to having the bolt fail as it started to get easier to torque.
 

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Discussion Starter · #14 ·
Quick update.. I found a handful of 5/8" injection mold core pins in a box with some of my tools, so I've decided to use those to make inserts. While I'm perfectly confident the EZ LOK thread inserts will easily handle the torque required at a thread engagement that is the width of the steering rack flange, using these core pins would just be super cool since they're made out of tough tool steel and would hold up very nicely over repeated removal of the rack compared to the lower quality steel of the EZ LOK inserts and I'd never have to worry about bunging up the threads... not that I plan on removing the rack or the subframe on a regular basis ?.

I'm a little bored, though, and I've got some time on my hands while I wait for a few parts so I couldn't pass up the opportunity to take advantage of my find. The core pins are perfect for this, too... they're 0.0005" oversized and have a 1/4" thick head as well. I also happen to have a 5/8" reamer, so I can bore the mounting holes out and press them in after I drill and tap them for M10 x 1.5.

Also, if you've got a small lathe or know someone with a small lathe, I would recommend this route as well simply because it's not much more work and you can't beat the price of a core pin for the ground OD and the quality of steel it is. You can easily get these for $5-10 each from PCS, Progressive, or DME (or any other mold component supplier). A bag of the EZ LOK inserts is gonna cost a little over $20 and the core pins will maybe cost you $30-35. Just make sure not to buy hardened core pins. You want them around 30-35 RC and no higher than 40. If you buy hardened core pins, you'll never be able to drill and tap them and they'll also lose some of their toughness.

I'll update again when I get started on this.
 

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Discussion Starter · #15 · (Edited)
Ok. Got the core pins cut to length, drilled and tapped, and press fit into the rack. It was relatively easy to do since the core pins are all about 0.0005"-0.001" oversized, I just drilled the rack out and reamed it with a 5/8" reamer and it left me with a perfect press fit. The core pins are made out of some pretty tough steel, so had to be careful tapping. They weren't hardened, though, so perfectly doable. It wasn't really necessary, but I also put some bearing retaining compound (loctite 601) on the inserts before pressing them in.

I recommend this route now, if you've got the resources to drill, tap, cut to length, etc., just because of the quality of the steel.. You'll never have any problems with these wearing out and you'll certainly never worry about them failing under load because they're massive overkill ?.

Core pins from PCS ~30-35 RC
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All pressed into the rack:
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Discussion Starter · #17 ·
Test fit is perfect.. Should be a quick off and on from now on. I'll be back in the crankcase again at some point for vanos related maintenance when that comes up. I'll let everyone know if leaving the rack attached at the banjo fittings is feasible. It would be nice to just zip tie the rack up somewhere without having to break those lines loose and drain the fluid all over the place.

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Im sure you know this but to my surprise the blue bolts for engine mounts are single-time use only and require new ones each time because they are aluminum
 

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Discussion Starter · #20 ·
The engine mount bolts as well as the bolts for the steering rack are steel. I'm not sure about the engine mount bolts, but the rack mounting bolts are TTY.
 
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