FRONT ALUMINUM PLATE

[Slideways]

..

[bigjae46]

..

haha

[PSUEng]

If your torqued the plate to spec, which is necessary for full torsional rigidity, you’d have an issue using them repeatedly.

I'm not being argumentative here, but what kind of issue do you have in mind? I genuinely want to understand the technical basis for BMW saying these must be replaced because, I just cannot understand given what I know. Is it a joint stiffness, is it a fastener wear (I don't think so), is it to look nice like another member posted? I really want to know. Otherwise, I think they are good to reuse--how often, I dunno. This is like the biggest world mystery ever...how many times can you re-use E46 M3 front R/F plate bolts. Hilarious.

[jayjaya29]

Just hypothesizing here. May be for crash protection. If the bolts are stretched more then once they have a lower load rating and may fail during a front-end collision, allowing the engine to submarine.

[bigjae46]

Just hypothesizing here. May be for crash protection. If the bolts are stretched more then once they have a lower load rating and may fail during a front-end collision, allowing the engine to submarine.

I don't think you're stretching a M10? class 10.9 bolt with the OE torque spec.

[jayjaya29]

I don't think you're stretching a M10? class 10.9 bolt with the OE torque spec.

Torque spec for the bolts are 44 ft-lbs + 90° angle (+/- 30°). Nominal torque spec for an M10 10.9 grade bolt is 49 ft-lbs. I think the added 90° angle torque is significantly stretching the bolt more then an additional 5 ft-lbs would.

[bigjae46]

Torque spec for the bolts are 44 ft-lbs + 90° angle (+/- 30°). Nominal torque spec for an M10 10.9 grade bolt is 49 ft-lbs. I think the added 90° angle torque is significantly stretching the bolt more then an additional 5 ft-lbs would.

I thought the torque spec for an M10 bolt is closer to 55 ft/lb to 60ft/lb? Probably close to that spec with a 44ft/lb + 90 deg. Torque spec isn't necessarily stretch to yield. Depends on the standard. Someone would need to measure a bolt to be sure. Wheel fasteners are torqued to spec but aren't replaced each time.

In oil and gas, it has been awhile, I think we used an ASME standard which is not necessarily a torque to yield spec. But we would never re-use fasteners because of corrosion, paint, and the consequences of a fastener failure - massive leak and a large fireball.

Either way, I just caught a couple feet of air going sideways at 60mph and broke a control arm ball joint. The bolts didn't break or shear although I am replacing those bolts because of the impact. So I'm inclined to stick with my blast them on with an impact method.

In the end, we are arguing about a relatively minor detail in a procedure. How many E46 M3s were produced? Now how many times has the front thrust plate been removed? Now how many times have the bolts been replaced? Now how many people have had their front plates fall off or even found a broken bolt? I'm sure there would be plenty of stupid questions about it on facebook complaining about cheap BMW bolts if it was happening.

[Obioban]

I thought the torque spec for an M10 bolt is closer to 55 ft/lb to 60ft/lb? Probably close to that spec with a 44ft/lb + 90 deg. Torque spec isn't necessarily stretch to yield. Depends on the standard. Someone would need to measure a bolt to be sure. Wheel fasteners are torqued to spec but aren't replaced each time.

In oil and gas, it has been awhile, I think we used an ASME standard which is not necessarily a torque to yield spec. But we would never re-use fasteners because of corrosion, paint, and the consequences of a fastener failure - massive leak and a large fireball.

Either way, I just caught a couple feet of air going sideways at 60mph and broke a control arm ball joint. The bolts didn't break or shear although I am replacing those bolts because of the impact. So I'm inclined to stick with my blast them on with an impact method.

In the end, we are arguing about a relatively minor detail in a procedure. How many E46 M3s were produced? Now how many times has the front thrust plate been removed? Now how many times have the bolts been replaced? Now how many people have had their front plates fall off or even found a broken bolt? I'm sure there would be plenty of stupid questions about it on facebook complaining about cheap BMW bolts if it was happening.

If you're gunning them on, you're likely not weakening them. If you're torquing them to spec, you're almost certainly in the plastic deformation range of the bolt.

44 + 90 deg is 100-120 ft lbs.

AFAIK, BMW only specs steel bolts be replaced for torque to yield locations.

[JakeM346]

If you're gunning them on, you're likely not weakening them. If you're torquing them to spec, you're almost certainly in the plastic deformation range of the bolt.

44 + 90 deg is 100-120 ft lbs.

AFAIK, BMW only specs steel bolts be replaced for torque to yield locations.

I think we can forget this here. Some peopLe are obviously resistant to the very basics of engineering. So why waste time…..
let’s let them do like they want too

[bigjae46]

If you're gunning them on, you're likely not weakening them. If you're torquing them to spec, you're almost certainly in the plastic deformation range of the bolt.

44 + 90 deg is 100-120 ft lbs.

AFAIK, BMW only specs steel bolts be replaced for torque to yield locations.

120 ft/lbs? That doesn't rip the threads out of the aluminum FCAB housings? I might have to use the BMFI - that's the big mutha fukin impact

[Bry5on]

Fortunately this is pretty easy to calculate. Since I’m on a phone, let’s make some assumptions and approximate to see if simple math and assumptions tells us the answer.


Assume:
1) 50% stretch is in the bolt and 50% compression is in the joint
2) Effective length (L) is 30mm
3) Thread pitch 1.25mm and 90 degree turn = .3125mm = dl
4) Elastic modulus of steel = E = 200000 N/mm^2
5) Cross sectional area of an M10 bolt = A = 64.5mm^2
6) Tension in fastener is linearly proportional to torque

Case 1: Assume contact but no preload from initial torque
Case 2: Assume linear force proportional to proof torque, add case 1 for total

Case 1 (seat the fastener, turn 90 degrees):
dl = FL/EA
F = E * A * (dl/2) / L (dl is halved because of assumption 1)
F = 200000 * 64.5 * .3125 / 30
F  =  67,188 N

Case 2 (torque to 44, turn 90 degrees):
Proof load (pure elastic) of an M10 10.9 fastener is ~ 53500 N @ 82 ft-lb
Tension at 44 ft-lb therefore ~ 29000 N (due to assumption 6)
Add Case 1 and tension (if we were still elastic, which we’re not) is above 95,000 N.

If our elastic region ends at a tensile load of 53,500 N, then anything above that is causing plastic deformation and permanent stretch. Ultimate tensile load of an M10 fastener is minimum specced to 67,100 N, so the rough math very much agrees that this fastener is going to be yielding, even if you barely torqued it before the 90 degree turn. If you torque it to yield over and over, IT WILL FAIL.

Why is it torqued to yield? I don’t know but I’d guess for frontal impact more than torsional rigidity. If you want to skip torquing to yield, I’d go to 70-80 ft-lb instead, that’s better than failing the bolts from repeated yielding. I replace them and torque to yield, so I recommend torquing to yield. Because I want my car to absorb energy if I smash into something. Because I like safety.

[01SG]

Maths hurt brain.

I think the safety argument would be a more compelling one. However, does anyone have legitimate information on how important the plate is to the safety of the car? Remember, the e36 m3, including the Euro version that is about as heavy as the e46, had no such plate. Of course, it's a much less safe car as well, but I do wonder what role this would really play in a crash scenario.

[Obioban]

I’m pretty sure I remember that plate, at least in promotional materials (whatever they’re worth), being advertised as one of the sources of increased chassis stiffness over the non M.

[Bry5on]

Maths hurt brain.

I think the safety argument would be a more compelling one. However, does anyone have legitimate information on how important the plate is to the safety of the car? Remember, the e36 m3, including the Euro version that is about as heavy as the e46, had no such plate. Of course, it's a much less safe car as well, but I do wonder what role this would really play in a crash scenario.

If it does, I'd bet it helps particularly in a front corner impact where the front longitudinal frame rail is trying to bend inward. This is one of the trickiest crashes to design around. Buckling the aluminum plate in shear takes extra energy (same reason if helps with chassis stiffness). The non-m also has this plate, but it is not braced as well to the control arms and frame rails behind the firewall. We do have an automotive safety engineer here on the forum that might be able to make more educated responses than I can. At one point in my life, I did work at an automotive OEM and was arms length involved in some of the energy absorption simulation testing as I worked mostly on body structure, I'm no expert though.

[01SG]

If it does, I'd bet it helps particularly in a front corner impact where the front longitudinal frame rail is trying to bend inward. This is one of the trickiest crashes to design around. Buckling the aluminum plate in shear takes extra energy (same reason if helps with chassis stiffness). The non-m also has this plate, but it is not braced as well to the control arms and frame rails behind the firewall. We do have an automotive safety engineer here on the forum that might be able to make more educated responses than I can. At one point in my life, I did work at an automotive OEM and was arms length involved in some of the energy absorption simulation testing as I worked mostly on body structure, I'm no expert though.

Sounds like you'd have a better understanding than most. Interesting.