Reinforcement plates vs structural foam ?

[kermmmit7]

What's better ? I seen that most people use plates but probably most of them had already cracks .

[eacmen]

Most people these days are getting on the vincebar topside reinforcement train.

I've used the Redish plates with Mason XBrace and seen no issues.

The foam is generally considered to be a band aid from bmw to get cars running through the warranty period.


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[AussieE46M3]

Avoid the foam entirely. It's not a reinforcement nor will it prevent failure from occurring.

Get yourself a good set of weld in underside reinforcement plates and a chassis rail to RACP plates to eliminate the possibility of the boot floor pulling away from the frame rails and you should be good to go.

On a side note, it's a great time to change out the old subframe & diff bushes during a reinforcement. Solid subframe and stock diff is the ideal combo. Have been daily driving my M3 this way for years.

[Syfon]

Foam doesn't fix the issue. Neither does plates.

Plates + topside & frontside reinforcement (i.e. Vincebar or CMP kit) is the only permanent solution available.

[old///MFanatic]

Well between those two, both have their uses and limitations.
Depending on what you're trying to do an arguement could be made on each.
The structural foam was only intended to be used for cracks less than 20mm. It kinda held the flexing down internally on that mounting block. It was fairly easy to do comparatively.
The plates along with the new tack welds was more for larger cracks, torn metal and shoring up the mounting blocks. Much more work involved.

As already mentioned the VinceBar is a better overall fix and preventative measure.

My first E46 I had covered by BMW had the whole floor panel replaced with the newer revised edition. I made them do the structural foam also during that repair. Hope it never needed work again because they wouldn't be able to weld with the foam there.

[poss]

My first E46 I had covered by BMW had the whole floor panel replaced with the newer revised edition. I made them do the structural foam also during that repair. Hope it never needed work again because they wouldn't be able to weld with the foam there.

Another recent thread on this subject demonstrates that BMW's 'magic' foam simply transferred the forces elsewhere (wheel arches cracked) - until eventually your boot floor is ripped out...

[old///MFanatic]

Another recent thread on this subject demonstrates that BMW's 'magic' foam simply transferred the forces elsewhere (wheel arches cracked) - until eventually your boot floor is ripped out...

Yep, that was discovered a while ago and a big designing reason for Vince and his brace on the sides. Forces are going to go places, but the sides are not as susceptible like that internal mounting block in the floor cavity.

[poss]

Yep, that was discovered a while ago and a big designing reason for Vince and his brace on the sides. Forces are going to go places, but the sides are not as susceptible like that internal mounting block in the floor cavity.

Sure, but eventually it's a game of (metal fatigue) dominoes/whack a mole. All the weak points are susceptible. As CMP describes, BMW's design is inherently prone to fail.

[trudriv3r]

So will installing the plates be needed if you're doing the vincebar or CMP kit? OR can you get away with not installing the plates?

[aapilcher]

So will installing the plates be needed if you're doing the vincebar or CMP kit? OR can you get away with not installing the plates?

You need to do the underside/plates as well (CMP has an in-depth write up on topside and underside reinforcement)

SME is another good option to Vincebar and CMP: https://www.s-m-eng.com/sme

[old///MFanatic]

So will installing the plates be needed if you're doing the vincebar or CMP kit? OR can you get away with not installing the plates?

“Needed”, No. Have not seen the VinceBar design stating plates would be needed since it holds from the top across both rear mounting blocks and further along to the sides.
If the metal was cracked/highly fatigued you’d want to use the plates then. If doing as preventative you do not “need” the plates. But that’s not to say it would not be “worthwhile” to do them while in there for some.

[Ramps]

I suspect if you had a car with no cracks, welded plates on, then did the epoxy to stiffen the void, you’d never see cracks. The issue with epoxy is that once injected you can never weld anything anymore without toxic smoke and likely fire lol.

[trudriv3r]

You need to do the underside/plates as well (CMP has an in-depth write up on topside and underside reinforcement)

SME is another good option to Vincebar and CMP: https://www.s-m-eng.com/sme

Thank you. That makes sense.

[trudriv3r]

“Needed”, No. Have not seen the VinceBar design stating plates would be needed since it holds from the top across both rear mounting blocks and further along to the sides.
If the metal was cracked/highly fatigued you’d want to use the plates then. If doing as preventative you do not “need” the plates. But that’s not to say it would not be “worthwhile” to do them while in there for some.

I get what you're saying.

[poss]

“Needed”, No. Have not seen the VinceBar design stating plates would be needed since it holds from the top across both rear mounting blocks and further along to the sides.
If the metal was cracked/highly fatigued you’d want to use the plates then. If doing as preventative you do not “need” the plates. But that’s not to say it would not be “worthwhile” to do them while in there for some.

The real conundrum here is "do you have any cracks?" - because to do a proper inspection you must drop the rear subframe and inspect under the mounts, and if you are going to that much trouble you might as well weld some underside plates in anyways.

It would be rare for an M3 not to have some cracking. My M3 vert with only 40K miles had cracks in the usual places - rear left subframe mount - you need to clean the area around this subframe mount as the cracks can be hairline (they are stress fractures), but the cracking emanates from the gusset spot welds under the mount.

If you have cracking you need to fix them. A topside bar and rail plates will stop them coming back or spreading elsewhere. Underside plates or that diabolical foam do not.