Reinforcement plates vs structural foam ?

[poss]

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.

Unfortunately your suspicions would be incorrect - as another member with the epoxy foam injection recently attested to - The cracking moved to his wheel arches. Epoxy foam injection is not a lasting fix. You'd have to have rocks in your head to do it to your car given that it severely curtails proper repair options.

[old///MFanatic]

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.

I see your reasoning but one only needs to “lower” the subframe marginally to have access to clean and inspect. Done inspections many times over the decade plus. You don’t need to fully “drop” it/remove it like when doing plates. I don’t feel the inspection time is close to being equivalent to the repair time when welding in plates. Heck you have to drop the gas tank to do the welding responsibly. Not to mention disconnecting driveshaft and rear brake lines. It’s much more involved and not something I’d consider doing as an “already in there” time saving overlap.

[AussieE46M3]

“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.

Plates are still entirely needed regardless of the topside reinforcement as the front two mounts are still prone to fail underneath. Technically the rear two mounts don't once you've done enough up top however, if you're doing the front two, the rear two aren't optional unless you want to subframe to sit funny.

Every M3 I've ever inspected has had cracks present so they're more or less always needed for the purpose of strengthening the fatigued steel to prevent the same cracks from forming again at the stress concentrations.

Something to keep in mind is that a good enough set of underside plates provides almost as much rigidity as most of the slender hidden bar solutions as they have just much material equally as far from the neutral axis. When you pair them with a set of chassis rail to RACP plates you yield more or less the same result at a more budget friendly price.

[old///MFanatic]

Plates are still entirely needed regardless of the topside reinforcement as the front two mounts are still prone to fail underneath.

The VinceBar kit does the fronts also. Like the rears it makes it so the bolts go down through the reinforcement design. So instead of pulling down from under the bottom sheet metal cracking it, it holds the "mounting block" from above the top layer of sheet metal.
I would not say the plates are "needed" in addition, especially on a "preventative" install. Different for a torn metal area, or perhaps if it's a drift car. That's just my opinion. I'm just stating why, your opinion may vary. I'm completely open to new info. Been researching this stuff over 14 years and the first idea behind the fix being one from Active Autowerks using a bolt-thru idea with large washers.

[old///MFanatic]

Wow, to give an idea what I was talking about here is that idea (I saved Photobucket) in a very very quick draw showing the theory. Yep, that was over 14 years ago in 2006 we were discussing this. Years before BMW had the Voluntary Inspection/Recall.

[AussieE46M3]

I understand how a top nut can prevent the top welds from tearing out in the earlier cars however, the later cars had additional welds securing the threaded insert within the chassis and thus the inserts no longer tore out.

I've seen a few people say that the stud gets bent left to right and that is the result of the cracking underneath however, the front subframe mounts are secured in double shear so the stud doesn't have the ability to flex side to side? There still would be lateral loading on the insert with some eccentricity could cause the top welds to fail. Cracks grow perpendicular to stress and cracks seem to form at the top and bottom of the top welds so would suggest this could be the cause.

My concern is simply that cracks form around the stud hole due to what I assume to be the contacting pressure. You don't need a substantial plate in this case (provided you've reinforced from above) as it needs to only function like a large washer. I personally would go for a larger plate as I do see cracks creep along the radius and would prefer to be a bit more comprehensive.

This also assumes you're using a non standard bush which is known to lunge into the chassis which also requires a plate to increase thickness and thus shear strength of the underside face.

Cracking at the front mounts is also a lot more complex than just the top welds and underside. You'll find cracks around the threaded anchors under the back seat and spot weld failure where the bench seat base meets the frame rail and in extreme cases where the front edge of the RACP meets the seat base under the sound deadener.
A bolt through design does nothing for these areas nor does a tube linking the bench seat to the mount IMO.

Check out figure 19 onwards if you want examples of what I'm referring to: https://cmpautoengineering.com/pages...ubframe-mounts

[M3AT]

I've heard shops won't even consider welding plates in if you've already done the foam because of how flammable the foam is.

[old///MFanatic]

Cracking at the front mounts is also a lot more complex than just the top welds and underside. You'll find cracks around the threaded anchors...

Thank you, plausible points. Will look into that more.
As of now not convinced on plates being necessary.

I knew in your earlier post just being aware that the plates raise the chassis and change alignment you were informed more than most(and that’s is a tiny part of this complex fix). I enjoy the discussion and appreciate your sharing of thoughts sir.

[poss]

I see your reasoning but one only needs to “lower” the subframe marginally to have access to clean and inspect. Done inspections many times over the decade plus. You don’t need to fully “drop” it/remove it like when doing plates. I don’t feel the inspection time is close to being equivalent to the repair time when welding in plates. Heck you have to drop the gas tank to do the welding responsibly. Not to mention disconnecting driveshaft and rear brake lines. It’s much more involved and not something I’d consider doing as an “already in there” time saving overlap.

As CMP say on their website, all E46's RACPs will eventually fail due to metal fatigue (except for the compact). It's not a matter of if but when - so I would have pre-emptively reinforced mine even if there was no sign of cracking. I'd prefer to fix the problem rather than having to keep lowering the subframe to inspect on a regular basis - and then one day discovering a crack and having to do it anyway - and your probably much better off dealing with it before your RACP is weakened to the point of cracking.

[old///MFanatic]

As CMP say on their website, all E46's RACPs will eventually fail due to metal fatigue. It's not a matter of if but when - so I would have pre-emptively reinforced mine even if there was no sign of cracking. I'd prefer to fix the problem rather than having to keep lowering the subframe to inspect on a regular basis - and then one day discovering a crack and having to do it anyway - and your probably much better off dealing with it before your RACP is weakened to the point of cracking.

Yes that is fair.
On the other part, CMP has been around some 4-5 years total. Back in late 2005 I'll admit I too have posts in forums with this exact same thought that they all were going to crack over time. But 15 years later I have found that's just not the case. Sure there are issues but it's not a given to have catastrophic damage. BMW produced over 4 Million E46s. Go ask any BMW dealership or shop if even 1/4 E46s they have seen in (would be around a million E46s) have failed subframe mounting points that must to be fixed. The 3rd revision panel was even better than than the 2nd one. But yes they absolutely can fail, I'm not saying they don't just to be clear.
Back to your earlier statement about just doing plates if you're going to take time to inspect. That's not a job I would ever mandate to friend/customer when they can Never have an issue in their ownership lifetime. If time and cost weren't a factor then sure, everyone gets free reinforced bullet-proof floors, new rods, vanos units and every bushing on car. But for most there is a cost-to-risk factor that must be examined and determined. And since you quoted them before, with respect here's another CMP statement on topic, "What is necessary really comes down to each individual owner’s long term plans and goals for their vehicle. Not all customers can justify a complete top to bottom reinforcement on their cars and we don’t always encourage that "

[poss]

What is necessary really comes down to each individual owner’s long term plans and goals for their vehicle. Not all customers can justify a complete top to bottom reinforcement on their cars and we don’t always encourage that [/I][/COLOR]"

Agree. I was speaking from my personal perspective - not for everyone. I have a low mileage car in pristine condition that I plan to keep for the foreseeable future. I would have preventatively dealt with it even without any visible cracking - however, even my low mileage never-tracked 'vert had cracks. The CMP dude says every M3 he is now seeing has them, and I recall a UK shop saying some time back that every CSL they inspected had the issue.

If you're regularly lowering the subframe to diligently clean and check for hairline cracks then, by all means feel free to wait until the issue actually manifests if that's your plan - but we've seen over the years that the first time many owners become aware is when the issue has become quite advanced and expensive to repair (and even dangerous).

I tend to side with CMP's reasoning on this - fundamentally, the design of the RACP cannot withstand fatigue failure. Sure BMW has made some tweaks to prevent failure within the warranty period, but in the end it all comes down to the number and severity of duty cycles applied to the RACP. If you baby your M3 or mainly do highway cruising then the metal fatigue will take longer to manifest, but if you track or have a lead foot your RACP will fail much sooner.

Personally, I didn't buy an M3 to baby it :-)

[MarcoPolo]

maybe i missed a response to this question, but for those that already have the foam injection (like myself), what options exist. mine is an '06 fwiw and it was foamed prior to purchase. it has been inspected numerous times w/no cracks discovered. since reinforcement plates can't be done, will the foam with vincebar be sufficient?

thanks.

[ATB88]

maybe i missed a response to this question, but for those that already have the foam injection (like myself), what options exist. mine is an '06 fwiw and it was foamed prior to purchase. it has been inspected numerous times w/no cracks discovered. since reinforcement plates can't be done, will the foam with vincebar be sufficient?

thanks.

You can do plates, just epoxied rather than welded.

[mrgizmo04]

Just to clarify, because I don't think everyone knows/realizes, AussieE46M3 is CMP, he frequents the forums and helps the community.

Sent from my SM-G950U using Tapatalk

[old///MFanatic]

Just to clarify, because I don't think everyone knows/realizes, AussieE46M3 is CMP

I literally just figured that out five minutes ago as I sent CMP an email. 🤦🏻♂️
Thanks for the clarification haha.
I do like your top mount kit pricing. 👋🏻 AussieE46M3