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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sat, Oct-22-2016, 01:26:07 AM   #1
///MonkeyTech
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Default subframe crack and reinforcement information

Hi, so I'm pretty new to this forum, but I have had 5 years experience doing various subframes for street, track, and monster hp vehicles on over 30 e46 m3s. I thought I wouild like to shed a little light on the subject. I will post pictures on my next post.

First off I would like to let people know they are chassis cracks, not subframes. These plates adda bit more material to reinforce the thinner layers of sheet metal that were spot welded together. A good example is the e36 factory chassis. It has 4 plates where the subframe meets the chassis. These plates are stitch welded in 4 plates about 1/2" long, not much. By doing so, I rarely ever heard of e36 having problems. Another good example is the e46 e36 front strut reinforcement. This plate is not even welded to the chassis, just sandwiched between the chassis and the strut mount. With these reinforcements, the cracks never start.

A crack on the sheet metal chassis can be considered like a crack on glass, except with a quality penetrating weld, the crack can be fixed, not to mention its not visible right in front of your face like a windshield would be. I've been hearing and reading about people saying all sorts of things. My post may not be the most organized. With that being said, I would like to write what I think about some statements and questions people have had about theirs.

I heard the subframe reinforcement plates are not enough, true?
Like I mentioned about the e36, they were manufactured with very basic plates on the chassis, and I have not heard of any crack instances. I recommend ANY e46 owner to do the subframe reinforcement before any cracks start. A lot of guys have cracks in multiple areas in the chassis and send it to a shopo that might not know any better. They weld on the plates where the major cracks are. They go and weld other areas together that the kits provided do not cover. There would be a need to make custom plates to cover certain areas that were not provided by these companies. Or if it was that bad, the complete portion of the chassis purchased from bmw would need to be replaced. I've done 2 of those jobs before and it was a PIA. At this point the car is compromised.

BMW already took care of my recall, is it necessary?
Bmw replaced the floor, but replaced it with the same floor that is prone to cracking. I have a customer that faced this exact scenario. After a few more miles, it's cracking again. Subframe reinforcement plates are not a bmw, the dealer will not install them

I don't see any cracks, I don't need it!
When you see the crack, its at least 1" long. The start of the crack is hiding under the bushing. The cracks starts usually from the front right , then the back left mount. When those start to get a little worse, the chassis starts to separate near the gas tank filler neck. Then the spring perches start to fall apart, then the trunk. There is a ton of undercoating under the car, the start of the crack could be under there but you don't see it until it gets pretty bad. Remember what I said about glass cracks? PREVENTION is my point. no cracks in these starting areas, then the cracks don't spread

I have a convertible, they don't need it.
Not true, ive seen and done convertables that were cracked


I want the Reddish kit, those ones are beefy!
Again, prevention is the key word. The e36 factory subframe reinforcement are the most basic plates youll ever see. Now , if you crack starts to get pretty long over something the plate does not cover well, I can see the added benefit. Those kits require a lot of grinding and welding though, I love welding, but sometimes less welding is better. ANother note is that these are subframe reinforcements and do not make a stiffer chassis. You might want to look into bars that connect more with other areas of flex

What do you think about epoxy on the subframe reinforcements?
I wouldn't mind doing epoxy on a car that had absolutely zero cracks. I wouild say 90% of the cars I've done all had some sort of crack on it.
I drill out the ends of each crack to stop the crack, then weld the crack shut with a good penetrating weld. Overhead welding is a tad different than welding on the bench and its harder to get good penetration because gravity is pulling the weld down. Good settings on the mig with some experience has worked for me

How about tig welding the subframe?
TIG welding is good on clean metal. Even if you ground down the visible part of the subframe, you wont be able to open your chassis to grind down the back of the metal. Once you penetrate through you will get a lot of contamination. Not only is it a PIA, the mig will produce better welds in this situation. Sitting there with 20 clean tungstens, blowing holes from contamination, contaminated welds, etc etc.

Do I need the extra reinforcement bars I see guys on the forum or Mason engineering?
Those are great bars they made and engineered, but with the many subframes I have done, I have not seen cracks to reappear even with track use. I could see these bars and reinforcements beneficial for stiffer chassis as well as strengthening these weak areas. There were a few instances where I would have to turn down jobs because the severity of the cracks. I had to be honest with them and tell them either to find someone that would want to spend a week redoing the floor, sell the car, or junk it.


I can't think of anything else more right now. All I can say is STAY AWAY FROM CRACK! Avoid it before it starts. E46 is a great car besides that, vanos, and smg problems. Engines and transmissions can be fixed or replaced. A badly cracked chassis is almost like a bad accident. I wish I took more pictuers of different examples or work I have done. Feel free to comment, criticize, or questions about my post.
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Old Sat, Oct-22-2016, 02:58:15 AM   #2
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Default Re: subframe crack and reinforcement information

Thanks for sharing these thoughts. I'm looking forward to pics, especially if you have some good ones to illustrate the E36 plates you referred to.
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Old Sat, Oct-22-2016, 05:57:33 AM   #3
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Default Re: subframe crack and reinforcement information

[Img][/img]
I like to get to the cracks when they are hairline. Thus is now starting to seperate. This is past that. Picture is front right.
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Old Sat, Oct-22-2016, 05:59:11 AM   #4
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Default Re: subframe crack and reinforcement information


Left rear crack seperating.

Sorry, I didn't have the pictures of the e36 ones. I wish I had more documentation of the ones I saw, but it just became so common. These are ones I dug up
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Old Sat, Oct-22-2016, 06:07:07 AM   #5
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Default Re: subframe crack and reinforcement information

front plate welded

Front reddish kit welded. Takes a bit of tacking n hammering to get it to curve with the bends. Nice, but not exactly needed if you catch the cracks early
reddish right rear
turner or vac rear
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Old Sat, Oct-22-2016, 06:20:31 AM   #6
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Default Re: subframe crack and reinforcement information

this is an e36 front strut to that cracked and ended up welding the cracks, making a custom plate over the cracks. I added big washers to the other 2 holes for a tiny bit if strength, but mainly so there wasn't a huge height difference if he chose to do a strut bar. Underneath us the factory paste welded from the underside, that's why you see random penetration. If he would have added the plate underneath before the cracks started, I would not have had to weld it in. Reason being after welding the cracks, the weld penetrating wouldn't allow a nice flat for the payee to sit.
Everything was ground down.
Plate was bolted up
Cracks welded, at this point the penetration stuck to the underside reinforcement plate
Welded crack then ground down to allow for top custom reinforcement to sit flat
Then everything to and bottom welded, painted reinforced.

Again, my goal for this thread is to let people know we do this all to prevent cracks, and gleefully people don't leave their cars to a point they are considered salvaged
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Old Sat, Oct-22-2016, 06:23:26 AM   #7
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Default Re: subframe crack and reinforcement information

I don't mean this in a bad way, but we're way beyond what you're posting about at this point. Have you read the latest RACP related threads in this forum in the last few months? Cool pictures and anecdotes though!

Check of threads with the name Vince.
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Last edited by TboneM3; Sat, Oct-22-2016 at 06:29:22 AM.
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Old Sat, Oct-22-2016, 06:28:25 AM   #8
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Default Re: subframe crack and reinforcement information

Quote:
Originally Posted by MarcZCP View Post
Thanks for sharing these thoughts. I'm looking forward to pics, especially if you have some good ones to illustrate the E36 plates you referred to.
E36 platest look like the turner front plate. An oval plate stitch welded to the chassis.
I'm sure everyone has seen the front strut reinforcement. A strut bar and those $20 plates simply bolted on prevent cracks.
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Old Sat, Oct-22-2016, 08:45:12 AM   #9
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Default Re: subframe crack and reinforcement information

From one Monkey to another ( ), where abouts are you in Pasadena? Are you an independent like Forum Member Kaiv, or do you have/work for a shop, and if so, what's is the name? Also, that's some nice mig welding!
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Old Sat, Oct-22-2016, 03:00:00 PM   #10
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Default Re: subframe crack and reinforcement information

Quote:
Originally Posted by TboneM3 View Post
I don't mean this in a bad way, but we're way beyond what you're posting about at this point. Have you read the latest RACP related threads in this forum in the last few months? Cool pictures and anecdotes though!

Check of threads with the name Vince.
Yeah, I know everyone knows about the crack but I got a ton of these questions about subframe. I thought I would throw this post out there for people. It's come to a point where people either think they need to bulletproof their chassis, or that there is no cure to the problem because they waited so long, or people are thinking is going to stiffen the chassis for better handling, or the BEST kit, or the BEST method mig vs tig vs epoxy. I don't mean to sound arrogant, but I've seen and done a lot and thought I would share my knowledge. I know your not trying to make a negative comment.
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Discussing CMP Auto Engineering subframe kit in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)