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      07-12-2019, 10:24 AM   #1
crowtrobot
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N51 Oil Pan Swap - Manual vs Auto

I dropped my oil pan last week to install a new gasket, as the old one had a growing leak on the passenger-side rear, and had sprouted a couple more over time. Was losing about a quart of oil every 1500mi (with track driving).

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Had some pretty bad rust around the level sensor and a few other places, and a bunch of the paint protection pulled off when I removed the gasket, so I sanded the bad areas down to the metal and sprayed some high-heat Rustoleum to seal it.

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Repair was going well until one of the studs holding the oil level sensor snapped when I was torquing it down (at 30in-lb!).

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Apparently, the oil pan on N51/N52s differs between automatics and manuals - the autos got an aluminum pan 11137552414, while the manuals (like mine) got a stamped steel pan 11137553164.

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Unfortunately, my speed shop said that the steel was too thin to guarantee that a new stud would not leak, and even worse, the stamped steel pans are impossible to come by second-hand. New OE is $700+, and new OEM are $1600 for some reason...

I was able to source an aluminum pan from an auto for $150. However there are some differences:

These pans take the same gasket, but the aluminum pan is constructed a little differently, and has a large rear face which requires longer bolts. The auto bolt kit is 11132210959, and the manual kit is 11130396707.

EDIT: There is also an extra opening on the pan, which I believe is to allow for a crankcase vent return line, but my car doesn't have the line, so there is another drainplug made of plastic, part: 11137553165

I also found when attempting to install the new pan, that the cover plate over the bell housing of the transmission is different between the two. As mentioned, the auto oil pan has a rear face that butts flat against the bell housing, and there are three bolts that go through the bell housing to secure the oil pan against it, and hold the cover plate in position. These three bolts exist on the manual as well, but to hold the cover plate in position, the plate has three threaded nuts either cast or pressed into the plate. These nuts are about 1/4" thick, and interfere with the rear face of the aluminum pan.

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My plan is to grind these nuts off, as the bolt holes line up from the transmission to the new oil pan, so I do not foresee any more issues. Will update the thread once it's all together. Lots of pain for a simple snapped stud...

Last edited by crowtrobot; 07-15-2019 at 01:30 PM..
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      07-13-2019, 09:32 AM   #2
ShocknAwe
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Weight difference? Nice find.

Wonder what the differences are between the pans on 51/52 and 54/55.
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      07-13-2019, 09:11 PM   #3
MINIz guy
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Nice work!

Did you need the disconnect the steering shaft from the rack to drop the pan? Looks like you didn't.
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      07-14-2019, 11:43 AM   #4
crowtrobot
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Quote:
Originally Posted by ShocknAwe View Post
Weight difference? Nice find.

Wonder what the differences are between the pans on 51/52 and 54/55.
Actually the aluminum pan is heavier by a kg or so. The necessity for the aluminum pan was based on the lack of availability for the steel pan, and also as you can see from the pics, the steel rusts over time.

Quote:
Originally Posted by MINIz guy View Post
Nice work!

Did you need the disconnect the steering shaft from the rack to drop the pan? Looks like you didn't.
I did not have to disconnect the steering shaft. Just used an engine brace to hold the engine up, removed the subframe bolts, the engine mount bolts, and freed up the power steering and heater lines. Used this DIY here: https://www.e90post.com/forums/showt...t=cross+thread was super helpful.

I was finally able to get this thing in yesterday. Those stupid nuts were steel pressed into the aluminum guard plate, so I found it was easier just to cut notches around the nuts and fold back the tab to break it off.

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Once they were cut off, I used some liquid gasket to help the seal and threw the new gasket on.

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To install, it's just a matter of using the three bolts joining the bell housing to the back of the oil pan to draw the oil pan into position to bolt it to the engine. It's a bit tricky to make sure the gasket stays lined up the whole time, the tolerances are pretty tight. I threaded a couple bolts in loosely, and shifted the gasket around, placed another bolt to hold it in position, repeat until everything's in place. The auto bolt kit mentioned above comes with 23x short bolts, 7x long bolts, and 3x medium bolts. The three medium bolts are meant to bolt the oil pan to the bell housing, but I had to re-use the steel ones already on the car, as these aluminum bolts were probably a cm too long. This worked out well, as there were several places the long bolts should have gone that were also too shallow for the long bolts, so I subbed in the medium ones.

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I torqued everything to 6ft-lb, plus a little, but did not do the full extra 90* called for by the torque spec, I was a little too nervous after breaking the stud to go much further. Going to run the car a while and monitor and see how it holds up, can always torque it a little more.

Hope this helps anyone caught in this position in the future, was an awful lot of trouble for a simple broken stud...
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      07-14-2019, 12:46 PM   #5
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Quote:
Originally Posted by crowtrobot View Post
Actually the aluminum pan is heavier by a kg or so. The necessity for the aluminum pan was based on the lack of availability for the steel pan, and also as you can see from the pics, the steel rusts over time.


I did not have to disconnect the steering shaft. Just used an engine brace to hold the engine up, removed the subframe bolts, the engine mount bolts, and freed up the power steering and heater lines. Used this DIY here: https://www.e90post.com/forums/showt...t=cross+thread was super helpful.

I was finally able to get this thing in yesterday. Those stupid nuts were steel pressed into the aluminum guard plate, so I found it was easier just to cut notches around the nuts and fold back the tab to break it off.

Attachment 2098970

Once they were cut off, I used some liquid gasket to help the seal and threw the new gasket on.

Attachment 2098971

To install, it's just a matter of using the three bolts joining the bell housing to the back of the oil pan to draw the oil pan into position to bolt it to the engine. It's a bit tricky to make sure the gasket stays lined up the whole time, the tolerances are pretty tight. I threaded a couple bolts in loosely, and shifted the gasket around, placed another bolt to hold it in position, repeat until everything's in place. The auto bolt kit mentioned above comes with 23x short bolts, 7x long bolts, and 3x medium bolts. The three medium bolts are meant to bolt the oil pan to the bell housing, but I had to re-use the steel ones already on the car, as these aluminum bolts were probably a cm too long. This worked out well, as there were several places the long bolts should have gone that were also too shallow for the long bolts, so I subbed in the medium ones.

Attachment 2098972

I torqued everything to 6ft-lb, plus a little, but did not do the full extra 90* called for by the torque spec, I was a little too nervous after breaking the stud to go much further. Going to run the car a while and monitor and see how it holds up, can always torque it a little more.

Hope this helps anyone caught in this position in the future, was an awful lot of trouble for a simple broken stud...
Hey crowtrobot , thanks for this writeup. I have a similar issue with rot on my steel (6MT) oilpan that I just recently found. Auto oil pans are easier to source used and come at that price point you posted. I did see 6MT bnew ones on getbmw for about $650+ I didnt know if you checked there. I would also prefer an Al oil pan to not worry about rust again. Would indys give it a go like you did, knowing it isnít compatible? Probably. Just that swapping oil pans is most likely out of my DIY league.

Update us of any leak that occurs.
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      07-15-2019, 07:34 AM   #6
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Quote:
Originally Posted by $iriu$black View Post
Hey crowtrobot , thanks for this writeup. I have a similar issue with rot on my steel (6MT) oilpan that I just recently found. Auto oil pans are easier to source used and come at that price point you posted. I did see 6MT bnew ones on getbmw for about $650+ I didnt know if you checked there. I would also prefer an Al oil pan to not worry about rust again. Would indys give it a go like you did, knowing it isnít compatible? Probably. Just that swapping oil pans is most likely out of my DIY league.

Update us of any leak that occurs.
I dunno if an indy would do it - guess it depends on your relationship with them. I've never had great luck getting a shop to fit non-standard parts, as they tend to not want to be responsible if something goes wrong.

I normally buy my parts from getbmw, but for some reason didn't look for the oil pan there. That's a little bit better than the $700+ I was finding, but still pretty annoying. If that stud hadn't broken, I'd have been satisfied sanding down the existing pan and putting some Rustoleum on. It looked pretty nice afterwards, and honestly, the steel pan is a little lighter and easier to fit, so I'd stick with the steel if you have it.

Ran the car for 15 min or so yesterday, seems like it's holding. Real test will be August once it's seen some track time.
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      07-15-2019, 08:02 AM   #7
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I like the idea of an aluminum pan too, mine is steel. But does the outlet come sideways, horizontal, like my ex-wife's? Mine is vertical which makes oil changes easier. Not a killer but I had to make up a deflector (out of scrap cardboard) to minimize the mess.

I wonder if the modification to fit the aluminum pan is less work than fixing the broken stud in the steel pan. I think I would drill out the broken stud, put a bolt in, then weld or braze the bolt in place. I have a welder but am not-so good with it. I am confident I could stick it in place but so-so on whether it would leak. Brazing is easier and probably plenty strong. Welding a thicker piece like a bolt head to a thin piece, like the pan, is entirely possible. But you have to use the settings for the thin piece. The depth of weld into the bolt head will be slight but my main concern would be leaking oil. The weld only has to stop the bolt from rotating.

Thanks for a nice piece.
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      07-15-2019, 12:46 PM   #8
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Quote:
Originally Posted by JimD View Post
I like the idea of an aluminum pan too, mine is steel. But does the outlet come sideways, horizontal, like my ex-wife's? Mine is vertical which makes oil changes easier. Not a killer but I had to make up a deflector (out of scrap cardboard) to minimize the mess.

I wonder if the modification to fit the aluminum pan is less work than fixing the broken stud in the steel pan. I think I would drill out the broken stud, put a bolt in, then weld or braze the bolt in place.
Thanks for a nice piece.
My original plan was to just have a shop drill out the stud and weld a new one in just as you suggest. I took it to VAC Motorsport and they said that they were not confident a new stud wouldn't leak due to the thickness (or lack thereof) of the stamped steel. They have a fantastic fabrication facility, and make high quality product, so I'd trust their judgement when it came to patching up this issue. I don't have the tools or ability to try it on my own, so I went the replacement route.

The drain plug on the new pan does indeed go sideways, which is unfortunate. I usually take the whole belly pan off anyway, so it's not a huge difference, but pointing down would definitely be better.
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