[TheGoodTheBadTheUgly]

Hello all, I will try to make this short.

I was looking to get a project E90 N55 to build the engine and put a large single turbo to be within the realm of 600-800 hp still unsure.

I live in Canada, so I don't buy stuff that isn't xDrive, anyways now with xDelete I can switch from AWD to RWD, but that is besides the point.

I found, for a great price, a 335i xDrive with a manual transmission and am keen on getting this for the build since so far I have only owned automatic N55s.

The problem is I have read a lot and the synchronizer gears (for gear 2 and 3 usually) in the N55 manual transmission sustain too much load, and especially on AWD models, and go bad.

Since I will have the engine and transmission out to do a complete rebuild, I was thinking if there was a way to upgrade these synchronizers to something that can withstand the power band I will try to achieve.

I also seen some people switching to a N54 manual transmission that don't seem to have the same synchronizer issue.

Or should I just drop the whole idea?

[oVeRdOsE.]

N55 are solid they can hold quite a lot of power.
Mine is stock (has a jb+), but 170k km, and I put 0$ on it, all OEM. Still running good.

- crank bolt capture kit
- upgraded rod bearing and you're good to go.

On FB market there a lot of N55 equipped BMWs with non running engine, mainly rod bearings, so do all the critical item on it, since it's hard and expensive find a N55 in shape to replace it.

For the transmission, I would try, Ive change my busted transmission and it wasnt that hard and not that expensive, I wouldnt drop the project for that.

Use good oil, like redline MTL and a magnetic plug. Get a nice shifter to avoid money shifts or grinding.

[TheGoodTheBadTheUgly]

Originally Posted by oVeRdOsE.

N55 are solid they can hold quite a lot of power.
Mine is stock (has a jb+), but 170k km, and I put 0$ on it, all OEM. Still running good.

- crank bolt capture kit
- upgraded rod bearing and you're good to go.

On FB market there a lot of N55 equipped BMWs with non running engine, mainly rod bearings, so do all the critical item on it, since it's hard and expensive find a N55 in shape to replace it.

For the transmission, I would try, Ive change my busted transmission and it wasnt that hard and not that expensive, I wouldnt drop the project for that.

Use good oil, like redline MTL and a magnetic plug. Get a nice shifter to avoid money shifts or grinding.

Yeah I am not too worried about the engine since I will be building it with some pretty nice forged components and have been reading about things done to N55s for years.

It's more the manual transmission that is uncharted territory for me, so I appreciate the input!

[oVeRdOsE.]

they said the same for the 340xi 6mt, and some doing huge power on it.

Maybe try to get a tune boost-per-gear or at least boost-per-rpm.

Avoid launch control.

And have fun on roll pulls and anti-lag pull.

[TheGoodTheBadTheUgly]

Originally Posted by oVeRdOsE.

they said the same for the 340xi 6mt, and some doing huge power on it.

Maybe try to get a tune boost-per-gear or at least boost-per-rpm.

Avoid launch control.

And have fun on roll pulls and anti-lag pull.

Fair enough, I will take this into consideration! I am most likely being over-cautious but can't change how I think... in the end it's a project

[BMW Guy]

Originally Posted by oVeRdOsE.

N55 are solid they can hold quite a lot of power.
Mine is stock (has a jb+), but 170k km, and I put 0$ on it, all OEM. Still running good.

- crank bolt capture kit
- upgraded rod bearing and you're good to go.

On FB market there a lot of N55 equipped BMWs with non running engine, mainly rod bearings, so do all the critical item on it, since it's hard and expensive find a N55 in shape to replace it.

Do the rod bearings really need to be done on an N55 like mine?(See my mod list below) It has 100k on it. Isn't the issue oil starvation and not the actual rod bearings? Would it be a better idea to replace the oil sump like the s55 one?

[fastboatster]

Originally Posted by BMW Guy

Do the rod bearings really need to be done on an N55 like mine?(See my mod list below) It has 100k on it. Isn't the issue oil starvation and not the actual rod bearings? Would it be a better idea to replace the oil sump like the s55 one?

yes, definitely replace the rod bearings at 100kmiles, they are not that difficult (or expensive) to do when doing the oil pan. Nobody can tell for sure what's causing them to sometimes wear out very quickly even on stock cars, likely there're many reasons.

[BMW Guy]

Originally Posted by fastboatster

yes, definitely replace the rod bearings at 100kmiles, they are not that difficult (or expensive) to do when doing the oil pan. Nobody can tell for sure what's causing them to sometimes wear out very quickly even on stock cars, likely there're many reasons.

The oil pan gasket was replaced 10k miles ago by the previous owner so I couldn't have done it then. Have you actually owned a car with the n55? I'm asking because from what I've seen, this topic is VERY controversial and everybody has a different opinion about it so I only want the opinion of someone who has owned a n55. I feel like this issue is almost as controversial as the discussion of whether the N54 is horribly unreliable or not.

[fastboatster]

Originally Posted by BMW Guy

Have you actually owned a car with the n55?

The fact that I didn't put my 2011 335i into my profile or signature doesn't mean I haven't had it for 2 years. I replaced the oil pan gasket and rod bearings first thing when I got it with 108 kmiles. Bearings weren't the worst, but definitely had some wear. Car was stock before I got it.
That's your car, though, so it's up to you if you want to do it or not. I've seen 200+ kmile f10 535i's on fb market place which never had rod bearings done but managed to do all these miles, and I have seen 80kmile e90 335i's with rod knock. Almost like a lottery

[oVeRdOsE.]

Originally Posted by BMW Guy

Do the rod bearings really need to be done on an N55 like mine?(See my mod list below) It has 100k on it. Isn't the issue oil starvation and not the actual rod bearings? Would it be a better idea to replace the oil sump like the s55 one?

yes rod bearing fail due to oil starvation (or more like less oil than design) and high rpm, but not much you can do about it unless you change oil pump and add baffles, or straight dry sump.

It's more common on N55 than N54 , but surely not has common like on S65.

Local well respected VAG mech here (doing mainly high end cars), got a lot of N55 engine swap request lately and rod bearing replacement. He's buggin me to do mine asap as preventive.

He did my N54 one at 65k miles, by prevention, since I was going for 600hp.

However my N55 is on a Zf8, wife driven and cancelled the start-n-stop fuel saver aka rod bearing killer, and liquimoly every 8k km, so I dont ''Feel'' like doing this soon

[TheGoodTheBadTheUgly]

Originally Posted by BMW Guy

Do the rod bearings really need to be done on an N55 like mine?(See my mod list below) It has 100k on it. Isn't the issue oil starvation and not the actual rod bearings? Would it be a better idea to replace the oil sump like the s55 one?

Ahh this again...

Over the last few years I have participated to quite a few different threads that were touching upon this issue.

After a lot of rambling and going in circles, its concluded that we don't know much more that it is oil starvation related and might have to do with the way oil is picked up in the pan.

I personally never bothered with changing the rod bearings and I was quite over 180k km. Quite honestly I also wasn't the type to baby the car when I was driving it but I was always on top of things when it came to oil change. I used to also take oil samples and send them to the lab for analysis at some point.

Never had an issue with rod bearings on both of my N55s (fingers crossed it continues that way with the X1) but this was not the case for many others.

I don't agree that it is "not that difficult" to change the rod bearings. Sure the process is straightforward but there is still many steps and lots of them are critical as in you could make things worse than they were. Definitely is a job that's doable even without a lift. Maybe it's my xDrive bias talking since this damn subframe always complicates everything, but I stil feel like its a very involved job.

[BMW Guy]

Originally Posted by TheGoodTheBadTheUgly

Ahh this again...

Over the last few years I have participated to quite a few different threads that were touching upon this issue.

After a lot of rambling and going in circles, its concluded that we don't know much more that it is oil starvation related and might have to do with the way oil is picked up in the pan.

I personally never bothered with changing the rod bearings and I was quite over 180k km. Quite honestly I also wasn't the type to baby the car when I was driving it but I was always on top of things when it came to oil change. I used to also take oil samples and send them to the lab for analysis at some point.

Never had an issue with rod bearings on both of my N55s (fingers crossed it continues that way with the X1) but this was not the case for many others.

I don't agree that it is "not that difficult" to change the rod bearings. Sure the process is straightforward but there is still many steps and lots of them are critical as in you could make things worse than they were. Definitely is a job that's doable even without a lift. Maybe it's my xDrive bias talking since this damn subframe always complicates everything, but I stil feel like its a very involved job.

My oil analysis showed all clear though I know that those aren't always accurate for detecting potential rod-bearing failure.

[TheGoodTheBadTheUgly]

Originally Posted by BMW Guy

My oil analysis showed all clear though I know that those aren't always accurate for detecting potential rod-bearing failure.

Indeed these are nice to see some slow contamination and accelerates wear of parts but a catsstrophic failure such as spun rod bearings happens instantly and woukd probably not be foreshadowed/predicted by oil analysis.

[oVeRdOsE.]

well you have 3 sources

- internet talk shit
- vag shop and dealers
- your experience.

I might add the numbers of cheap bmw on sale on market with a non-working n55 engine.

when vag shop owners tell me this is not uncommon, I take my precaution. 1 owner also told me sometimes the cranckshaft is savable if the bearing are not welded, most of the time is cyl 5 and 6.
on my stock n55, i dont think ill do it.

on a fun modded car, ill do 100%, is not ''that'' expensive.




For the transmission have you more info? I might add to keep a dual mass flywheel and keep the clutch delay valve.