35i downpipes/cats install Help needed

[keving1]

I am about to change the downpipes/cats on my 35i, are there are guides/videos specific to the 35i on how to do this? Everything on the net seems to be 335i/135i and seems different to the 35i, for example do I have to move the steering rack?

Any help appreciated.

Thanks

 

[keving1]

Can anyone help as I plan to try to do this today.

Do I have to move the steering rack and is the install the same as the 335i/135i?

 

[john-e89]

Can anyone help as I plan to try to do this today.

Do I have to move the steering rack and is the install the same as the 335i/135i?

I gather it’s a pig of a job space wise Kev, are you sure you want to get into it not knowing the full picture yet..?

 

[keving1]

Thanks John for the reply, my zed is on axle stands at the moment and I have had a look at the job and yes it is tight.

Does the steering rack need to be removed as in the 335i/135i or does it stay in place?

 

[john-e89]

Thanks John for the reply, my zed is on axle stands at the moment and I have had a look at the job and yes it is tight.

Does the steering rack need to be removed as in the 335i/135i or does it stay in place?

I’m pretty sure you can leave it in place Kev if you’ve got plenty of room underneath to twist the pipes out. It’s more a case of finding the right angle to pop them free which they do if you have patience. Best of luck, let us know how you get on and hopefully not too many skinned knuckles.....there will be some but keep calm and don’t let it rag you..! :lol:

 

[mcbutler]

You need to drop the front subframe, it's not a great DIY job you will really struggle with it. The downpipes will be extremely close to the subframe and when you finish and you may have to loosen them again to reposition.
If you don't get it right you will get constant exhaust blows from misaligned flanges

 

[sunnydays]

Darren Woods did mine in less than 3 hours. RE92 did his install diy. His post below

I wouldn't trust any old garage with the install. It's a real s**t of a job with plenty of opportunities for mistakes. Personally I'd only trust the likes of Darren Wood or Birds with this job.

I went for the DIY option. The install was probably around 8 hours. I then realised that one pipe was touching the subframe causing a rattle and my vband clamps weren't on correctly. The second time around it only took 3 hours. It's pretty horrible without a lift, lots of scraped skin and swearing involved.

The common install problems are:
-vband interfering with wastegate actuator
-leaks from vband or gasket
-O2 sensors getting either damaged or replaced in the incorrect places
-pipes touching the engine mount heat shield or subframe

The right-hand drive Z4 install is probably the most tricky of any downpipe install for a N54 engine, there's not a lot of room and you have to be really aware of clearances to avoid rattles.

 

[R.E92]

I didn't drop the subframe but it may have saved me time and skin. I just unbolted the steering rack and moved it forward (just 2 bolts)

The trickiest bit of the whole job is getting the vband clamp to seat and tighten correctly on the rear turbo. You have to do it from above but you only have visibility of the band from below so manoeuvring it is just torture. I have big hands so they don't really fit between the steering column and the engine well.

It's the perfect time to have a go at a job like this but make sure to have plenty of axle stands and other objects under the car to avoid crushing yourself because you'll be spending a lot of time flat on your back completely under the car.

I really didn't take good notes when doing the job but the only tools you need outside of the usual socket set would be a stubby 22mm ratchet spanner, there is a special BMW tool for removing the O2 sensors but I managed by using a stubby spanner. You also need a 13mm socket on a long extension to get to the clamp from the top, I have a couple of 1/4" socket sets and had to use all 3 extension bars to get it far enough.

 

[john-e89]

Any updates on progress so far Kev..?

 

[keving1]

I didn't drop the subframe but it may have saved me time and skin. I just unbolted the steering rack and moved it forward (just 2 bolts)

The trickiest bit of the whole job is getting the vband clamp to seat and tighten correctly on the rear turbo. You have to do it from above but you only have visibility of the band from below so manoeuvring it is just torture. I have big hands so they don't really fit between the steering column and the engine well.

It's the perfect time to have a go at a job like this but make sure to have plenty of axle stands and other objects under the car to avoid crushing yourself because you'll be spending a lot of time flat on your back completely under the car.

I really didn't take good notes when doing the job but the only tools you need outside of the usual socket set would be a stubby 22mm ratchet spanner, there is a special BMW tool for removing the O2 sensors but I managed by using a stubby spanner. You also need a 13mm socket on a long extension to get to the clamp from the top, I have a couple of 1/4" socket sets and had to use all 3 extension bars to get it far enough.

Thanks for the advice R.E92 it has been helpful, did you remove both the front sensors before removing the downpipe and did you replace the gaskets on the turbo to downpipe joints or leave the existing ones in place?

Other things have got in the way over the last week so I haven't been able to do anymore on this but hopefully will have a full day tomorrow to crack on with it.

 

[R.E92]

I didn't drop the subframe but it may have saved me time and skin. I just unbolted the steering rack and moved it forward (just 2 bolts)

The trickiest bit of the whole job is getting the vband clamp to seat and tighten correctly on the rear turbo. You have to do it from above but you only have visibility of the band from below so manoeuvring it is just torture. I have big hands so they don't really fit between the steering column and the engine well.

It's the perfect time to have a go at a job like this but make sure to have plenty of axle stands and other objects under the car to avoid crushing yourself because you'll be spending a lot of time flat on your back completely under the car.

I really didn't take good notes when doing the job but the only tools you need outside of the usual socket set would be a stubby 22mm ratchet spanner, there is a special BMW tool for removing the O2 sensors but I managed by using a stubby spanner. You also need a 13mm socket on a long extension to get to the clamp from the top, I have a couple of 1/4" socket sets and had to use all 3 extension bars to get it far enough.

Thanks for the advice R.E92 it has been helpful, did you remove both the front sensors before removing the downpipe and did you replace the gaskets on the turbo to downpipe joints or leave the existing ones in place?

Other things have got in the way over the last week so I haven't been able to do anymore on this but hopefully will have a full day tomorrow to crack on with it.

I think I had to remove them to get the pipes out. Makes sure you get some tape and label which sensors come out of which holes, mixing them up is really common. Be very careful with them, they aren't fragile but I think if you dropped them on the floor it could possibly ruin them.

I didn't even know about the downpipe to turbo gasket until I'd finished the job, apparently it commonly gets stuck on the turbo side and most people re-use it. All of the DIY guides I saw didn't even mention them so I'm assuming it's OK. I think if I were to do it again I'd want to replace them for the sake of it.

 

[R.E92]

Also another couple of things to note.

Once the stock pipes are removed you need to remove the bracket that holds them in place and also replace one of the bolts around the transmission. The pipes should come with a spare flat headed version of the bolt to replace it with along with the usual fitting kit.

The bracket and original bolt look similar to this (photo is from a 5 series install):

 

[R.E92]

How did you get on?

 

[keving1]

How did you get on?

It took me quite a few hours over 2 days but all the help on here got me through

I eventually moved the steering rack forward and removed the small heat shield over the bottom of the steering column. The removal of this shield allows far better access and was now able to get a hand in and up either side of the downpipes.

Also took both downpipes out complete with Lambda sensors as the first one I tried to remove was stuck fast. Fairly easy to manuver these in & out and the sensor came out with a sensor wrench.

Taking them off took longer than getting it all back together as the learning going through the process makes it a lot easier and quicker. I reckon I could now do the whole thing in 4 hours or less

On to the next jobs - intake valves cleaning & fitting H&R front and rear anti roll bars when I get them.

 

[R.E92]

How did you get on?

It took me quite a few hours over 2 days but all the help on here got me through

I eventually moved the steering rack forward and removed the small heat shield over the bottom of the steering column. The removal of this shield allows far better access and was now able to get a hand in and up either side of the downpipes.

Also took both downpipes out complete with Lambda sensors as the first one I tried to remove was stuck fast. Fairly easy to manuver these in & out and the sensor came out with a sensor wrench.

Taking them off took longer than getting it all back together as the learning going through the process makes it a lot easier and quicker. I reckon I could now do the whole thing in 4 hours or less

On to the next jobs - intake valves cleaning & fitting H&R front and rear anti roll bars when I get them.

Great news

How are you finding the change? The faster spool made it all worthwhile for me, it was fast before but the boost comes on so much faster now.