2.5 Exhaust Downpipe joint rusty bolts replaced

colb

Senior member
Newport, South Wales UK, the home of Zedshed Cymru
The exhaust bolts on the downpipe joints had corroded away what was left of the two lower nuts were just about holding the joint together and of course the rust. The original bolts have blind splined heads that grip inside the upper joint holes and were seized in. Cut what was left of the lower end of the bolt so it was flush with the exhaust flange and gave the air hammer a go but it wouldn't shift the bolt. Ended up using a thin cutting disc in the angle grinder and cut a slot along lower and upper sides of the jointing brackets which took the tension off the splined end. A few rattles with the air hammer had them moving and out they popped. Replaced both with Stainless flanged bolts and flanged nuts put some Loctite on the threads, remains to be seen if it holds up to the heat but both nuts were fully tigtened and the joint tested leak free so the gaskets remained intact. I did fill the visible slot with exhaust paste to finish it off.
Upper bolts still have rusty nuts intact so these were left for another day, will be harder to get at these with an angle grinder may have to invest in a Dremel and give that a go.
Video by someone else doing this job but drilled them out,
https://www.youtube.com/watch?v=b8aKbU7rRf8
I tried drilling but my new drills wouldn't touch the original bolts so resorted to the angle grinder and slot method.
 

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Mine were the same. I done the gaskets last month as I had a slight blow.
I manage to knock the studs out with a hammer.
 
Nice approach colb. I’ve tackled them twice by grinding the bolt head flush like you did then drilling through with progressively bigger drill bits.
The second one I did burnt out about 20 bits. I started to think it would have been cheaper to buy an oxyacetylene torch!!
 
Don't know what grade of steel those original bolts are but my drills wouldn't make any impression on them, slotting the flanges worked a treat. Will have to do the upper two sometime using the same method of slotting.
 
I bookmarked this too - it would have come in handy when I owned my 325xi . . . . I think I only went through 4 drill bits.
 
This has been covered a number of times as its a weak point on the car. Mr Exhaust did a good job on mine and gave me a lifetime quarantee for about £180. Be careful with the gasket and make sure you get it from BMW as its the correct diameter. Some gaskets have a fractionally smaller diameter which might restrict gas flow.
 
Think I killed the post cat sensor with the vibration from the air hammer got a code for it no signal, just another job to do got to put a replacement expansion tank in first, it's got a crack on the side
 
New post started on the stuck exhaust sensor and the difficulty accessing the remaining two exhaust joint rusty bolts to split the joint so the rear cat could be removed to get clear access to the stuck sensor off the car.
https://z4-forum.com/forum/viewtopic.php?p=2011655#p2011655
Cut to finger has stopped work at the moment and off on hols next week so its on the back burner for now.
 
Hope you're finger heals soon, have a great holiday.

Gutted to hear about the sensor........what a nightmare :thumbsdown:
 
Did mine a while back broke a few drill bits while doing it,luckily I’ve an inspection pit in my garage😉
 

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Finally doing mine. What a job to get to !. Ordered new gaskets from Euro. Wrong size ( huge) so I went in to my local dealer
£25 each !!
 
I got all 4 bolts out eventually thanks to oxy acetylene. All nice and quiet, but the post cat sensors died. One came out ok (ish), but the other took 3 hours, and much blood and swearing.
I can’t get a thread chaser to start in the hole in the manifold. I have ordered a proper tap to try and clear the threads. Removing the exhaust manifolds looks like an absolute nightmare of a job to take on. Anyone got any words of advice please 🤞
 
As I said earlier got mine down at Mr Exhaust. They were familiar with the issue as other BMWs suffer from this issue. If you have a Mr Exhaust near you take the car to themj
 
Success is mine !
I bought a tap from Amazon. I had to grind it down to make it into a tapered tap, and after a few failures, it started, and cleared the threads ok. Really awkward to get to, but it’s done. New Bosch sensors fitted, and no warning lights 😀
 
It’s all too easy to mix up the sensors when refitting. I doubt that it makes any difference to running, but while chasing another fault my code reader informed me I’d mixed them up 😡
 
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