2.5 Exhaust Downpipe joint rusty bolts replaced

colb · Post by **colb** » Wed May 24, 2023 7:56 pm

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.

j3nks79 · Post by **j3nks79** » Thu May 25, 2023 8:40 am

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.

TOMGREEN413 · Post by **TOMGREEN413** » Thu May 25, 2023 11:33 pm

Congratulations Sir.....mine look similar but can't face dealing with it at the moment..

Street · Post by **Street** » Fri May 26, 2023 7:15 am

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!!

colb · Post by **colb** » Fri May 26, 2023 11:00 pm

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.

TOMGREEN413 · Post by **TOMGREEN413** » Sun May 28, 2023 12:23 am

Great idea, I'll remember this hack

Z4Mariner · Post by **Z4Mariner** » Sun May 28, 2023 10:15 pm

I bookmarked this too - it would have come in handy when I owned my 325xi . . . . I think I only went through 4 drill bits.

Mike6 · Post by **Mike6** » Tue May 30, 2023 5:06 pm

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.

colb · Post by **colb** » Tue May 30, 2023 5:20 pm

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

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