Exhausts and underbody braces - new bolts?

beanie

beanie

Active member
 Bournemouth/Turin
I have an x-pipe and back boxes to fit but I’ve been stalling due to the braces that have to be removed to fit the x-pipe.

I’ve noticed in the bmw instructions that they say to replace the bolts (doesn’t specify to use new ones but may mean you should) then torque, some simply to a value and others to a value and then an angle. I assume the ones with an angle are stretch bolts and should be replaced with new?

What has everyone done regarding this?

If you scroll to the bottom you can see the BMW instructions.
https://www.billswebspace.com/MZ4ExhaustRR.htm
 
The brace bolts should come out in good condition, but the old nuts and bolts on your X-pipe will likely be seized and need cutting assuming they haven't been recently replaced, so good to have new ones on hand.
 
This is a good question beanie. I haven't taken my plates off yet but do intend to over winter so I can check the drive train etc. The plates are obviously structural and I wouldn't want to stretch those bolts twice. I read those instructions as 'renew the bolts' and I'm guessing if the old bolts are re-fitted there may be insufficient 'nip' on the plate and may cause the plate's holes to elongate with chassis flex?
I wonder how much new bolts are?
 
MikeyP said:
This is a good question beanie. I haven't taken my plates off yet but do intend to over winter so I can check the drive train etc. The plates are obviously structural and I wouldn't want to stretch those bolts twice. I read those instructions as 'renew the bolts' and I'm guessing if the old bolts are re-fitted there may be insufficient 'nip' on the plate and may cause the plate's holes to elongate with chassis flex?
I wonder how much new bolts are?
Click to expand...

Yup, don't agree with the other comment. The instructions saying replace mean new bolts IMO not replace them in situ if you read the context of the rest of the instructions.
When I had my underside refresh I replaced them anyway and pretty sure I was told they are technically one use although sure you'll get away with reusing a few times. If they've never been replaced before though not a bad idea to get new ones, can't remember them being that expensive but then it was a while ago....
 
Thanks for the thoughts guys.

The instructions really should be clearer to avoid confusion as ‘Replace’ can be interpreted in both ways. I’m sure I’ve reused bolts on other cars that were technically single use and no subframes ever departed company from the body, but I think I may just buy the angle torque bolts for peace of mind.

I think I have some new bolts for the front reinforcement plate so I’ll check realoem just incase they’re the same. I somehow doubt it though!
 
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