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Exhaust bolts


spacewrench

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spacewrench

I'm organizing the repair of a stripped clutch spline on a 2000 R1100S.  Transmission is sorted, but I'm inclined to fix or improve everything I had to move to get there.  Exhausts got new ceramic coating, fuel lines got QDs, etc.

 

The exhaust manifold bolts are nasty.  The nuts came off OK, but the bolts are corroded.  (The aft bolts were seized or broken and will be replaced by new.)

 

I have two questions:

 

* Apart from anti-seize, is there anything I can do to protect the header-to-cat bolts or make them easier to remove in the future?

 

* Thumbs up or thumbs down on replacing the studs in the head?  They're nasty, but if I don't crank the nuts down, there's a chance they'll survive the current reassembly.  But if they're easily and reliably replaceable, I'd do it to avoid a worse problem later.

 

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8 hours ago, spacewrench said:

I'm organizing the repair of a stripped clutch spline on a 2000 R1100S.  Transmission is sorted, but I'm inclined to fix or improve everything I had to move to get there.  Exhausts got new ceramic coating, fuel lines got QDs, etc.

 

The exhaust manifold bolts are nasty.  The nuts came off OK, but the bolts are corroded.  (The aft bolts were seized or broken and will be replaced by new.)

 

I have two questions:

 

* Apart from anti-seize, is there anything I can do to protect the header-to-cat bolts or make them easier to remove in the future?

 

* Thumbs up or thumbs down on replacing the studs in the head?  They're nasty, but if I don't crank the nuts down, there's a chance they'll survive the current reassembly.  But if they're easily and reliably replaceable, I'd do it to avoid a worse problem later.

 

Morning  spacewrench

 

I have two questions:

 

* Apart from anti-seize, is there anything I can do to protect the header-to-cat bolts or make them easier to remove in the future?-- High temperature anti-seize (like is put on o2 sensors) is usually a good choice. New bolts that aren't corroded also helps future removal.  

 

* Thumbs up or thumbs down on replacing the studs in the head?  They're nasty, but if I don't crank the nuts down, there's a chance they'll survive the current reassembly.  But if they're easily and reliably replaceable, I'd do it to avoid a worse problem later.-- This is a very cautious MAYBE, the studs are easily replaceable IF they come loose without breaking off in the cylinder heads. Some will come out easily & others will fight you to the death.

 

If you have a good feel for how much force that you can apply before breaking a stud then you can try to remove. If in doubt then just leave them until you actually need to replace.  

 

Some studs will come out cold, others take quite a bit of heat on the stud, then allowing it to cool to just above too hot to touch before trying to remove.  

 

If you manage to break one off & there is still a little stud sticking out you can weld on a washer to the stud part that is sticking out, then weld a nut to that washer. The combination of welding heat & the cooling between welding on the washer then welding on the nut will usually allow them to break free. 

 

If you break the stud off at or below the cylinder head alloy then you have big problems as you then need to core drill it (perfectly straight), then drill it out with progressively larger left hand drill bits until you get to thread minor diameter, (if lucky the L/H drill bit will catch & spin the broken piece out), if it doesn't  then you will need to carefully re-thread the hole. The problem with this is that the small  pieces or old stud thread still caught in the cylinder head hole  make breaking off a tap rather easy. 

 

 

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spacewrench

Thanks, DR!  I have to replace the rear header-to-cat bolts because the old ones broke off, but it hadn't occurred to me to replace the nuts on the front -- the exterior still looks OK, but fresh internal threads might help too.

Is there a particular type of bolt that's better for this application?  (Stainless, regular, zinc-coated, black?)   I'd hate to put in expensive stainless bolts if those actually corrode worse, or if they're harder to remove if they do.

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6 hours ago, spacewrench said:

Thanks, DR!  I have to replace the rear header-to-cat bolts because the old ones broke off, but it hadn't occurred to me to replace the nuts on the front -- the exterior still looks OK, but fresh internal threads might help too.

Is there a particular type of bolt that's better for this application?  (Stainless, regular, zinc-coated, black?)   I'd hate to put in expensive stainless bolts if those actually corrode worse, or if they're harder to remove if they do.

 

Afternoon spacewrench

 

Stainless bolts CAN be a good option but you have to know your material & type of thread.

 

As a rule there is less corrosion with most (but not all) stainless steel bolts & nuts (depends on the material)

 

What you usually give up with stainless steel fasteners is some strength, if they are corrosion resistant then  it can't be hardened as easily or as hard as conventional  steel. The other thing is in HOW the threads are made. A lot of online, or hardware store, stainless steel bolts have cut threads, cut threads gall easily, & stainless steel bolts already gall easily so it is a double problem.   

 

Rolled threads are the best but are harder  to find & more expensive when you do. 

 

18-8 Stainless is the least expensive & least corrosion resistant,  316 Stainless is more  corrosion resistant but more expensive, 410 Stainless is special alloy that also has it's place. 

 

For what you are doing probably using stock BMW bolts are not  a bad option as they are fairly high strength, somewhat corrosion resistant & if you break them in the future just replace them again.

 

Zinc coated will help but it will still corrode with time, heat, &  road contaminants. 

 

Just about anything used on a hot exhaust system will eventually corrode or gall.  

 

 

 

 

 

 

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