Best bolts for exhaust/catalytic convertor

[jammy_basturd]

For use on a TVR Cerbera. The exhaust gets pretty darn hot. I've used stainless bolts from Halfords in the past, but every time I think the expansion and heat cycles ruins the threads and they become impossible to undo, always requiring a lengthy spell with a hacksaw blade to take the exhaust off.

So what would the best bolts be to use, that would best deal with the heat cycles? Titanium? Gold? Or just something soft to lessen the amount of time it takes a hacksaw blade to cut through them?

[dmitsi]

What size bolts do you need?

[Spangles]

I always struggle with cat bolts no matter what the car. I think investing in an angle grinder would be the best bet.

[jammy_basturd]

dmitsi said:

What size bolts do you need?

I think they're roughly M12 x 50mm.

Got the angle grinder, haven't got the room around a couple of the bolts to use it!

[Nick1point9]

Gold bolts? are you mad? It's soft as puppy st and has no fatigue performance whatsoever, so you want to make a fastener out of it, induce loads in the kN in it and subject it to vibration?

Just use mild steel. Yes it corrodes but it won't fail and it's cheap. Why are you removing it so often that it's a problem? And with a bit of gentle heat most cat bolts/nuts will undo because they stay hot enough that they don't actually corrode that badly compared to other bolts.

[jimbob82]

+1 for mild steel. Can't you use mild steel studs and get copper nuts? I've never had a problem with copper nuts on steel studs even on turbo cars...

[bgunn]

Stainless is completely useless for this situation as it galls badly, and won't have a great deal of tensile strength either.

Standard 8.8 bolt with brass nuts if you want to be able to get them undone. Or just standard 8.8 bolt with a matching nut and use a grinder/oxy-acetylene to remove.

Edited by bgunn on Tuesday 21st May 15:59

[Krikkit]

+3 for brass nuts/mild studs - come undone every time.

[jammy_basturd]

Thanks guys, will get ordering some mild steel bolts and brass nuts!

[one eyed mick]

just give them a liberal coat of copper grease , idealy Coppaslp or Nevva seize when you put them together ,if it will stand truck turbo heat it will be ok for your blackpool special

[Nick1point9]

Can I raise my earlier point of why are you removing it so often it's a become a problem?

[williredale]

Nick1point9 said:

Can I raise my earlier point of why are you removing it so often it's a become a problem?

Cat back on for MOT and off for the rest of the year?

[Nick1point9]

williredale said:

Nick1point9 said:

Can I raise my earlier point of why are you removing it so often it's a become a problem?

Cat back on for MOT and off for the rest of the year?

D'oh hadn't thought of that.

[The Black Flash]

Krikkit said:

+3 for brass nuts/mild studs - come undone every time.

The 4 which twisted off when I removed an exhaust manifold at the weekend would beg to differ.
To be fair though, they were 36 years old

[one eyed mick]

The best cure is stop pissing about and leave the cat on

[Barbarossa]

Inconel bolts and silver plated K-Nuts.

[ridds]

Plain old 8.8 grade bolts and a simple flanged nut for mine. Plenty of copper slip (over the remaining exposed thread as well) and I never have any issues. :-)