downpipe bolts: stainless steel or grade 12.9 heat treated bolts?
Hex head bolts will arrive at 17mm head, or 16mm if you get JIS somehow. They'll be a tough fit.
Allen head bolts (socket head cap screw) will give more headroom, but I had to cut the allen head socket down to get my wrench into them. But they are available in 12.9, unlike the other options.
Any kind of black oxide, zinc coated, blue ultra coat alloy steel will corrode after a short time. Just use anti-seize, that's life.
Stainless does not come in the strength of 12.9 alloy steel.
Currently, I have Mazda OEM hardware - I don't think it's even steel - it looks like a Monel or Inconel. You won't get anything comparable except from Mazda at that price.
Dave
Allen head bolts (socket head cap screw) will give more headroom, but I had to cut the allen head socket down to get my wrench into them. But they are available in 12.9, unlike the other options.
Any kind of black oxide, zinc coated, blue ultra coat alloy steel will corrode after a short time. Just use anti-seize, that's life.
Stainless does not come in the strength of 12.9 alloy steel.
Currently, I have Mazda OEM hardware - I don't think it's even steel - it looks like a Monel or Inconel. You won't get anything comparable except from Mazda at that price.
Dave
not sure but i believe some of the hardware is a higher tensile strength stainless while others are a case hardened alloy. the examples can be found on the engine itself to the manifold. the studs are a stainless material where the manifold nuts are a case hardened steel alloy, i assume to help prevent the stainless studs from grabbing the stainless nuts which would eventually sieze(even though the case hardened alloys still do).
stainless does love to grab and roll when removing it, always use anti sieze when installing exhaust bolts.
most all of the studs on these engines are stainless and grab while removing, like on the twins where just about every stud tends to come out, very annoying. the stainless will grab aluminum and steel but seems to not have any issue backing out of cast iron.
Last edited by RotaryEvolution; Mar 17, 2011 at 07:11 PM.
