stainless steel bolts into cylinder head?

nickb777 · May 2, 2011

Just had to enlarge my m6 intake manifold holes to m8 to attach the s/c manifold, question what’s the best bolts to use, not certain I should use SS into aluminum.

exmantaa · May 2, 2011

I would not use SS bolts. Plain zinc coated should do fine. Could take some 12.9 bolts; stronger but more brittle than 8.8. Try 10.6 if you can find them.

How come the M6 bolts sheared? And which ones exactly?
Heard that now a few times on SC's, but seems so unlikely if fitted correctly with lower mani bracket...

nickb777 · May 2, 2011

Will try to get some zinc one, since I took zinc out thought that would be the case, doesn't help bank holiday and trying to get this sorted asap.

The one which failed ( second time now) were closest to number one cylinder the one directly over the intake and the one at the side next to it. This manifold DOES have the support bracket as well, wonder if it's pressure with the m6 just not being man enough. was only running about 18psi not certain what will happen with 28psi notsure.gif

vocky · May 2, 2011

I have some bolts if you need them, but you would have to collect them

nickb777 · May 2, 2011

I have been asked by my wife to nip over to Mk to buy some furniture,so could turn a loss of a trip into something good, great

if you don't mind pming me your post code

I can also drop that saab engine plate off

vocky · May 2, 2011

done

cavaddict · May 5, 2011

Out of interest, is there any reason not to use stainless bolts?

winstar · May 10, 2011

nickb777 said:
Will try to get some zinc one, since I took zinc out thought that would be the case, doesn't help bank holiday and trying to get this sorted asap.

The one which failed ( second time now) were closest to number one cylinder the one directly over the intake and the one at the side next to it. This manifold DOES have the support bracket as well, wonder if it's pressure with the m6 just not being man enough. was only running about 18psi not certain what will happen with 28psi notsure.gif

The clamp load (ie torque isn't high enough you need to go up in either size or grade (or both) to get more clamp force on the joint up. you may need to do a thread stripping calc or helicoil it to get strength

cavaddict said:
Out of interest, is there any reason not to use stainless bolts?

commonly available stainless bolts are A2 or A4 - 70 which are weaker than a steel 8.8 until you get above 450'C but even then there is not much in it. Stainless is also alot more brittle and will fast fracture. The only place I use normal SS is on exhausts or exposed low load bearing applications. B286 or inconel is another matter but they cost £££