Cracked Header
Cracked Header
07-04-2002, 12:20 AM
#3
Addict
Rennlist Member
Rennlist Member
Assuming that you have a 951, I beg to differ on welding the headers. They are stainless steel, so whoever does your welding must be very good at stainless. Mine had several cracks, a friend here fabricates stainless fixtures for restaurants and welds constantly. He welded them up, they haven't cracked again thus far, one year and quite a few hard miles later. Then again, you could always buy a new set from B&B ($1k+ I think) or gamble on a used set.
If you do have them welded, I highly recommend that you remove the factory heat shields, since there is also likely to be a crack under there too. Go back with DEI header wrap for insulation. It works better for me than the factory shields.
My headers were cracked-
1-broken off the flange of #4
2-cracked in both the "Y"
3-2/3 cracked at the collector
4-cracked at the flange of #2
If you do your own wrenching and have a welder that you trust, this won't be expensive at all, just time consuming. The other option is to throw money at it. HTH
Dave
If you do have them welded, I highly recommend that you remove the factory heat shields, since there is also likely to be a crack under there too. Go back with DEI header wrap for insulation. It works better for me than the factory shields.
My headers were cracked-
1-broken off the flange of #4
2-cracked in both the "Y"
3-2/3 cracked at the collector
4-cracked at the flange of #2
If you do your own wrenching and have a welder that you trust, this won't be expensive at all, just time consuming. The other option is to throw money at it. HTH
Dave
07-04-2002, 07:01 AM
#5
Race Director
If you weld the headers back together, make sure you have it done by someone who's familiar with thin-wall steel welding. That pretty much rules out all the guys at muffler shops. You need to heat up the part first, then MIG/TIG it (no slag rod-welding allowed) and cool it down slowly afterwards. Then you need to file/grind down the weld to remove all the stress-risers.
But that may not solve the actual CAUSE of the crack to begin with. Which is the differential expansion rates of a steel header on an aluminium block (steel expands less for same temp-increase). One way around that is to slot the bolt-holes on the header. Then attach it to the block with a spring between the bolt and header. Don't tighten it down all the way so that only spring-tension pushes the header against the block for a seal. Then as the block expands, the header-to-block interface is allowed to slide against each other; no stretching of the header allowed!
But that may not solve the actual CAUSE of the crack to begin with. Which is the differential expansion rates of a steel header on an aluminium block (steel expands less for same temp-increase). One way around that is to slot the bolt-holes on the header. Then attach it to the block with a spring between the bolt and header. Don't tighten it down all the way so that only spring-tension pushes the header against the block for a seal. Then as the block expands, the header-to-block interface is allowed to slide against each other; no stretching of the header allowed!
