catalytic converter gasket

The bolts (3) holding my catalytic converter gasket tight have rusted through. I can purchase a new gasket but how do I fit it over the end of the catalytic converter or the end of the header pipe? The hole of the gasket is smaller than the connecting ends of converter and header pipe. Am I missing something really obvious?

[Clifford Pope]

Do you mean the metal ring, looking like a very thin doughnut?
It goes in between the bell-shaped openings of the down-pipe and cat pipe, clamped by the two rings which are permanently assembled, but loose, on their respective pipes.

Or I think there is another system with a fixed cat flange?

If there was a thin metal ring between the two pipes its long since gone. I am left with the two permanently assembled rings, one on each end of their respective pipes with bolts/nuts rusted firmly in place. Suggestions? (Remove bolts by whatever means neccesary, replace thin metal ring and bolt back together?) Thanks for the input.

[Clifford Pope]

That's what I did - like you, the metal ring was long gone. Angle grind or hacksaw the bolts, but MIND THE OXYGEN SENSOR wires.
If yours is the same pattern as mine (And I do have this feeling there is an alternative type) then the metal ring is of about 1/4 inch section, with two cone faces that mate into the flared ends of the two pipes. When tightened up it is hardly visible, but vital for gas seal and compensating for any tiny misalignment.

Yep,, sure sounds like were talking about the same animal. Thanks for the advice. It should be loads of fun removing those rusted bolts and nuts. Thanks again.

[Peter D]

Use a drill and drill one or two holes colse together in the side of the nut then when you try to undo it the nut will let go and you can get it apart. Do not hit it with a manner the chock does not do the Cat any good. Obtain some sutable M8 bolt, nuts and washers ideally SS, The bolts in the flange may be the pressed in type without heads on them so if the bolts are OK then gasket, washers and new nuts or press out the bolts. I did one recently but had to remove the cat from the rear box so access to remove the pressed in bolt/studs was easy. Regards Peter

Peter,
Made the repair. Drilled the nuts as you suggested. Seems to be working (cars much quieter). Not a pleasent repair job. Thanks for the advice. Brian

[Clifford Pope]

Glad to hear it's sorted. As I half suspected, yours seems to have been of a different pattern from mine. My bolts are entirely free, not pressed in at all, so cutting through the shank releases the entire bolt.