Exhaust - Cat to exhaust springs

[sproutdreamer]

I had a new exhaust fitted a while ago and wondered whether it had been bolted up properly and the was cause of the intermittent low speed rattle/squeal. One of the bolts that goes through the spring on the exhaust clamp was quite loose. The Haynes Manual shows the bolt torque as 32ft lbs so at that the spring is well compressed-so what is the purpose of the two springs?

Regarding the rattle, I am about to loosen off the auxillary belt and try and turn the water pump and alternator by hand and see if that reveals any roughness. I would not bother about the rattle and would wait for it to get worse and self diagnose itself but it is my wife's car and she worries about breaking down in the middle of nowhere!

[sproutdreamer]

I have just realised the answer is that the bolts are "step" bolts i.e. have a shoulder that takes the specified bolt torque and sets the springs at a pre-determined length and tension onto the exhaust gasket. Amazing that the Haynes Manual does not make this clear. I just set the bolt so that the spring compression looks about the same as the side with the proper bolt.

The exhaust fitters that did my exhaust must have snapped one of the special bolts  and replaced it with an ordinary bolt.

[sproutdreamer]

Result  - I fitted a new step bolt to replace the plain bolt that the exhaust shop had fitted. The strange rattle on acceleration has now gone. Ther plain bolt must have had too much or too little tension on the manifold clamp!