Exhaust Torque Specifications

• The exhaust manifold is attached to the shiny pipes in the upper right of the picture.Auspuffkr??mmer image by Conny from Fotolia.com
  
  The exhaust manifold gathers the exhaust gases from several cylinders and funnels them into the exhaust pipe that takes them to the catalytic converter, muffler and outside world. The fit between the exhaust manifold and the cylinder head must be correct or the exhaust gases will leak. The fit is controlled by the tightness of the bolts connecting the exhaust manifold to the cylinder head.
  
  

Construction

• The designers of the engine were aware that the cylinder head and the exhaust metal twist and contort because of the heat generated by the engine. They put a gasket of a softer material between the two to absorb the changes and maintain a leak-proof seal. The gasket isn't able to withstand the pressure of the exhaust gases without support along its entire length from both pieces of metal. The bolts holding the cylinder head and exhaust manifold together also stretch and contort. The designers require that the bolts be tightened enough to keep the fit strong but not enough to damage the bolts.
  
  

Preparation

• The mechanic installing the exhaust manifold needs to read the instructions from the manifold manufacturer to see if there are any special areas of guidance and to find the specific torque values for the exhaust manifold. The mechanic cleans any leftover gasket material, dirt or grease off the surfaces of both pieces of metal and inside the bolt holes. He places the gasket against the cylinder head, holding it in place with a dab of locking material.
  
  

Installation

• The mechanic presses the exhaust manifold in place and secures it with all four bolts finger tight. The instructions from the manufacturer give the mechanic a sequence for tightening the bolts, usually beginning with the two inner bolts and then alternating the two outer bolts. The mechanic tightens the bolts with a torque wrench, a special wrench that shows the mechanic the force he's using in foot-pounds. A foot-pound is the amount of force necessary to lift a 1-pound weight 1 foot in the air. The mechanic tightens the bolts in stages; finger tight, an intermediate tightness and then the final torque.