Correct Location and Installation of Exhaust Manifold Spherical Washers and Lock Nuts

[Sam Buchanan]

I perused the P15 Service Manual for torque values and locations for the exhaust/intake manifold nuts and the only thing I found was in the Engine section where it stated 15-20 ft/lbs for manifold stud nuts. There are three types of nuts and washers used in this application, some brass and some locking steel. The illustration below may offer insight to their proper placement.

 

However, if only the outboard studs get the spherical washers and self-locking nuts but all the nuts are torqued to the same value what is the purpose of the special washers and nuts? I assume the concern was expansion changing the length of the exhaust manifold due to heat cycles but how do the special washers accommodate that change? Is 15-20 ft/lbs loose enough to allow the manifold to "slide" under the washer but still tight enough to seal properly?

 

Beats me. Hopefully someone can offer more background details. The image below, which looks like it is from a truck manual, shows the spherical washers and steel lock nuts located on the four outboard studs.

 

Edited February 3, 2023 by Sam Buchanan

[kencombs]

My understanding is that the semi-spherical washers are to positively locate the manifold with regard to the ports.   Without them the manifold can move in two directions a slight amount.

 

edit: Just to clarify, I'm referring to the brass washers used in a few of places, not the funny slotted and tapered steel ones.  Those are a type of low torque but effective lock nuts.

Edited February 3, 2023 by kencombs

[Sniper]

As I understand it, the cone in the nut is forced into the washer so that the nut torques down properly but doesn't apply quite as much clamping force at the block to manifold interface allowing it to float as it heats up and expands.