I rebuilt this one on a 1949 GMC 228. It was stuck and with new bushings and a stainless steel shaft it worked as it should after being re-assembled. The photos will give you a good idea of what's going on inside the exhaust manifold.
Attachments
Weight, Shaft, Spring and Bushings.jpg (329.45 KB, 282 downloads)
Reassembled - Weight.jpg (220.91 KB, 289 downloads)
Reassembled - Valve.jpg (279.79 KB, 283 downloads)
Reassembled - Spring.jpg (255.03 KB, 280 downloads)
Manifold Heat Riser and Heat Control Valve.JPG (20.51 KB, 273 downloads)

Andy

His: 1947 Chevrolet 3104
Hers: 2008 American Saddlebred

"I proudly Stand for the Flag and Kneel for the Cross" Unknown