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53 Chieftain 6 cyl exhaust manifold heat riser valve shaft repairs

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Hi All

my 53 Chieftain manifold is showing signs of age and wear in the heat riser butterfly valve shaft / manifold . Recently its had a spray  weld  repair to fix a longitudinal crack in the directional change area of the hot box  that is a common failure over the years. Weld shop did an excellent job of the repair.
Ive  also refitted the manifold to the block using Belleville spring washers and reduced the torque setting applied to the brass manifold nuts  to allow a little more give to allow for heat cycle expansion on the old cast iron to avoid over stressing it again and try to minimise the crack from re-appearing.

However when its on clold start and warm-up, there  is  an annoying exhaust leak from the butterfly valve shaft on the counterweight side. When its reached  normalized operating  temp and the valve moves to fully open the leak is minimised .  Obviously  a  worn shaft  / manifold as was obvious when i measured radial movement jof the shaft just prior to refitment. I needed to move the vehicle  to dry storage so it had to be functional to drive it. Now its in dry storage im looking to repair the leak permanently but still retain the functionality of the heat riser valve . Ive seen other classics with  the valve removed and the shaft holes plugged off, however the preference is to retain it as standard. 


Hence my question is to others who may have completed a permanent repair to reduce the leakage. Particulary with material spec details of a bush that may have been fabricated and installed in the cast manifold to minimize the radial clearance to the shaft. Bronze ? Steel ? clearance to the shaft to minimise leakage and binding ? 


Any previous experiences / guidance would be greatly appreciated.




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