I had pulled the manifold off to replace the gasket, which had blown out on the forward exhaust port. Ordered new extra thick washers on ebay and when they arrived I put it back together with new bolts. Did the least I could do before firing it up and testing it for leaks. It was leaking in the exact same spot where it had blown out before. Took it back apart and gently cleaned up the exhaust part of the manifold where it contacts the head. I could tell the exhaust ports were all slowly deteriorating, but the intake ports were like new. After chipping off rust flakes with a chipping hammer , and a gentle brush with the grinder I put it back on the tractor. Tightened her down evenly and fired the tractor. No leaks, was totally surprised. I let it get hot, then tightened the bolts again, and finished putting it back together. Went ahead and ground two loads of feed with it, then retightened the bolts a bit more. all seems well though I suspect only for awhile. I noticed that the exhaust manifold metal where it seals to the head is definitely thinner than the intake metal. Sooner or later will have to replace the exhaust manifold. That leads to a couple questions. In order to part the one from the other it does seem best to cut the heads of the four bolts holding them together. At this stage will the two separate easily leaving the four headless studs sticking out of the intake, or will they still need persuasion to come apart? Also what is the heat riser that is mentioned often here. I take it it may be a flapper that cases heat from the exhaust manifold to warm the intake when the engine is cold. Seems when I bought mine in 1985 it did have a bimetal coil on the outside of the manifold , but it soon fell off and the rod that it turned has long been seized. Is that thing worth reactivating? I know the tractor is cold natured when first started, but once it warms up it runs fine.
Thank you all for the help!!, YC