47 Roadmaster Exhaust Manifold

[comet1]

I have a 47 Roadmaster with a "seperated" rear 1/3 of the exhaust manifold. I see that they are sold in sections, or thirds. I thought mine was cracked, but it appears to be loose from the middle section. How are these assembled? Is there a sealing ring or gasket that maybe is missing or cracked? I don't have a service manual; that will probably tell me everything; I only have a manual for a 48-49 Buick that doesn't show anything. Thanks, JB

[Guest DaveCorbin]

Dear JBoros:

The big series Buicks started in about 1933 with 3 piece exhaust manifolds as the cast iron of the time couldn't stand the heat over a 30+inch length and cracked in all kinds of places. The 3 piece exhaust manifold as used on the 1936-1952 320 engine improved the situation considerably, but it's still not great. The usual point of failure is in the center manifold section, where it splits parallel to the length of the engine. This is caused by swelling of the end pieces as they heat and cool. What I have done quite successfully is to buy a new NODULAR iron center section, (Skip Boyer or CARS) very carefully eliminate the sharp machined corners with a small radius both inside and outside of the holes where the front and rear sections fit in. (The sharp corners are where cracking starts.) I then carefully grind down the slide-in part of the front and rear sections so that it slides in as a snug hand fit. (Care and Patience REQUIRED on this!!) Be sure to check the operation of the heat riser flap valve. As I'm ready to assemble it to the engine, the center section is already bolted to the intake manifold, the end pieces have been coated with high temperature sealer and inserted into the center sections, adjusted by hand to an approximate fit and the new intake and exhaust gaskets put on the little rings inserted into the head and everything already cleaned of old gasket material. Put the assembly on, adjust everything to a snug FINGER tight position and tighten from the center out, alternating from the front of the engine to the back of the engine and tighten in several steps of about 1/4 of a turn of the nuts or 10 ft-lb of torque increments per step, just like putting on a straight 8 cylinder head. This will get you a lasting fix on the exhaust manifold problems. I hope this description doesn't scare you, but this addresses ALL the problems with the original design and the original cast iron materials.

Regards, Dave Corbin