Bad design?


Gary

When the manifold gets hot, it must be free enough to expand and move slightly on the head. That is why they utilize the special washers and care should be taken not to overtighten. What happens is, over years, things rust up and don't move around like they should, it puts the cast iron in a bind, and cracks develop. The same is true of any exhaust manifold, but sixes are particularly prone to cracking, since they are longer, they must expand proportionally to their overall length. The later years slant six exhaust manifolds have extra reinforcing ribs to help prevent cracking.

D/W

_________________

If it ain't broke, fix it!

My 86 is cracked, seems to be where the exhaust pipe bolts up. Used to be a catalytic converter there. The converter was trashed and stopped up. I took off the converter. Most likely the converter went bad, got hot and cracked it is my thinking then.

Sounds right.

The most common place for cracks is between the main "downspout" and one of the "legs" of three ports. I've never dealt with a slant six with a pre-converter mounted as you say, but that sounds like what happened.

D/W

_________________

If it ain't broke, fix it!