|The MGA With An Attitude
|EXHAUST MANIFOLD Shrinkage And Cracks -- EX-108
It is important to install the exhaust pipe support brackets, items 22 and 23 in the illustration. The top strap is actually longer and more vertical than shown. The two straps attach to the welded "L" bracket on the exhaust pipe, while the other ends go to bolts on the bellhousing. I find the longer strap running upward is often the wrong length, either too short to reach the correct bolt on the bell housing, or ending up with a bow in the middle doing nothing useful. I suppose this is a result of the bracket being welded to the pipe in wrong location.
The shorter horizontal strap is very useful in keeping the pipe in correct relation to the engine when the engine shakes about on the rubber mounts. Without this strap it is common to break the bottom flange of the iron manifold (see following articles). I have experienced short life (frequent breaking) for the short horizontal strap in original configuration. Doubling up on the short strap (using two in place of one) seems to solve that problem. Otherwise make a new one from 1/8-in (3-mm) thick steel strap, good forever.
A crack at the "Y" junction has a rather odd origin. Heat cycling of the manifold causes it to change shape slightly over time. The outer arms eventually get closer together, so the two end manifold bolt holes will not line up properly. You may find it difficult to remove or reinstall the manifold over the two end studs. This misfit will cause stress that can lead to cracking of the manifold at the "Y" junction. If you find this case, use a rat tail file to elongate the end holes in the manifold to achieve a free sliding fit on the end studs for installation. And if you have to do it again five years later, so be it. I believe later production manifolds have an addition thin web cast between the arms to inhibit such cracking. I do not know if this reduces the shrinkage problem.
This long term creep in shape of the manifold will also lead to misalignment of the exhaust ports between head and manifold. If this a concern, you can use the manifold gasket as a template to scribe around the ports in head and manifold, then grind away excess metal to match the ports for best exhaust flow. Photo at right from March 15, 2015.
Photos below from April 14, 2016 and April 30, 2016. I finally got tired of replacing used exhaust manifolds that break in this manner, bit the bullet and bought a new one from Moss Motors.