An Exhausting Situation

I was driving around in my latest purchase, a 1967 Olds Delmont 88, assessing the cars needs and trying to get a good idea of just how much I can trust this hulking behemoth on the open road. One thing I noticed was that the engine was running as though there was a major restriction in the exhaust. From my pre-purchase inspection I knew that the muffler and pipes were mostly original and in sad shape. The entire exhaust is in dire need of replacement due to rust, holes and leaking, but not a restriction, or so I thought. To exasperate the situation, the car had a major heat soak problem which was causing a hard start condition after it was warmed up. If you have ever worked on a early GM product you know that most are equipped with a heat controlled valve located at the end of one of the exhaust manifolds. The purpose of this valve is to re-direct the exhaust gasses when the engine is cold, up through the center of the intake manifold, passing them directly under the carburetor and then exiting through the opposite head and finally dumping into the exhaust manifold. Why you ask? Well, GM engineers discovered that this method not only warmed up the engine quicker but also aided in making the motor run smoother when it was cold.

The valve in question is counter weighted and controlled by a bi-metal spring. It's natural state is in the closed position, only opening when the spring heats up from the exhaust heat and starts to coil up, opening the valve in the process. GM engineers installed a counter weight to aid the spring in the opening process and also to act as a fail safe in case the spring broke. What they didn't account for was the valve seizing up, rendering both the spring and weight useless. I checked the valve on the Olds and it wouldn't budge. It was seized solid and I had the sneaking suspicion that it was in the closed position. Unfortunately there is only one way to find out for sure, you have to pull the exhaust crossover pipe down from the manifold. This sounds simple enough but consider that the bolts in the exhaust flanges have probably not been touched in over 40 years! My initial thought was to take the slow approach and muscle the bolts out using a socket and ratchet. As I started to crank on one of the bolts, something just didn't feel right. I got this sick feeling that the bolt was about to twist off and then I would really be up a creek. At this point I figured I had nothing to lose so I abandoned the ratchet and broke out the impact gun. This turned out to be a good decision as it made quick work of removing all the flange bolts - in one piece!

As you can see the bolt on the right was real close to breaking.

As soon as I removed the crossover pipe all of my suspicions were confirmed. The valve was stuck in the closed position. At this point you basically have two choices, you can either get the valve working again or remove it. I chose the latter and decided to remove it permanently, but this is no easy task if you plan on doing it while the manifold is still bolted to the engine.

A little restriction anyone?

As you can see by the photo the selection of tools available for this valves removal is very limited given the space constraints. My initial thought was to use a cut off wheel to remove the plate and just leave the shaft in place. This was easier said then done as there is just no room to maneuver the tool up to the plate. I had to come up with another way to remove this valve that didn't involve removing the exhaust manifold. Finally I came up with a plan. My idea was to use a cold chisel to break the shaft at each end and remove the entire plate. I figured the whole thing was nice and brittle from all the heating and cooling cycles over the years. I think this would have worked if I could have hit the end of the chisel with a hammer, but once again I found out that there was not enough room to swing the hammer because the chisel was just too short. While I was looking for a longer one I ran across a bit that fit my air chisel. Before you could say "Bobs your Uncle" I had come up with a new plan.

Armed with my air chisel I crawled under the car to attack the valve. In less then a minute I had the whole thing out. The shaft sheared cleanly on the inside leaving the counter weight intact on the outer piece of the shaft. It was still seized up and the inner edge was bent a little so I wasn't too worried about it falling out. What a piece of cake! I don't know why I didn't think of this in the first place.

This is what was left of the offending valve.

After the valve was out I cleaned up the flanges of the crossover pipe and buttoned it back up with stainless steel hardware. I also coated all the bolt threads with anti-seize to make future removal easier. Now that the stuck heat riser valve was taken care of, the next step is to address the exhaust, which is in dire need of replacement. I'll cover the exhaust system makeover in another blog because, if you'll pardon the pun, I'm exhausted!