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Hi Buick Fans,
I have been working away trying to find the cause of the water leak in my 300. Thought I would share my findings with the "experts" on this forum. It complex and interesting, I will try and keep my finding as short as possible, as always please feel free to question my post if you have any suggestions or advice.
In short it looks like I have a crack in the LHS head, this is where the bent pushrods and seized valves were found (cylinder 3). I made a test rig, consisting of a stand to hold the head, brass blanking plates and a test gauge with compressed air inlet. The test was completed with the head submerged in heated water.
First, I made the blanking plates and added 30 psi of pressure, over about 10hrs the pressure leaked out. I submerged the test rig in hot water and re-pressurised finding a small leak on a blanking plate that was easy to seal, for a while it was holding pressure. Next, I noticed the pressure was increasing. I thought this was from heated air expanding in the water jacket and creating pressure.
I started to notice bubbles escaping from the (not sure on terminology here) balance port that allows exhaust gas to travel across the inlet manifold from the RHS head and out the LHS exhaust. the bubbles were steady and consistent regardless of the air pressure applied. I noted the bubble location was above cylinder 3. This is where it gets interesting....
I removed air pressure and left it alone for a few hours, when I came back it was still leaking bubbles at the same rate, this was with the ball valve open on my test rig. I thought how can air be escaping the head and not through the open ball valve? obviously, the angle and position of the head had an influence on the bubble escape path, but it just didn't make sense. I closed the valve on my air inlet point and noticed a pressure increase, by this stage the water had cooled. It all got the better of me so I left it overnight.
Next morning there was no change, bubbles escaping and pressure increasing when the valve was closed. I came to the conclusion it must be gas not air, so I held a flame against the bubbes and yep, they crackled and burnt. I spoke to a mate of mine who is an industrial chemist, he explained it appeared to be hydrogen as the gas bubbles imploded not exploded and hydrogen is generated when a metal reacts with acid. The heads had been submerged in acid during machining and very possible a residual was still in the cast iron.
I let it sit another night and found the next morning there were no bubbles or pressure. I added compressed air and had bubbles and pressure generation instantly. This led me to the thought I have a small porosity crack in the head.
Lucky for me I'm in the process of buying another 300 from one of Chucks mates, I will strip the heads off the engine and fit to mine. If anyone has a set of 300 heads laying around, I'm interested so I could have two running engines.
I will post a few photos to help explain my process, the pink ballon was my hydrogen catcher.
Hope that all made sense, happy to hear from any readers.
Marcus
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