Tuesday, June 19, 2012

1926 Chevrolet Overheating Test


INSTALLING AN ENGINE HEAD
By Bob and Dave 
In an earlier article I explain how the water in my 1926 Chevrolet radiator wanted to blow itself out, rising and falling over time until it would finally overflow the filler tube. Each time it would raise a little, water would go into the overflow pipe and out of the system, causing a great loss of water within a few miles. We determined it was either a cracked head or a leaking head gasket, but when we pulled the head, we also found a tremendous buildup of rust flakes in the engine block. What should a person do to make certain you have corrected the problem?
Some of our considerations:
We inspected the head and the block very closely and found approximately 2 inches of rust flake in the water jacket of the engine block. This was removed with a combination of magnets, wires, vacuuming and pressure washing with the water pump off. Pressure washing worked the best.
The cylinders were then checked for wear and scoring of the cylinder walls. The cylinders passed inspection. The cylinders had been over bored by 0.030 inches, but this was not a concern.
We had the head magnifluxed to ensure there were no cracks. The head had no cracks.
An inspection of the head revealed valves deeper set in the head than desired. This was the result of repeated valve grinding. The result is less gap for exhaust to escape and air fuel mixture to enter when the valve is open, affecting the performance of the engine. This was a concern even though we did not believe this caused the original problem. The head was resurfaced which brought the valves out of the pocket, exposing more of the valves and increasing the gap for exhaust gases to escape and air fuel mixture to enter.
Then there was a debate over the use of mild steel or stainless steel valves. The use of stainless steel valves prevents the valves from welding to the seats when the engine gets very hot and zinc additives are not used. Dissimilar metals do not weld. So we went with stainless steel valves.
Valve guides were checked by rattling the valve while in the head. The valve guides were very worn, so we had new valves and valve guides installed.
Dave has experienced sticking valves when stainless valves are used if the guides are honed as done normally, so we addressed this concern by honing out the valve guides a little more than normal.
We sanded the surface of the block to remove any bumps that might prevent the gasket from doing its job. A couple of guide bolts were turned into the block to guide the placement of the gasket and the head, and the gasket and head were placed in position. Since the last head had some leakage past the head gasket, we used a copper spray on both sides of the head gasket to reduce this potential.
We used the original head bolts but found this was not good. We tightened the head bolts to 60 foot pounds, and then decided they could be tightened more, so we took them to 75 foot pounds. However, we found we could not get the torque on one head bolt to 75 foot pounds. This surprised us, so we removed that head bolt and laid it next to another head bolt to compare the threads. We found that the head bolt had stretched and was stretching as we tried to torque it to 75 foot pounds. We replaced this head bolt with one that was not stretched. I will now purchase all new head bolts, probably #5 or better, to ensure the head is held as tight as it should be to the block.
The next step was the installation of the rocker arms and push rods. The surfaces of the rocker arms that hit the valves were inspected for wear. If these surfaces are concave, setting the gap with a feeler gauge will result in a larger than desired gap. These surfaces passed inspections.
The rocker arms were adjusted and the manifolds mounted, and we were off running again

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