Intake manifold/cylinder head internal vacuum leak
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Occasionally, you may experience a vacuum leak into the intake ports from the crankcase of the motor, due to the intake manifold/cylinder head interface not being machined parallel. | Occasionally, you may experience a vacuum leak into the intake ports from the crankcase of the motor, due to the intake manifold/cylinder head interface not being machined parallel. | ||
| − | For example, consider looking at the manifold from an end view, from the front or rear of the car. Unless you're using all brand new parts, you have no way of knowing if the heads, block, or manifold have been machined by the previous owner, so the interface at the manifold/head could be out of parallel. In other words, the gasket might be pinched tightly at the top of the port and sealing fine, but might be wide open to the crankcase at the bottom of the port, allowing oily vapors to be drawn into the intake manifold runner on the intake stroke. The manifold may also be warped a little. No amount of propane or carburetor cleaner will find such a leak due to the leak being on the bottom of the port, where the combustable agent cannot reach. The best way is to insure the elimination of such a problem while building the motor | + | For example, consider looking at the manifold from an end view, from the front or rear of the car. Unless you're using all brand new parts, you have no way of knowing if the heads, block, or manifold have been machined by the previous owner, so the interface at the manifold/head could be out of parallel. In other words, the gasket might be pinched tightly at the top of the port and sealing fine, but might be wide open to the crankcase at the bottom of the port, allowing oily vapors to be drawn into the intake manifold runner on the intake stroke. The manifold may also be warped a little. No amount of propane or carburetor cleaner will find such a leak due to the leak being on the bottom of the port, where the combustable agent cannot reach. The best way is to insure the elimination of such a problem while building the motor. |
==Not all cylinder blocks are cut squarely== | ==Not all cylinder blocks are cut squarely== | ||
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