Intake manifold/cylinder head internal vacuum leak
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==Overview== | ==Overview== | ||
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. | ||
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| + | Here is a quick tip for checking for internal vacuum leak with engine still assembled and running--remove PCV valve and breather vent, with engine idling place thumbs over both grommets in valve covers--if you feel pressure build up after a few seconds there is no leak, if you feel vacuum build up after a few seconds you have a leak--most likely the bottom of the intake gaskets--you're welcome!! | ||
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. | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Carburetors]] | [[Category:Carburetors]] | ||
| + | [[Category:Cylinder head]] | ||
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