I’ve this drawback with a small block Chevy 355ci that my brother and I simply assembled. The engine within the automobile runs nice. However a pal was following me on the freeway the opposite day and advised me later that each time I shifted {that a} small puff of oil smoke comes out the exhaust. Plus, after I decelerate, the oil smoke is there. I can’t see it however he advised me that it’s definitely there.
At first we thought it could be unhealthy valve information seals however the heads are new so I’m guessing this shouldn’t be the issue. So now we’re not likely positive the place this oil is coming from. We thought you may need some concepts. Thanks,
D.T.
This appears to be a extra widespread drawback within the final 10 years. This will have one thing to do with the getting old of the small block Chevy or maybe simply the proliferation of this engine. We really bumped into this challenge a few years in the past and we too thought at first that it was valve information seals. Our engine was not new however we had lately put in a brand new set of heads and a distinct consumption manifold.
The issue is the connection between the consumption manifold and the heads. With unequal deck heights, or maybe poor machining, the angle of the consumption manifold will not be the identical because the angle fashioned by the heads when bolted to the block. What occurs is that the hole on the high of the consumption ports is tighter than it’s on the backside of the ports. Which means that the consumption gasket will not be squeezed as tightly on the backside as it’s on the high of the port.
This wider hole on the backside of the port creates a decreased clamp load scenario the place crankcase stress contained in the lifter valley combines with the vacuum within the consumption ports to push oil from the lifter valley previous the consumption gasket and into the consumption ports. This example is aggravated probably the most throughout engine deceleration when consumption manifold vacuum could be very excessive. Frankly, oil is being pulled into the ports anytime the engine is working. However it’s most noticeable in the course of the excessive vacuum conditions.
Previously, we heard that engine builders typically expressed a dislike for a sure consumption gasket when the actual motive for his or her dissatisfaction was not the gasket however extra doubtless the truth that consumption manifold was not seated correctly on the heads.
The issue is the way to decide if that is the place the issue exists. We ran throughout a easy little software bought by Hughes Engines in Washington, Illinois. He presents a small package of a number of lengths of wax string roughly six inches in size. First you take away the consumption manifold and the gaskets after which place one size of string on every of the 4 corners of the cylinder heads. Then rigorously drop the consumption manifold down onto the heads and set up and tighten all of the consumption bolts.
Subsequent, take away the bolts and the consumption and examine the wax string. In case your manifold will not be sq. to the heads, the higher portion of the string will probably be squeezed wider than the underside. This means that the manifold will not be correctly aligned. This typically is the end result when both the heads or the block has been machined to straighten the deck.
If the gasket will not be fairly squeezed as tightly on the backside, you’ll have to take the consumption to a machine store and ask them to angle machine the gasket floor to take away roughly 0.010-inch or so from the highest of the sealing floor of the ports whereas solely eradicating 0.001-inch or so on the backside. This can orient the gasket to be flush with the cylinder heads and this could repair your drawback.
You possibly can attempt a thicker consumption gasket, but when the surfaces of the consumption manifold and the top will not be aligned, a thicker gasket could not resolve the issue. The most effective wager is to have the consumption machined to enhance the floor clamp load on the gasket and this may eradicated oil getting into the consumption port.
