Re: The Duchess Project: 1940 Super 8 Convertible Sedan

Posted by HH56 On 2014/6/8 11:47:40

The advantage of return oil dropping into the crankcase is there is no pressure in the return line so oil will go thru the filter. In a partial flow setup anything else would have pressure on both lines so oil might not move thru. Plumbing the way they want with the restriction will allow approx 90 percent of the oil to feed the lifters directly while the other 10 percent goes to the filter and clean oil returns to the crankcase to be used again. After the early 40's, that was the way all partial bypass filters Packard used worked.

The original method had all the lifter supply going thru the filter first which was fine if the filter was new or clean. As soon as the filter clogged then flow was reduced and lifters started getting starved for oil and making noise. Even with a clean filter, If a lifter started getting a little tired there could also be not quite enough oil to keep one pumped up if it started leaking a bit more than another.

The first attempt to cure the problem was a special filter with a built in bypass valve that let oil flow directly to the lifters if the filter was dirty. That didn't last very long and they went to the different method of plumbing as described in the bulletin. Too much oil was still going thru the filter and not enough to lifters so 3 or 4 months later they added the restriction to reduce the filter flow. That is pretty much the way all Packard filters worked from then on.